This study was supported by NIH R00HL102154, and an American Society of Hematology scholar award to P Ji.

The experiments described in this protocol were performed in accordance with the guidelines and regulations set forth by Northwestern University Institutional Animal Care and Use Committee.
1. Preparation of Culture Medium
<ol>
	<li>Prepare fibronectin solution. Add 1 ml of water to one vial of human fibronectin (1 mg). Leave solution in the tissue culture hood for 30 min without agitation. Transfer the total liquid to 50 ml of PBS to make a final concentration of 20 &#181;g/ml and gently mix well. Make the fibronectin solution fresh before coating the plate (see below).</li>
	<li>Prepare 50 ml of Epo free medium (SCF medium). Combine the listed ingredients in Table 1. The medium can be stored at 4 &#176;C for 1 month when made fresh.</li>
	<li>Prepare 50 ml of Epo containing medium. Combine the listed ingredients in Table 2. The medium can be stored at 4 &#176;C for 1 month when made fresh.</li>
</ol>
2. Fibronectin Coated Plate
<ol>
	<li>Add 1 ml fibronectin solution to each well of a 6-well plate (or 0.5 ml to each well of a 12 well plate). Leave the plate in the tissue culture hood for 1 hr.</li>
	<li>Rinse wells with sterile water twice and air dry the plate.</li>
	<li>Wrap the plate and save in the cold room at 4 &#176;C.</li>
</ol>
3. Purification of Fetal Liver Erythroblasts
NOTE: Use fetal livers&#160;from E13 to E15 timed pregnant mice (C57BL/6). E13.5 livers are preferred to maximize the yield of CFU-E progenitors. To obtain the timed pregnant mice, 6 to 8 weeks old male and female mice were placed in one cage (usually one male with one or two females). Female vaginal plugs were checked the next morning to determine if the mating was successful. The first day of gestation was the day after the plug was found.
<ol>
	<li>Preparation of the Total Fetal Liver Cells
	<ol>
		<li>Sacrifice the mouse by CO2 inhalation and cervical dislocation. Spray the abdomen with 70% ethanol for disinfection. Open the abdomen with dissecting scissors to remove the uterus. Wash the uterus in 1x PBS.</li>
		<li>Dissect the fetuses under sterile conditions using a tissue culture hood and autoclaved tools and wash in 1x PBS.</li>
		<li>Dissect the fetal livers from the fetuses. Hold the body of the fetus with one forceps, gently pull the fetal liver (pink in color) away from the body with another forceps. Clean the fetal liver with the forceps to remove the associated fibrotic tissues. Place all fetal livers into fresh 1x PBS containing 10% fetal bovine serum.</li>
		<li>Mechanically disrupt fetal livers by pipetting up and down.</li>
		<li>Filter the cell suspension through a 40 &#181;m cell strainer into a 50 ml conical tube. Pellet the cells at 800 x g for 5 min.</li>
		<li>Aspirate the supernatant and resuspend the cells in 1 ml PBS with 10% FBS (approximately 8 E13.5 fetal livers per ml).</li>
	</ol>
	</li>
	<li>Purification of TER119 Negative Erythroblasts
	<ol>
		<li>Block the cells with rat IgG (0.2 mg/ml) on ice for 15 min.</li>
		<li>Without washing or centrifuging, add biotinylated anti-TER119 antibody to the cell suspension (1 &#181;g/ml). Incubate for 15 min on ice.</li>
		<li>Wash in 1x PBS with 10% FBS (1:10) and centrifuge at 800 x g for 5 min. Resuspend the cells in 1 ml of PBS with 10% FBS.</li>
		<li>Add 75 &#181;l streptavidin conjugated with magnetic particles and incubate for 10 mins on ice.</li>
		<li>Add the volume to 2.5 ml with PBS containing 10% FBS. Transfer the cell suspension into a 5 ml polypropylene round bottom tube.</li>
		<li>Insert the tube into a magnetic cell-sorting apparatus and incubate for 10 min. TER119 positive cells will attach to the side of the tube. The unattached TER119 negative erythroblasts will remain in the suspension.</li>
		<li>Pour the cell suspension into a new 5 ml polypropylene round bottom tube.</li>
		<li>Repeat steps 3.2.6 and 3.2.7 to remove the residual TER119 positive cells.</li>
		<li>Pellet the cells at 800 x g for 5 min. Aspirate off the supernatant. Resuspend the cells in 1 ml PBS containing 10% FBS and count live cells with Trypan Blue.</li>
	</ol>
	</li>
</ol>
4. Transduction with Viruses Encoding cDNA or shRNA
<ol>
	<li>Plate the purified TER119 negative fetal liver cells at 3-5 x 105/well in a fibronectin coated 12-well plate (adjust the cell number if using a different plate).</li>
	<li>Add polybrene to a final concentration of 10 &#181;g/ml to facilitate viral transduction. Spin infect the cells with lentiviruses or retroviruses, encoding cDNA or shRNA, at 800 x g for 1-1.5 hr&#160;at 37 &#176;C.</li>
</ol>
5. Culture of the Transduced TER119 Negative Mouse Fetal Liver Erythroblasts
<ol>
	<li>To test gene functions in the early stage of terminal erythropoiesis (Figure 1 dashed lines). <ol. li=""></ol.>
	<ol>
		<li><ol. li="">Culture the transduced cells in Epo free medium (SCF medium) for 12 hr to allow the expression of the transduced genes and maintenance of the progenitor state.</ol.></li>
		<li>Centrifuge the cells at 800 x g for 5 min. Aspirate the supernatant. Resuspend the cells in 1 ml Epo containing medium in each well of a 12-well plate.</li>
		<li>After culture for 24 or 48 hr, harvest the cells for further assays.</li>
	</ol>
	</li>
	<li>Test gene functions in the late stage of terminal erythropoiesis (Figure 1 solid lines).
	<ol>
		<li>Culture the transduced cells immediately in Epo containing medium.</li>
		<li>After culture for 24 or 48 hr, harvest the cells for the further assays.</li>
	</ol>
	</li>
</ol>
6. Staining of the Cultured Fetal Liver Cells for Flow Cytometric Analysis
<ol>
	<li>Wash and resuspend the cells in 1x PBS. Harvest 2 x 105 cultured cells for flow cytometric analysis.</li>
	<li>Incubate the cells with fluorophore-conjugated antibodies for 20 min at room temperature in the dark. To test differentiation, use APC conjugated anti-CD71 and PE conjugated anti-TER119. To test enucleation, use Hoechst 33342 stain in addition to the other antibodies.</li>
	<li>Wash cells with 1x PBS. Resuspend the cells in 0.5 ml PBS containing 1% FBS and propidium iodide (PI) (1 &#181;g/ml) to stain the dead cells and exclude them from analysis.</li>
	<li>Conduct flow cytrometric analysis. Analyze single color stained and unstained control cells first for adjustment and compensation of the flow cytometer.</li>
</ol>

<ol>
	<li>Hattangadi, S. M., Wong, P., Zhang, L., Flygare, J., Lodish, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+stem+cell+to+red+cell:+regulation+of+erythropoiesis+at+multiple+levels+by+multiple+proteins,+RNAs,+and+chromatin+modifications.">From stem cell to red cell: regulation of erythropoiesis at multiple levels by multiple proteins, RNAs, and chromatin modifications.</a> Blood. 118 (24), 6258-6268 (2011).</li><li>Richmond, T. D., Chohan, M., Barber, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Turning+cells+red:+signal+transduction+mediated+by+erythropoietin.">Turning cells red: signal transduction mediated by erythropoietin.</a> Trends in cell biology. 15 (3), 146-155 (2005).</li><li>Eshghi, S., Vogelezang, M. G., Hynes, R. O., Griffith, L. G., Lodish, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alpha4beta1+integrin+and+erythropoietin+mediate+temporally+distinct+steps+in+erythropoiesis:+integrins+in+red+cell+development.">Alpha4beta1 integrin and erythropoietin mediate temporally distinct steps in erythropoiesis: integrins in red cell development.</a> The Journal of cell biology. 177 (5), 871-880 (2007).</li><li>Koury, M. J., Bondurant, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maintenance+by+erythropoietin+of+viability+and+maturation+of+murine+erythroid+precursor+cells.">Maintenance by erythropoietin of viability and maturation of murine erythroid precursor cells.</a> Journal of cellular physiology. 137 (1), 65-74 (1988).</li><li>Ji, P., Yeh, V., Ramirez, T., Murata-Hori, M., Lodish, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Histone+deacetylase+2+is+required+for+chromatin+condensation+and+subsequent+enucleation+of+cultured+mouse+fetal+erythroblasts.">Histone deacetylase 2 is required for chromatin condensation and subsequent enucleation of cultured mouse fetal erythroblasts.</a> Haematologica. 95 (12), 2013-2021 (2010).</li><li>Dumitriu, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sox6+cell-autonomously+stimulates+erythroid+cell+survival,+proliferation,+and+terminal+maturation+and+is+thereby+an+important+enhancer+of+definitive+erythropoiesis+during+mouse+development.">Sox6 cell-autonomously stimulates erythroid cell survival, proliferation, and terminal maturation and is thereby an important enhancer of definitive erythropoiesis during mouse development.</a> Blood. 108 (4), 1198-1207 (2006).</li><li>Rector, K., Liu, Y., Van Zant, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comprehensive+hematopoietic+stem+cell+isolation+methods.">Comprehensive hematopoietic stem cell isolation methods.</a> Methods in molecular biology. 976, 1-15 (2013).</li><li>Rossi, L., Challen, G. A., Sirin, O., Lin, K. K., Goodell, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hematopoietic+stem+cell+characterization+and+isolation.">Hematopoietic stem cell characterization and isolation.</a> Methods in molecular biology. 750, 47-59 (2011).</li><li>Choi, H. S., Lee, E. M., Kim, H. O., Park, M. I., Baek, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Autonomous+control+of+terminal+erythropoiesis+via+physical+interactions+among+erythroid+cells.">Autonomous control of terminal erythropoiesis via physical interactions among erythroid cells.</a> Stem cell research. 10 (3), 442-453 (2013).</li><li>Bhatia, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Short-chain+fatty+acid-mediated+effects+on+erythropoiesis+in+primary+definitive+erythroid+cells.">Short-chain fatty acid-mediated effects on erythropoiesis in primary definitive erythroid cells.</a> Blood. 113 (25), 6440-6448 (2009).</li><li>Zhang, J., Socolovsky, M., Gross, A. W., Lodish, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+Ras+signaling+in+erythroid+differentiation+of+mouse+fetal+liver+cells:+functional+analysis+by+a+flow+cytometry-based+novel+culture+system.">Role of Ras signaling in erythroid differentiation of mouse fetal liver cells: functional analysis by a flow cytometry-based novel culture system.</a> Blood. 102 (12), 3938-3946 (2003).</li><li>Socolovsky, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ineffective+erythropoiesis+in+Stat5a(-/-)5b(-/-)+mice+due+to+decreased+survival+of+early+erythroblasts.">Ineffective erythropoiesis in Stat5a(-/-)5b(-/-) mice due to decreased survival of early erythroblasts.</a> Blood. 98 (12), 3261-3273 (2001).</li><li>Ji, P., Jayapal, S. R., Lodish, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enucleation+of+cultured+mouse+fetal+erythroblasts+requires+Rac+GTPases+and+mDia2.">Enucleation of cultured mouse fetal erythroblasts requires Rac GTPases and mDia2.</a> Nature cell biology. 10 (3), 314-321 (2008).</li><li>Chida, D., Miura, O., Yoshimura, A., Miyajima, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+cytokine+signaling+molecules+in+erythroid+differentiation+of+mouse+fetal+liver+hematopoietic+cells:+functional+analysis+of+signaling+molecules+by+retrovirus-mediated+expression.">Role of cytokine signaling molecules in erythroid differentiation of mouse fetal liver hematopoietic cells: functional analysis of signaling molecules by retrovirus-mediated expression.</a> Blood. 93 (5), 1567-1578 (1999).</li><li>Patel, V. P., Lodish, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+fibronectin+matrix+is+required+for+differentiation+of+murine+erythroleukemia+cells+into+reticulocytes.">A fibronectin matrix is required for differentiation of murine erythroleukemia cells into reticulocytes.</a> The Journal of cell biology. 105 (6 Pt 2), 3105-3118 (1987).</li><li>Udupa, K. B., Lipschitz, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endotoxin-induced+suppression+of+erythropoiesis:+the+role+of+erythropoietin+and+a+heme+synthesis+stimulating+factor.">Endotoxin-induced suppression of erythropoiesis: the role of erythropoietin and a heme synthesis stimulating factor.</a> Blood. 59 (6), 1267-1271 (1982).</li><li>Koury, M. J., Sawyer, S. T., Brandt, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+insights+into+erythropoiesis.">New insights into erythropoiesis.</a> Current opinion in hematology. 9 (2), 93-100 (2002).</li></ol>

The authors declare that they have no competing financial interests.

Here we present a unique system to chronologically analyze mouse fetal liver terminal erythropoiesis. Through the application of different culture conditions, we successfully dissected terminal erythropoiesis in early and late stages. This is particularly important to determine the mechanisms of genes with multiple functions. For example, Rac GTPases play important roles in different stages of terminal erythropoiesis. Inhibition of Rac GTPases in the early stage of terminal erythropoiesis influences cell differentiation and proliferation. On the other hand, inhibition the activity of Rac GTPases in the late stage of terminal erythropoiesis blocks enucleation without affecting cell differentiation, proliferation, or survival13.
Several important steps in this protocol should be kept in mind. First, E13.5 mouse fetal livers are preferred for the purification of TER119 negative cells. Older embryos can be used but the proportion of the progenitors out of the total fetal liver cells will be low. Second, it is important to use low endotoxin BSA in Epo medium since it is critical for enucleation, although the mechanism is not clear. Third, although fibronectin was reported to be important for erythropoiesis15, we found that the use of fibronectin coated plate was optional. It does not affect cell proliferation, differentiation, or enucleation in our system. However, fibronectin can be useful for the cells to attach to the plate that might be important for certain applications such as immunostaining. Fourth, a small percentage of reticulocytes or late stage erythroblasts may lose GFP signal that was carried with the transduced cells. Alternatively we use human CD4 as a marker to track the transduced cells. Finally, previous reports recommended removal of erythropoietin from the culture on day 111. We found that it was not necessary to do so since there was no significant difference on cell differentiation, proliferation, or enucleation with or without removal of erythropoietin. On the contrary, change of medium may cause cell loss.
Using the same strategy, we recently discovered more than 30 genes that play novel functions in different stages of terminal erythropoiesis (Zhao et al., unpublished results). Like Rac GTPases, many of these genes play dual functions in both early and late stages of terminal erythropoiesis. This indicates that signaling pathways in terminal erythropoiesis are closely interconnected. Genes involved in actin cytoskeleton remodeling and nuclear condensation are those that tend to play dual functions due to the critical roles of these signaling pathways throughout terminal erythropoiesis. On the other hand, genes involved in pathways such as heme synthesis and generation of erythroid specific plasma membrane tend to be more restricted in the early stage of terminal erythropoiesis16,17. Although there are certain limitations of this experimental strategy, such as relatively low infection efficiency compared to transduction of cell lines, and difficulty of knocking down proteins with long half-life, we recommend a routine practice to use our system given the importance of dissecting gene functions in different stages of terminal erythropoiesis. In addition, this experimental strategy can also be used for other applications. For example, using the SCF medium culture condition, genes that are involved in the maintenance of stem cell properties such as self-renewal or differentiation could be analyzed. Using the method for analyzing late stage erythropoiesis, one could also determine the function of genes that could be involved in autophagy for the removal of organelles.
Broadly, this experimental strategy can be applied to the functional investigation of other hematopoietic systems such as megakaryopoiesis and myelopoiesis. Successful application of this strategy would also reveal the hidden side of the molecular mechanisms of specific genes in different developmental stages of blood cells.

Erythropoiesis is the process of differentiation of multipotent hematopoietic stem cells to mature erythrocytes. This stepwise process includes the formation of committed erythroid burst forming units (BFU-Es), the rapidly dividing erythroid colony forming units (CFU-Es), and morphologically recognizable erythroblasts1,2. Terminal erythropoiesis from CFU-E progenitor cells involves sequential erythropoietin-dependent and independent stages2,3. In the early stage of terminal erythropoiesis, Erythropoietin (Epo) binds to its receptor on the cell surface and induces a series of downstream signaling pathways that prevent cell apoptosis and promote rapid cell divisions and gene expression1,4. In the late stage of terminal erythropoiesis, erythroblasts undergo terminal cell cycle exit, chromatin and nucleus condensation, and extrusion of the highly condensed nuclei5.
Our understanding of terminal erythropoiesis has greatly improved in the last few decades, which is largely due to the successful use of several in vitro and in vivo mouse models6-9. Among these models, in vitro culture of mouse fetal liver erythroblasts provides many advantages including the ease of cell purification, fast proliferation and differentiation, and a closer mimic to human erythropoiesis10,11. In this system, large numbers of erythroid progenitor cells from mouse fetal livers can be easily isolated by the single step purification of TER119 (a marker for the mature erythroid cells) negative erythroblasts. During the two-day culture of the erythroblasts, the differentiation of these cells can be monitored by a flow cytometric analysis based on surface expression of the transferrin receptor (CD71) and the TER119 antigen12. In addition, enucleation of the terminally differentiation erythroblasts can be detected by a DNA maker (Hoechst 33342)13. Furthermore, the purified progenitors can be genetically modified by exogenous expression of cDNAs or small hairpin RNAs (shRNAs) for the genes of interest, which facilitates the mechanistic studies of the functions of gene expression on erythropoiesis11,13,14.
On the other hand, the fast cell growth rate can be a double-edged sword since it is difficult to characterize gene functions in different stages of terminal erythropoiesis. In most cases, it is difficult to determine whether a specific gene functions in the early stage of terminal erythropoiesis since by the time the cDNAs or shRNAs expressed, the cells already passed the early stage. To solve this problem, we developed a unique system to dissect the early and late stages of terminal erythropoiesis. For the early stage of terminal erythropoiesis, genetically modified TER119 negative erythroblasts were cultured in Epo-free medium but containing stem cell factor (SCF), IL-6 and FLT3 ligand to maintain their progenitor status and allow the transduced cDNAs or shRNA to expression13. The cells were changed to Epo containing medium after 12 hr to induce cell proliferation and differentiation. In this way, when the cells started to differentiate, the transduced cDNAs or shRNAs were already expressed. For the late stage of terminal erythropoiesis, TER119 negative erythroblasts were cultured in Epo containing medium immediately after transduction. Therefore, one can analyze the functions of the genes of interest in the late stage of terminal erythropoiesis. In summary, a broad application of this system would help dissect gene functions in different stages of terminal erythropoiesis.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Iscove&#39;s Modified Dulbecco&#39;s MediumIMDM (IMDM)</td>
			<td>Gibco</td>
			<td>12440-053</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum (FBS)</td>
			<td>GEMINI Bio-product</td>
			<td>700-102P</td>
			<td></td>
		</tr>
		<tr>
			<td>b-mecaptoethanol</td>
			<td>Sigma</td>
			<td>M6250</td>
			<td>0.1 M in IMDM,&#160; 4&#8451;stock</td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin solution</td>
			<td>Hyclone</td>
			<td>SV30010</td>
			<td>100 X</td>
		</tr>
		<tr>
			<td>L-Glutamine</td>
			<td>Hyclone</td>
			<td>SH30034.01</td>
			<td>200 mM</td>
		</tr>
		<tr>
			<td>Stem cell factor (SCF)</td>
			<td>STEMCELL TECH</td>
			<td>2630</td>
			<td>100 ng/ul, -20&#8451; stock</td>
		</tr>
		<tr>
			<td>Mouse FIT3 Ligand (Flt-3L)</td>
			<td>BD Biosciences&#160;</td>
			<td>14-8001-80</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse Recombinant Interleukin-6 (IL-6)&#160;</td>
			<td>GEMINI Bio-product</td>
			<td>300-327P</td>
			<td></td>
		</tr>
		<tr>
			<td>fibronectin</td>
			<td>BD Biosciences&#160;</td>
			<td>354008</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin (BSA)</td>
			<td>STEMCELL TECH</td>
			<td>9300</td>
			<td>10% stock in IMDM</td>
		</tr>
		<tr>
			<td>Insulin solution, human</td>
			<td>Sigma</td>
			<td>I9278</td>
			<td>4&#8451; stock</td>
		</tr>
		<tr>
			<td>holo-transferrin human</td>
			<td>Sigma</td>
			<td>T0665</td>
			<td>50 mg/ml in Water -20&#8451; stock</td>
		</tr>
		<tr>
			<td>Erythropoietin(Epo)</td>
			<td>PROCRIT</td>
			<td>NOC 59676-303-00</td>
			<td>3,000 U/ml stock</td>
		</tr>
		<tr>
			<td>Streptavidin particles Plus</td>
			<td>BD Pharmingen</td>
			<td>557812</td>
			<td></td>
		</tr>
		<tr>
			<td>EasySep Magnet</td>
			<td>STEMCELL TECH</td>
			<td>18000</td>
			<td></td>
		</tr>
		<tr>
			<td>Polypropylene Round-Bottom Tube, 5 ml</td>
			<td>FALCON</td>
			<td>352063</td>
			<td></td>
		</tr>
	</tbody>
</table>

mouse fetal liver culture system to dissect target gene functions at the early and late stages of terminal erythropoiesis

Erythropoiesis involves a dynamic process that begins with committed erythroid burst forming units (BFU-Es) followed by rapidly dividing erythroid colony forming units (CFU-Es). After CFU-Es, cells are morphologically recognizable and generally termed terminal erythroblasts. One of the challenges for the study of terminal erythropoiesis is the lack of experimental approaches to dissect gene functions in a chronological manner. In this protocol, we describe a unique strategy to determine gene functions in the early and late stages of terminal erythropoiesis. In this system, mouse fetal liver TER119 (mature erythroid cell marker) negative erythroblasts were purified and transduced with exogenous expression of cDNAs or small hairpin RNAs (shRNAs) for the genes of interest. The cells were subsequently cultured in medium containing growth factors other than erythropoietin (Epo) to maintain their progenitor stage for 12 hr while allowing the exogenous cDNAs or shRNAs to express. The cells were changed to Epo medium after 12 hr to induce cell differentiation and proliferation while the exogenous genetic materials were already expressed. This protocol facilitates analysis of gene functions in the early stage of terminal erythropoiesis. To study late stage terminal erythropoiesis, cells were immediately cultured in Epo medium after transduction. In this way, the cells were already differentiated to the late stage of terminal erythropoiesis when the transduced genetic materials were expressed. We recommend a general application of this strategy that would help understand detailed gene functions in different stages of terminal erythropoiesis.

Figure 1 outlines the experimental strategies. The protocol consists of two independent conditions for targeting the functions of the signaling molecules in the early and late stages of terminal erythropoiesis. TER119 negative fetal liver erythroblasts were purified from E13.5 mouse fetus. Flow cytometric analysis of fetal liver erythroid cells before and after purification demonstrated that the purification was efficient (Figures 2A and 2B). For the early stage of terminal erythropoiesis (Figure 1, dashed lines), after viral transduction, the cells were cultured in Epo-free medium (SCF medium) for 12 hr. During this period, the cells showed minimal differentiation (Figure 2C) with no significant apoptosis observed in the transduced cells (GFP positive) (Figure 3). The cells started to differentiate after transferring to Epo-containing medium (Figure 4), which was similar to the cells cultured in Epo containing medium immediately after transduction (Figure 1, solid lines and Figure 5). During the 2 day culture in Epo containing medium in both methods, most of the erythroid progenitor cells (CD71low TER119low) exhibited induction of the transferrin receptor (CD71) and TER119 on day 2 (CD71high TER119high) (Figure 4A and Figure 5A). Enucleation occurred on day 2, as observed by HoechsthighTER119high (erythroblasts) and HoechstlowTER119high (reticulocytes) (Figure 4B and Figure 5B). It is notable that cells immediately culture in Epo (solid line) was relatively more efficient for differentiation and enucleation than cells cultured first in SCF medium (dashed line).
<img alt="Figure 1" fo:content-width="5in" width="500" src="/files/ftp_upload/51894/51894fig1highres.jpg" /> 
Figure 1. Schematic overview of the experimental strategy. Dashed and solid lines represent methods for studying signaling molecules in the early and late stages of terminal erythropoiesis, respectively.
<img alt="Figure 2" fo:content-width="5in" width="500" src="/files/ftp_upload/51894/51894fig2highres.jpg" /> 
Figure 2. Flow cytometric analysis of mouse fetal liver erythroid cells before and after purification of TER119 negative erythroblasts. (A) Total fetal liver cells stained with TER119 and CD71. (B) Purified TER119 negative cells stained with TER119 and CD71. (C) Purified TER119 negative cells after 12 hr culture in SCF medium. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51894/51894fig2highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" fo:content-width="5in" width="500" src="/files/ftp_upload/51894/51894fig3highres.jpg" /> 
Figure 3. Flow cytometric analysis of apoptosis after culture in Epo-free medium (SCF medium) for 12 hr. (A-B) The TER119 negative erythroblasts were transduced with control lentiviruses (A) or lentiviruses encoding green fluorescent protein (GFP) (B). The percentage of the GFP positive transduced cells was presented after 12 hr of culture in SCF medium. (C-D) Analysis of apoptosis in GFP negative (C) and positive (D) cells from (B).
<img alt="Figure 4" fo:content-width="5in" width="500" src="/files/ftp_upload/51894/51894fig4highres.jpg" /> 
Figure 4. Flow cytometric analysis of differentiation and enucleation of the transduced erythroblasts cultured in SCF medium followed by Epo medium. (A) As in Figure 3, GFP negative and positive cells were gated for differentiation analysis using CD71 and TER119 after the cells were changed to Epo medium and cultured for an additional 48 hr. (B) Enucleation assay using Hoechst and TER119 of the indicated cells after 48 hr in Epo medium.
<img alt="Figure 5" fo:content-width="5in" width="500" src="/files/ftp_upload/51894/51894fig5highres.jpg" /> 
Figure 5. Flow cytometric analysis of differentiation and enucleation of the transduced erythroblasts directly cultured in Epo medium. (A) The TER119 negative cells were transduced with lentiviruses encoding GFP. The cells were immediately cultured in Epo medium after transduction. Cell differentiation analysis of GFP negative and positive cells was performed using CD71 and TER119 after 48 hr in culture. (B) Enucleation assay of the indicated cells using Hoechst and TER119 after 48 hr in culture.
<table border="0" cellpadding="0" cellspacing="0" >
	<tbody>
		<tr >
			<td>Ingredient</td>
			<td >Quantity</td>
		</tr>
		<tr >
			<td>IMDM</td>
			<td>41.385 ml</td>
		</tr>
		<tr >
			<td>Fetal bovine serum (FBS, 15%) </td>
			<td>7.5 ml</td>
		</tr>
		<tr >
			<td>b-mercaptoethanol (10-4 M)</td>
			<td>50 &#181;l (10-1 M stock in IMDM)</td>
		</tr>
		<tr >
			<td>Penicillin-Streptomycin (1%)</td>
			<td>500 &#181;l</td>
		</tr>
		<tr >
			<td>Glutamine (2 mM)</td>
			<td>500 &#181;l</td>
		</tr>
		<tr >
			<td>Stem Cell Factor (50 ng/ml)</td>
			<td>25 &#181;l from 100 ng/ml stock</td>
		</tr>
		<tr >
			<td>FLT3 Ligand (FLT-3L) (30 ng/ml)</td>
			<td>30 &#181;l from 50 ng/ml stock</td>
		</tr>
		<tr >
			<td>IL-6 (20 ng/ml)</td>
			<td>10 &#181;l from 100 ng/ml stock</td>
		</tr>
	</tbody>
</table>
Table 1. Ingredient for SCF medium (Epo free medium).
<table border="0" cellpadding="0" cellspacing="0" >
	<tbody>
		<tr >
			<td>Ingredient</td>
			<td >Quantity</td>
		</tr>
		<tr >
			<td>IMDM</td>
			<td>36.3 ml</td>
		</tr>
		<tr >
			<td>FBS (15%)</td>
			<td>7.5 ml</td>
		</tr>
		<tr >
			<td>Bovine Serum Albumin (BSA, 10%)</td>
			<td>5 ml (10% stock in IMDM)</td>
		</tr>
		<tr >
			<td>Insulin (10 mg/ml)</td>
			<td>50 &#181;l from 4 &#176;C stock</td>
		</tr>
		<tr >
			<td>Holo-transferrin (200 mg/ml)</td>
			<td>200 &#181;l (50 mg/ml in Water, -20 &#176;C stock)</td>
		</tr>
		<tr >
			<td>b-mercaptoethanol (10-4 M)</td>
			<td> 50 &#181;l (10-1 M stock in IMDM)</td>
		</tr>
		<tr >
			<td>Penicillin-Streptomycin (1%)</td>
			<td>500 &#181;l </td>
		</tr>
		<tr >
			<td>2 mM Glutamine</td>
			<td>500 &#181;l </td>
		</tr>
		<tr >
			<td>Epo (2 U/ml)</td>
			<td>33 &#181;l (3,000 U/ml stock)</td>
		</tr>
	</tbody>
</table>
Table 2. Ingredient for Epo containing medium.

Watch this Scientific Journal Video about Mouse Fetal Liver Culture System to Dissect Target Gene Functions at the Early and Late Stages of Terminal Erythropoiesis at JoVE.com

Mouse Fetal Liver Culture System to Dissect Target Gene Functions at the Early and Late Stages of Terminal Erythropoiesis

We present an in vitro mouse fetal liver erythroblast culture system that dissects the early and late stages of terminal erythropoiesis. This system facilitates functional analysis of specific genes in different developmental stages.

Erythropoiesis involves a dynamic process that begins with committed erythroid burst forming units (BFU-Es) followed by rapidly dividing erythroid colony ...

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Nanyang Technological University

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Cell Biology

Immunology and Infection

Unit 1

A Hierarchical Stem-Cell System: Blood Cell Formation

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14.9K Views.  Northwestern University. We present an in vitro mouse fetal liver erythroblast culture system that dissects the early and late stages of terminal erythropoiesis. This system facilitates functional analysis of specific genes in different developmental stages. 

Video: Mouse Fetal Liver Culture System to Dissect Target Gene Functions at the Early and Late Stages of Terminal Erythropoiesis

Introducing Shear Stress in the Study of Bacterial Adhesion

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the initial and determining step of the pathogenesis. Although experimentally adhesion is mostly studied in static conditions adhesion actually takes place in the presence of flowing liquid. First encounters between bacteria and their host often occur at the mucosal level, mouth, lung, gut, eye, etc. where mucus flows along the surface of epithelial cells. Later in infection, pathogens occasionally access the blood circulation causing life-threatening illnesses such as septicemia, sepsis and meningitis. A defining feature of these infections is the ability of these pathogens to interact with endothelial cells in presence of circulating blood. The presence of flowing liquid, mucus or blood for instance, determines adhesion because it generates a mechanical force on the pathogen. To characterize the effect of flowing liquid one usually refers to the notion of shear stress, which is the tangential force exerted per unit area by a fluid moving near a stationary wall, expressed in dynes/cm2. Intensities of shear stress vary widely according to the different vessels type, size, organ, location etc. (0-100 dynes/cm2). Circulation in capillaries can reach very low shear stress values and even temporarily stop during periods ranging between a few seconds to several minutes 1. On the other end of the spectrum shear stress in arterioles can reach 100 dynes/cm2 2. The impact of shear stress on different biological processes has been clearly demonstrated as for instance during the interaction of leukocytes with the endothelium 3. To take into account this mechanical parameter in the process of bacterial adhesion we took advantage of an experimental procedure based on the use of a disposable flow chamber 4. Host cells are grown in the flow chamber and fluorescent bacteria are introduced in the flow controlled by a syringe pump. We initially focused our investigations on the bacterial pathogen Neisseria meningitidis, a Gram-negative bacterium responsible for septicemia and meningitis. The procedure described here allowed us to study the impact of shear stress on the ability of the bacteria to: adhere to cells 1, to proliferate on the cell surface 5and to detach to colonize new sites 6 (Figure 1). Complementary technical information can be found in reference 7. Shear stress values presented here were chosen based on our previous experience1 and to represent values found in the literature. The protocol should be applicable to a wide range of pathogens with specific adjustments depending on the objectives of the study.

During the infection process, a key step is the adhesion of pathogens with host cells. In most instances this adhesion step occurs in the presence of mechanical stress generated by flowing liquid. We describe a technique that introduces shear stress as an important parameter in the study of bacterial adhesion.

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the ...

Using the BLT Humanized Mouse as a Stem Cell based Gene Therapy Tumor Model

Small animal models such as mice have been extensively used to study human disease and to develop new therapeutic interventions. Despite the wealth of information gained from these studies, the unique characteristics of mouse immunity as well as the species specificity of viral diseases such as human immunodeficiency virus (HIV) infection led to the development of humanized mouse models. The earlier models involved the use of C. B 17 scid/scid mice and the transplantation of human fetal thymus and fetal liver termed thy/liv (SCID-hu) 1, 2 or the adoptive transfer of human peripheral blood leukocytes (SCID-huPBL) 3. Both models were mainly utilized for the study of HIV infection.
One of the main limitations of both of these models was the lack of stable reconstitution of human immune cells in the periphery to make them a more physiologically relevant model to study HIV disease. To this end, the BLT humanized mouse model was developed. BLT stands for bone marrow/liver/thymus. In this model, 6 to 8 week old NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) immunocompromised mice receive the thy/liv implant as in the SCID-hu mouse model only to be followed by a second human hematopoietic stem cell transplant 4. The advantage of this system is the full reconstitution of the human immune system in the periphery. This model has been used to study HIV infection and latency 5-8.
We have generated a modified version of this model in which we use genetically modified human hematopoietic stem cells (hHSC) to construct the thy/liv implant followed by injection of transduced autologous hHSC 7, 9. This approach results in the generation of genetically modified lineages. More importantly, we adapted this system to examine the potential of generating functional cytotoxic T cells (CTL) expressing a melanoma specific T cell receptor. Using this model we were able to assess the functionality of our transgenic CTL utilizing live positron emission tomography (PET) imaging to determine tumor regression (9).
The goal of this protocol is to describe the process of generating these transgenic mice and assessing in vivo efficacy using live PET imaging. As a note, since we use human tissues and lentiviral vectors, our facilities conform to CDC NIH guidelines for Biosafety Level 2 (BSL2) with special precautions (BSL2+). In addition, the NSG mice are severely immunocompromised thus, their housing and maintenance must conform to the highest health standards (<a href="http://jaxmice.jax.org/research/immunology/005557-housing.html" target="_blank">http://jaxmice.jax.org/research/immunology/005557-housing.html</a>).

The generation and characterization of tumor specific T cells using humanized mice is described here. Human thymic tissue and genetically modified human hematopoietic stem cells are transplanted into immunocompromised mice. This results in the reconstitution of an engineered human immune system allowing for in vivo examination of anti-tumor immune responses.

Small animal models such as mice have been extensively used to study human  disease and to develop new therapeutic interventions. Despite the wealth of  ...

Multi-target Parallel Processing Approach for Gene-to-structure Determination of the Influenza Polymerase PB2 Subunit

Pandemic outbreaks of highly virulent influenza strains can cause widespread morbidity and mortality in human populations worldwide. In the United States alone, an average of 41,400 deaths and 1.86 million hospitalizations are caused by influenza virus infection each year 1. Point mutations in the polymerase basic protein 2 subunit (PB2) have been linked to the adaptation of the viral infection in humans 2. Findings from such studies have revealed the biological significance of PB2 as a virulence factor, thus highlighting its potential as an antiviral drug target.
The structural genomics program put forth by the National Institute of Allergy and Infectious Disease (NIAID) provides funding to Emerald Bio and three other Pacific Northwest institutions that together make up the Seattle Structural Genomics Center for Infectious Disease (SSGCID). The SSGCID is dedicated to providing the scientific community with three-dimensional protein structures of NIAID category A-C pathogens. Making such structural information available to the scientific community serves to accelerate structure-based drug design.
Structure-based drug design plays an important role in drug development. Pursuing multiple targets in parallel greatly increases the chance of success for new lead discovery by targeting a pathway or an entire protein family. Emerald Bio has developed a high-throughput, multi-target parallel processing pipeline (MTPP) for gene-to-structure determination to support the consortium. Here we describe the protocols used to determine the structure of the PB2 subunit from four different influenza A strains.

Structure-based drug design plays an important role in drug development. Pursuing multiple targets in parallel greatly increases the chance of success for lead discovery. The following article highlights how the Seattle Structural Genomics Center for Infectious Disease utilizes a multi-target approach for gene-to-structure determination of the PB2 influenza A subunit.

Pandemic outbreaks of highly virulent influenza strains can cause widespread morbidity and mortality in human populations worldwide. In the United States ...

A Protocol for Analyzing Hepatitis C Virus Replication

Hepatitis C Virus (HCV) affects 3% of the world&#8217;s population and causes serious liver ailments including&#160;chronic hepatitis, cirrhosis, and hepatocellular carcinoma. HCV is an enveloped RNA virus belonging to the family Flaviviridae. Current treatment is not fully effective and causes adverse side effects. There is no HCV vaccine available. Thus, continued effort is required for developing a vaccine and better therapy. An HCV cell culture system is critical for studying various stages of HCV growth including viral entry, genome replication, packaging, and egress. In the current procedure presented, we used a wild-type intragenotype 2a chimeric virus, FNX-HCV, and a recombinant FNX-Rluc virus carrying a Renilla luciferase reporter gene to study the virus replication. A human hepatoma cell line (Huh-7 based) was used for transfection of in vitro transcribed HCV genomic RNAs. Cell-free culture supernatants, protein lysates and total RNA were harvested at various time points post-transfection to assess HCV growth. HCV genome replication status was evaluated by quantitative RT-PCR and visualizing the presence of HCV double-stranded RNA. The HCV protein expression was verified by Western blot and immunofluorescence assays using antibodies specific for HCV NS3 and NS5A proteins. HCV RNA transfected cells released infectious particles into culture supernatant and the viral titer was measured. Luciferase assays were utilized to assess the replication level and infectivity of reporter HCV. In conclusion, we present various virological assays for characterizing different stages of the HCV replication cycle.

Hepatitis C Virus (HCV) is a major human pathogen that causes liver disorders, including cirrhosis and cancer. An HCV infectious cell culture system is essential for understanding the molecular mechanism of HCV replication and developing new therapeutic approaches. Here we describe a protocol to investigate various stages of the HCV replication cycle.

Hepatitis C Virus (HCV) affects 3% of the world&#8217;s population and causes serious liver ailments including&#160;chronic hepatitis, cirrhosis, and ...

Vaccinia Reporter Viruses for Quantifying Viral Function at All Stages of Gene Expression

Poxviruses are a family of double stranded DNA viruses that include active human pathogens such as monkeypox, molluscum contagiousum, and Contagalo virus. The family also includes the smallpox virus, Variola. Due to the complexity of poxvirus replication, many questions still remain regarding their gene expression strategy. In this article we describe the conceptualization and usage of recombinant vaccinia viruses that enable real-time measurement of single and multiple stages of viral gene expression in a high-throughput format. This is enabled through the use of spectrally distinct fluorescent proteins as reporters for each of three stages of viral replication. These viruses provide a high signal-to-noise ratio while retaining stage specific expression patterns, enabling plate-based assays and microscopic observations of virus propagation and replication. These tools have uses for antiviral discovery, studies of the virus-host interaction, and evolutionary biology.

We describe the usage of a fluorescent reporter vaccinia virus that enables real-time measurement of viral infectivity and gene expression through the stage-specific expression of spectrally distinct reporter fluorophores. We detail a plate-based method for accurately identifying the stage at which virus replication is affected in response to small molecule inhibition.

Poxviruses are a family of double stranded DNA viruses that include active human pathogens such as monkeypox, molluscum contagiousum, and Contagalo virus. ...

Isolation of Leukocytes from the Murine Tissues at the Maternal-Fetal Interface

Immune tolerance in pregnancy requires that the immune system of the mother undergoes distinctive changes in order to accept and nurture the developing fetus. This tolerance is initiated during coitus, established during fecundation and implantation, and maintained throughout pregnancy. Active cellular and molecular mediators of maternal-fetal tolerance are enriched at the site of contact between fetal and maternal tissues, known as the maternal-fetal interface, which includes the placenta and the uterine and decidual tissues. This interface is comprised of stromal cells and infiltrating leukocytes, and their abundance and phenotypic characteristics change over the course of pregnancy. Infiltrating leukocytes at the maternal-fetal interface include neutrophils, macrophages, dendritic cells, mast cells, T cells, B cells, NK cells, and NKT cells that together create the local micro-environment that sustains pregnancy. An imbalance among these cells or any inappropriate alteration in their phenotypes is considered a mechanism of disease in pregnancy. Therefore, the study of leukocytes that infiltrate the maternal-fetal interface is essential in order to elucidate the immune mechanisms that lead to pregnancy-related complications. Described herein is a protocol that uses a combination of gentle mechanical dissociation followed by a robust enzymatic disaggregation with a proteolytic and collagenolytic enzymatic cocktail to isolate the infiltrating leukocytes from the murine tissues at the maternal-fetal interface. This protocol allows for the isolation of high numbers of viable leukocytes (&#62;70%) with sufficiently conserved antigenic and functional properties. Isolated leukocytes can then be analyzed by several techniques, including immunophenotyping, cell sorting, imaging, immunoblotting, mRNA expression, cell culture, and in vitro functional assays such as mixed leukocyte reactions, proliferation, or cytotoxicity assays.

Described herein is a protocol to isolate and analyze the infiltrating leukocytes of tissues at the maternal-fetal interface (uterus, decidua, and placenta) of mice. This protocol maintains the integrity of most cell surface markers and yields enough viable cells for downstream applications including flow cytometry analysis.

Immune tolerance in pregnancy requires that the immune system of the mother undergoes distinctive changes in order to accept and nurture the developing ...

Human Placental and Decidual Organ Cultures to Study Infections at the Maternal-fetal Interface

The placenta shows a large degree of interspecies anatomic variability. To best understand biology and pathophysiology of the human placenta, it is imperative to design experiments using human cells and tissues. An advantage of organ culture is maintenance of three-dimensional (3D) structural organization and extracellular matrix. The goal of the method described here is successful establishment of ex vivo human gestational tissue organ cultures and their healthy culture maintenance for 72-96 hr. The protocol details the immediate processing of research-consented, placental and decidual specimens fresh from the operating suite. These are abundant specimens that would otherwise be discarded. Detailed instructions on the sterile collection of these samples, including morphologic details on how to select appropriate tissues to establish 3D organ cultures, is provided. Placental villous and decidual tissues are microdissected into 2-3 mm3 pieces and placed separately on matrix-lined transwell filters and cultured for several days. Villous and decidual organ cultures are well suited for the study of human host-pathogen interaction. As compared to other model organisms, these human cultures are particularly advantageous to examine mechanism of infection for pathogens that demonstrate variable patterns of host specificity. As an example, we demonstrate infection of placental and decidual organ cultures with the clinically relevant, facultative intracellular bacterial pathogen Listeria monocytogenes.

A simple method to establish primary human placental (villous) and decidual organ cultures is described. Villous and decidual organ cultures are invaluable tools for studying pathogenesis at the human maternal-fetal interface. Infection with the facultative intracellular bacterium Listeria monocytogenes is demonstrated.

The placenta shows a large degree of interspecies anatomic variability. To best understand biology and pathophysiology of the human placenta, it is ...

Flow Cytometry-based Assay for the Monitoring of NK Cell Functions

Natural killer (NK) cells are an important part of the human tumor immune surveillance system. NK cells are able to distinguish between healthy and virus-infected or malignantly transformed cells due to a set of germline encoded inhibitory and activating receptors. Upon virus or tumor cell recognition a variety of different NK cell functions are initiated including cytotoxicity against the target cell as well as cytokine and chemokine production leading to the activation of other immune cells. It has been demonstrated that accurate NK cell functions are crucial for the treatment outcome of different virus infections and malignant diseases. Here a simple and reliable method is described to analyze different NK cell functions using a flow cytometry-based assay. NK cell functions can be evaluated not only for the whole NK cell population, but also for different NK cell subsets. This technique enables scientists to easily study NK cell functions in healthy donors or patients in order to reveal their impact on different malignancies and to further discover new therapeutic strategies.

A simple and reliable method is described here to analyze a set of NK cell functions such as degranulation, cytokine and chemokine production within different NK cell subsets.

Natural killer (NK) cells are an important part of the human tumor immune surveillance system. NK cells are able to distinguish between healthy and ...

Development of a Hepatitis B Virus Reporter System to Monitor the Early Stages of the Replication Cycle

Currently, it is possible to construct recombinant forms of various viruses, such as human immunodeficiency virus 1 (HIV-1) and hepatitis C virus (HCV), that carry foreign genes such as a reporter or marker protein in their genomes. These recombinant viruses usually faithfully mimic the life cycle of the original virus in infected cells and exhibit the same host range dependence. The development of a recombinant virus enables the efficient screening of inhibitors and the identification of specific host factors. However, to date the construction of recombinant hepatitis B virus (HBV) has been difficult because of various experimental limitations. The main limitation is the compact genome size of HBV, and a fairly strict genome size that does not exceed 1.3 genome sizes, that must be packaged into virions. Thus, the size of a foreign gene to be inserted should be smaller than 0.4 kb if no deletion of the genome DNA is to be performed. Therefore, to overcome this size limitation, the deletion of some HBV DNA is required. Here, we report the construction of recombinant HBV encoding a reporter gene to monitor the early stage of the HBV replication cycle by replacing part of the HBV core-coding region with the reporter gene by deleting part of the HBV pol coding region. Detection of recombinant HBV infection, monitored by the reporter activity, was highly sensitive and less expensive than detection using the currently available conventional methods to evaluate HBV infection. This system will be useful for a number of applications including high-throughput screening for the identification of anti-HBV inhibitors, host factors and virus-susceptible cells.

Here we describe a newly developed hepatitis B virus (HBV) reporter system to monitor the early stages of the HBV life cycle. This simplified in vitro system will aid in the screening of anti-HBV agents using a high-throughput strategy.

Currently, it is possible to construct recombinant forms of various viruses, such as human immunodeficiency virus 1 (HIV-1) and hepatitis C virus (HCV), ...

Generation of Escape Variants of Neutralizing Influenza Virus Monoclonal Antibodies

Influenza viruses exhibit a remarkable ability to adapt and evade the host immune response. One way is through antigenic changes that occur on the surface glycoproteins of the virus. The generation of escape variants is a powerful method in elucidating how viruses escape immune detection and in identifying critical residues required for antibody binding. Here, we describe a protocol on how to generate influenza A virus escape variants by utilizing human or murine monoclonal antibodies (mAbs) directed against the viral hemagglutinin (HA). With the use of our technique, we previously characterized critical residues required for the binding of antibodies targeting either the head or stalk of the novel avian H7N9 HA. The protocol can be easily adapted for other virus systems. Analyses of escape variants are important for modeling antigenic drift, determining single nucleotide polymorphisms (SNPs) conferring resistance and virus fitness, and in the designing of vaccines and/or therapeutics.

We describe a method by which we identify critical residues required for the binding of human or murine monoclonal antibodies that target the viral hemagglutinin of influenza A viruses. The protocol can be adapted to other virus surface glycoproteins and their corresponding neutralizing antibodies.

Influenza viruses exhibit a remarkable ability to adapt and evade the host immune response. One way is through antigenic changes that occur on the surface ...