We thank the Dictyostelium Stock Center for strains and reagents. This study was financed by grants from the Swiss National Science Foundation and the Canton of Basel.

<ol>
	<li>Observe the early starvation response of Dictyostelium discoideum by time-lapse microscopy.
	<ol>
		<li>Grow DH1.10 cells or corA-deficient cells in an Erlenmayer flask containing HL-5 medium (for 1 L: 5 g proteose peptone, 5 g thiotone E peptone, 10 g glucose, 5 g yeast extract, 0.35 g Na2HPO4*7H2O, 0.35 g KH2PO4, 0.05 g dihydrostreptomycin-sulfate, pH 6.6) at 22 &#176;C in a shaking incubator with a rotation of 160 rpm. Keep cells at a density between 0.01 x 106 cells/ml and 2 x 106 cells/ml.</li>
		<li>Examine cell aggregation, by harvesting log-phase-growing DH1.10 cells21 or corA-deficient cells10 generated in the DH1.10 background, grown in shaking culture with HL-5 medium at 22 &#176;C. To do so, take appropriate amount of cells (usually between 10 and 50 ml), centrifuge for 3 min at 400 x g and wash the cells twice in BSS (10 mM NaCl, 10 mM KCl, 2.5 mM CaCl2, pH 6.5).</li>
		<li>Count cells using a hemocytometer. Subsequently, plate cells at a density of (5, 10, 20, or 40) x 104 cells/cm2 in a 24-well plate. Allow them to adhere for 1 hr at 22 &#176;C in BSS.</li>
		<li>Visualize aggregation by time-lapse microscopy as described before10, taking images every 135 sec. using a live cell imaging set up equipped with 5X objective and an electron-multiplying charge-coupled device camera automated by the appropriate software (see Materials Table).</li>
	</ol>
	</li>
	<li>cAMP pulsing of Dictyostelium discoideum cells during starvation.
	<ol>
		<li>Examine the effect of externally applied cAMP pulses on the development of DH1.10 cells21 or DH1.10 corA-deficient cells10, by harvesting cells. To do so, take appropriate amount of cells (usually between 10 and 50 ml), centrifuge for 3 min at 400 x g and wash twice in BSS.</li>
		<li>Count cells using a hemocytometer and resuspend the cells to a density of 1 x 107 cells/ml in BSS. Shake the cultures (160 rpm) at 22 &#176;C for 2 hr before applying pulses. Add cAMP pulses using a timer controlled peristaltic pump. Program the pump to deliver a 5 sec pulse every 6.5 min of 15 &#181;l of 50 nM cAMP (final concentration) over a period of 5 hr.</li>
		<li>Count cells using a hemocytometer. Subsequently, plate the cells at a density of (5, 10, 20, or 40) x 104 cells/cm2 in a 24-well plate. Allow to adhere for 1 hr in BSS.</li>
		<li>Visualize aggregation after 16 hr at 22 &#176;C by bright-field microscopy using a 5X objective.</li>
	</ol>
	</li>
	<li>Induction of Dictyostelium discoideum development through exposure to conditioned medium.
	<ol>
		<li>Prepare fresh conditioned medium as described22. Collect log-phase DH1.10 cells21 or DH1.10 corA-deficient cells10, from shaking cultures with HL-5 medium at 22 &#176;C using a pipette, centrifuge for 3 min at 400 x g and wash cells three times in PBM (0.02 M potassium phosphate, 10 &#181;M CaCl2, and 1 mM MgCl2, pH 6.1).</li>
		<li>Count cells using a hemocytometer, resuspend these in PBM at a density of 1 x 107 cells/ml and shake for 20 hr at 110 rpm/22 &#176;C.</li>
		<li>Collect conditioned medium after centrifugation at 400 &#215; g for 3 min and clarify by centrifugation at 8,000 &#215; g for 15 min at 4&#176;C.</li>
		<li>Filter conditioned medium through a 0.45 &#181;m filter (see Materials Table) and dilute threefold in PBM.</li>
		<li>Count cells using a hemocytometer and plate at a density of (5, 10, 20, or 40) x 104 cells/cm2 in a 24-well plate. Allow them to adhere for 1 hr at 22 &#176;C.</li>
		<li>Exchange supernatant of the cells with the previously prepared conditioned medium.</li>
		<li>Visualize aggregation after 16 hr by bright-field microscopy using a 5X objective.</li>
	</ol>
	</li>
</ol>

<ol>
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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=cAMP+signal+transduction+pathways+regulating+development+of+Dictyostelium+discoideum.">cAMP signal transduction pathways regulating development of Dictyostelium discoideum.</a> Curr Opin Genet Dev. 1, 383-390 (1991).</li><li>Clarke, M., Gomer, R. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PSF+and+CMF,+autocrine+factors+that+regulate+gene+expression+during+growth+and+early+development+of+Dictyostelium.">PSF and CMF, autocrine factors that regulate gene expression during growth and early development of Dictyostelium.</a> Experientia. 51, 1124-1134 (1995).</li><li>Robertson, A., Drage, D. J., Cohen, M. 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F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genome-wide+expression+analyses+of+gene+regulation+during+early+development+of+Dictyostelium+discoideum.">Genome-wide expression analyses of gene regulation during early development of Dictyostelium discoideum.</a> Eukaryot Cell. 2, 664-670 (2003).</li><li>Darmon, M., Brachet, P., Da Silva, L. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemotactic+signals+induce+cell+differentiation+in+Dictyostelium+discoideum.">Chemotactic signals induce cell differentiation in Dictyostelium discoideum.</a> Proc Natl Acad Sci U S A. 72, 3163-3166 (1975).</li><li>Mann, S. K., Firtel, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cyclic+AMP+regulation+of+early+gene+expression+in+Dictyostelium+discoideum:+mediation+via+the+cell+surface+cyclic+AMP+receptor.">Cyclic AMP regulation of early gene expression in Dictyostelium discoideum: mediation via the cell surface cyclic AMP receptor.</a> Mol Cell Biol. 7, 458-469 (1987).</li><li>Vinet, A. F., 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=Initiation+of+multicellular+differentiation+in+Dictyostelium+discoideum+is+regulated+by+coronin+A.">Initiation of multicellular differentiation in Dictyostelium discoideum is regulated by coronin A.</a> Mol Biol Cell. 25, 688-701 (2014).</li><li>Eckert, C., Hammesfahr, B., Kollmar, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+holistic+phylogeny+of+the+coronin+gene+family+reveals+an+ancient+origin+of+the+tandem-coronin,+defines+a+new+subfamily,+and+predicts+protein+function.">A holistic phylogeny of the coronin gene family reveals an ancient origin of the tandem-coronin, defines a new subfamily, and predicts protein function.</a> BMC Evol Biol. 11, 268 (2011).</li><li>Pieters, J., Muller, P., Jayachandran, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+guard:+coronin+proteins+in+innate+and+adaptive+immunity.">On guard: coronin proteins in innate and adaptive immunity.</a> Nat Rev Immunol. 13, 510-518 (2013).</li><li>Gatfield, J., Albrecht, I., Zanolari, B., Steinmetz, M. O., Pieters, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Association+of+the+Leukocyte+Plasma+Membrane+with+the+Actin+Cytoskeleton+through+Coiled+Coil-mediated+Trimeric+Coronin+1+Molecules.">Association of the Leukocyte Plasma Membrane with the Actin Cytoskeleton through Coiled Coil-mediated Trimeric Coronin 1 Molecules.</a> Mol Biol Cell. 16, 2786-2798 (2005).</li><li>Kammerer, R. A., 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=A+conserved+trimerization+motif+controls+the+topology+of+short+coiled+coils.">A conserved trimerization motif controls the topology of short coiled coils.</a> Proc Natl Acad Sci U S A. 102, 13891-13896 (2005).</li><li>Uetrecht, A. C., Bear, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coronins:+the+return+of+the+crown.">Coronins: the return of the crown.</a> Trends Cell Biol. 16, 421-426 (2006).</li><li>Jayachandran, R., 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=Coronin+1+Regulates+Cognition+and+Behavior+through+Modulation+of+cAMP/Protein+Kinase+A+Signaling.">Coronin 1 Regulates Cognition and Behavior through Modulation of cAMP/Protein Kinase A Signaling.</a> PLoS Biol. 12, e1001820 (2014).</li><li>Suo, D., 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=Coronin-1+is+a+neurotrophin+endosomal+effector+that+is+required+for+developmental+competition+for+survival.">Coronin-1 is a neurotrophin endosomal effector that is required for developmental competition for survival.</a> Nat Neurosci. 17, 36-45 (2014).</li><li>Mueller, P., 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=Regulation+of+T+cell+survival+through+coronin-1-mediated+generation+of+inositol-1,4,5-trisphosphate+and+calcium+mobilization+after+T+cell+receptor+triggering.">Regulation of T cell survival through coronin-1-mediated generation of inositol-1,4,5-trisphosphate and calcium mobilization after T cell receptor triggering.</a> Nat Immunol. 9, 424-431 (2008).</li><li>de Hostos, E. L., Bradtke, B., Lottspeich, F., Guggenheim, R., Gerisch, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coronin,+an+actin+binding+protein+of+Dictyostelium+discoideum+localized+to+cell+surface+projections,+has+sequence+similarities+to+G+protein+beta+subunits.">Coronin, an actin binding protein of Dictyostelium discoideum localized to cell surface projections, has sequence similarities to G protein beta subunits.</a> EMBO J. 10, 4097-4104 (1991).</li><li>Shina, M. 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No conflicts of interest declared.

The coronin proteins are found in most taxa of the eukaryotic clade. Dictyostelium discoideum coronin A, the homologue of mammalian coronin 1, is involved in the early starvation response, since coronin A-deficient cells are not able to form aggregation centers during the early developmental cycle10. To be able to quantitatively and accurately assess the delay in development between the strains, a microscope live cell imaging set-up with the automated stage controller is an essential tool.
D. discoideum utilizes cAMP as an essential signaling molecule during several stages of its life cycle1-4. One of the checkpoints during which cAMP is required is the transition from a single cell to the formation of multicellular structures. The onset of cAMP waves after ~6 hr of starvation is sensed by the cells and provides the chemotactic signal to move towards an aggregation center5. These cAMP waves can be mimicked experimentally by pulsing starving D. discoideum cells with cAMP every 6.5 min over a period of 5h8,9. Using this procedure it is important to starve the cells for up to 2h before applying the cAMP pulses, in order to obtain reliable results. Utilizing this experimental set up we were able to show that coronin A is acting upstream of cAMP signaling, as these externally applied pulses rescued the development in corA-deficient cells (Figure 3 and 5). These results also indicate that while coronin A appears to have an essential role in sensing the early starvation response, it is dispensable for processes such as chemotaxis and cell aggregation per se10.
The aggregation assay itself is a robust method for studying the early development of Dictyostelium discoideum. However, there are several pitfalls that can influence the reproducibility of these experiments, and it is therefore important that several factors are taken into account: the age of the cells plays an important role when analyzing corA-deficient cells. These cells tend to compensate the phenotype and re-aggregate approximately after 2 weeks from the point they are thawed. The density of the cells is a crucial factor as well, as cells that show a signaling defect and not a chemotactic defect might tend to aggregate at higher densities due to the increased concentration of early starvation factors. The importance of the precise counting and dilution of cells in these assays cannot be overstated. For different strains, an adjustment of multiple variables of the assay, such as cell densities, time of adherence, time of development, will be required. The aggregation assay as described here is a versatile technique that can be modified to suit different inquiries: the cells can be starved, or development can be stimulated or inhibited using different compounds, allowing for a specific modulation of aggregation. The here described set-up also allows for unbiased approaches to identify strains with early developmental defects, as well as for the identification of genes or factors which are important for early development. This is also the method&#39;s major drawback: the aggregation assay is a reduced version of the complete developmental cycle. Therefore, it is not suitable for the analysis of phenotypes affecting later stages of the developmental cycle. The main advantage is the possibility to adopt the aggregation assay to a large scale and automated format: in 48-well plates and with 16 hr of development recorded during automated imaging, the aggregation assay proves to be more time and resource-efficient than development on agar plates.
In experiments in which we bypassed the early starvation response, using externally applied cAMP pulses, we showed that coronin A is involved in the sensing of secreted factors by Dictyostelium cells upon starvation. The precise mechanism of coronin A-mediated signaling during the early starvation response remains unclear. Several factors involved during this stage of development have been studied, in particular conditioned medium factor (CMF)25,26. However, whether CMF acts on its own or with co-factors remains unclear and its signaling cascade is only partially understood. Using the aggregation capacity of Dictyostelium cells under submerged conditions here described as a positive read-out for development allows to conduct large-scale screening experiments in a time-efficient manner as compared to aggregation assays on agar surfaces. However, aggregation assays under submerged conditions do have the disadvantage of not fulfilling the complete developmental cycle as cells will be arrested in the initial aggregation stage. Therefore, the technique described here is not suitable for the examination of later developmental processes. In summary, the experimental approach documented here may allow further characterization of potential early starvation factor(s) that induce coronin A-dependent entry into the early starvation response.

The coronin family of proteins is highly conserved throughout eukaryotes. These proteins are characterized by the presence of an amino-terminal tryptophan-aspartate (WD) repeat-containing region followed by a unique region connected to a carboxy-terminal coiled-coil domain13,14 (Figure 1). Coronins have been implicated in a variety of cellular functions, including cytoskeletal regulation and signal transduction12. In mammals, up to six short coronin molecules (coronin 1-6) as well as a &#39;tandem&#39; coronin 7, can be co-expressed12,15. Coronin 1 is the most extensively studied family member, and was shown to be involved in pathogen destruction, T cell survival and neuronal signaling. How, exactly, coronin 1 carries out these activities remains unclear. While coronin 1 was shown to regulate Ca2+ and cAMP-dependent signaling as well as F-actin cytoskeleton modulation 16-18, the potential co-expression of up to 7 family members in mammals has made it challenging to study the molecular function of coronins in these systems, due to potential redundancies. Unlike mammalian organisms, the lower eukaryote Dictyostelium discoideum expresses only two coronin family members (coronin A, the ortholog of mammalian coronin 1 and coronin B, the ortholog of mammalian coronin 7) with apparently non-redundant functions15,19,20. This fact makes Dictyostelium discoideum a potent model to study the function of coronins.
To study the role of coronin A in Dictyostelium discoideum, we induced the developmental cycle by starvation in tissue-culture plates containing balanced salt solution (BSS) buffer using either wild type cells or cells lacking coronin A10. We found that cells lacking coronin A were unable to form multicellular aggregates upon starvation. For an accurate quantitative assessment of this phenotype the automated live cell imaging described in this protocol is a vital tool. The defect in the initiation of the early starvation response in cells lacking coronin A can be rescued by supplying pulses of cAMP, suggesting that coronin A acts upstream of the cAMP cascade. The exogenous application of cAMP pulses to simulate the initiation of development has been utilized by several laboratories in the past8,9. However, this procedure is also known to be highly dependent on cell densities and timing. Therefore, the protocol described here aims to reduce these variabilities in order to guarantee a high degree of reproducibility. Taken together, the techniques utilized in these studies provide robust tools to investigate functions of proteins during early stages of the developmental cycle of Dictyostelium discoideum and have the potential to identify up- as well as downstream effectors of coronin A function.

<table>
	<tbody>
		<tr>
			<td>HL-5 media (for 1L: 5 g proteose peptone, 5 g thiotone E peptone, 10 g glucose, 5 g yeast extract, 0.35 g Na2HPO4&#8727;2H2O, 0.35 g KH2PO4, 0.05 g dihydrostreptomycin-sulfate, pH 6.6)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Proteose peptone</td>
			<td>BD Bioscience</td>
			<td>211693</td>
			<td></td>
		</tr>
		<tr>
			<td>Thiotone E peptone</td>
			<td>BD Bioscience</td>
			<td>211684</td>
			<td></td>
		</tr>
		<tr>
			<td>Yeast extract</td>
			<td>BD Bioscience</td>
			<td>212750</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>AppliChem</td>
			<td>A3666</td>
			<td></td>
		</tr>
		<tr>
			<td>Na2HPO4&#8727;2H2O</td>
			<td>Fluka</td>
			<td>71643</td>
			<td></td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>AppliChem</td>
			<td>A1043</td>
			<td></td>
		</tr>
		<tr>
			<td>dihydrostreptomycin-sulfate</td>
			<td>Sigma-Aldrich</td>
			<td>D1954000</td>
			<td></td>
		</tr>
		<tr>
			<td>PBM (0.02 M potassium phosphate, 10 &#956;M CaCl2, and l mM MgCl2, pH 6.1)</td>
			<td></td>
			<td></td>
			<td>self made</td>
		</tr>
		<tr>
			<td>BSS (10 mM NaCl, 10 mM KCl, 2.5 mM CaCl2, pH 6.5)</td>
			<td></td>
			<td></td>
			<td>self made</td>
		</tr>
		<tr>
			<td>0.45-&#956;m Filtropure S filter</td>
			<td>Sarstedt</td>
			<td>83.1826</td>
			<td></td>
		</tr>
		<tr>
			<td>Falcon 24-well Tissue culture plate</td>
			<td>Fisher Scientific</td>
			<td><a href="https://www.fishersci.com/shop/products/falcon-tissue-culture-plates-23/087721h">08-772-1H</a></td>
			<td></td>
		</tr>
		<tr>
			<td>Cellobserver microscope</td>
			<td>Zeiss</td>
			<td></td>
			<td>custom built</td>
		</tr>
		<tr>
			<td>AxioVision software</td>
			<td>Zeiss</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>IPC Microprocessor&#8211;controlled dispensing pump</td>
			<td>ISMATEC</td>
			<td>ISM 931</td>
			<td></td>
		</tr>
		<tr>
			<td>Axiovert 135M microscope</td>
			<td>Zeiss</td>
			<td>491237-0001-000</td>
			<td></td>
		</tr>
		<tr>
			<td>Incubation Shaker</td>
			<td>Inforst HT Minitron</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

investigating the function of coronin a in the early starvation response of dictyostelium discoideum by aggregation assays

Dictyostelium discoideum amoeba are found in soil, feeding on bacteria. When food sources become scarce, they secrete factors to initiate a multicellular development program, during which single cells chemotax towards aggregation centers1-4. This process is dependent on the release of cyclic adenosine monophosphate (cAMP)5. cAMP is produced in waves through the concerted action of adenylate cyclase and phosphodiesterases, and binds to G protein-coupled cAMP receptors6,7. A widely used assay to analyze the mechanisms involved in the developmental cycle of the lower eukaryote Dictyostelium discoideum is based on the observation of cell aggregation in submerged conditions8,9. This protocol describes the analysis of the role of coronin A in the developmental cycle by starvation in tissue-culture plates submerged in balanced salt solution (BSS)10. Coronin A is a member of the widely conserved protein family of coronins that have been implicated in a wide variety of activities11,12. Dictyostelium cells lacking coronin A are unable to form multicellular aggregates, and this defect can be rescued by supplying pulses of cAMP, suggesting that coronin A acts upstream of the cAMP cascade10. The techniques described in these studies provide robust tools to investigate functions of proteins during the initial stages of the developmental cycle of Dictyostelium discoideum upstream of the cAMP cascade. Therefore, utilizing this aggregation assay may allow the further study of coronin A function and advance our understanding of coronin biology.

Cells deficient in coronin A show a defect in early development (Figure 2). In the absence of coronin A cells are unable to form multicellular aggregates, which is the initial step during the developmental cycle of Dictyostelium discoideum. Therefore, coronin A appears to play a role during the early starvation response and/or cAMP signaling. Indeed, the lack of multicellular aggregate formation in the absence of coronin A is accompanied by reduced cAMP signaling 10. However, the application of exogenous cAMP pulses fully restores the wild-type phenotype (Figure 3). This implicates that coronin A, rather than being directly involved in cAMP signaling, functions upstream of the cAMP cascade (Figure 5). When Dictyostelium cells are exposed to starving conditions they induce the secretion of early starvation factors22,23. One of the best characterized factors involved in the early starvation response is conditioned medium factor (CMF)22. Based on our results, we hypothesized that coronin A either regulates the secretion of these early starvation factors or is involved in the signal transduction induced by these factors. In order to be able to differentiate between these two effects we performed conditioned medium experiments. Wild-type or corA-deficient cells were exposed to supernatants from either starved wild-type or corA-deficient cells10 (Figure 4). These supernatants are potent initiators of multicellular aggregate formation and therefore contain factors that initiate downstream developmental signaling pathways, including cAMP signaling. Our results show that supernatant from corA-deficient cells was equally capable to induce development as was the case for supernatant from wild-type cells (Figure 4). This implicates that corA-deficient cells are able to produce and secrete early starvation factors at similar levels to their wild-type controls. However, corA-deficient cells are neither able to respond to their own supernatant nor to supernatant provided from wild-type cells (Figure 4). Therefore, coronin A appears to be involved in signaling pathways induced by early starvation factors, rather than their expression/secretion10 (Figure 5).
In general, to be able to further investigate the signals secreted by starving Dictyostelium cells that induce the developmental cycle, the aggregation assay under submerged conditions is a potent read-out. Cells seeded at higher densities will spontaneously aggregate due to an abundance of all required signals. However, at lower densities only the addition of conditioned medium will induce cellular aggregation (Figure 4)22,24. Therefore, this procedure can be utilized to fractionate conditioned medium and study distinct components for their activity during the early starvation response.
<img alt="Figure 1" src="/files/ftp_upload/53972/53972fig1.jpg" /> 
Figure 1: Coronin proteins present in mammals and Dictyostelium discoideum. The coronin family is characterized by the presence of N-terminal WD-repeat regions followed by a unique domain and a C-terminal coiled coil region. While mammals express 7 coronin proteins (A), Dictyostelium discoideum only contains two family members (B), making the risk of redundancy less likely when studying their function. Coronin A is the ortholog of mammalian coronin 1 and coronin B shows a similar domain structure as coronin 7. Abbreviations: CC, coiled-coil domain; UD, unique domain; WD repeats, tryptophan-aspartate repeats. Length is given for mouse sequences (A) in amino acids (aa). Modified from Pieters et al., 201312. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53972/53972fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/53972/53972fig2.jpg" /> 
Figure 2: corA-Dictyostelium discoideum are unable to aggregate during the early starvation response. Wild-type (A) or corA-deficient (B) Dictyostelium cells were seeded into multiwell plates at a density of 2 x 105 cells/cm2, starved in BSS, and imaged over a period of 20 hr. Scale bar = 100 &#181;m. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53972/53972fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/53972/53972fig3.jpg" /> 
Figure 3: Externally applied cAMP pulses rescue the early developmental defect of corA-Dictyostelium discoideum. Vegetative wild-type (A and B) and corA-deficient cells (C and D) were washed and starved for 2 hr&#160;before being pulsed with (B and D) or without (A and C) 50 nM cAMP during 5 hr every 6.5 min in suspension. Cells were then washed, resuspended in BSS, and placed on a Petri dish at a density of 10 x 104 cells/cm2. Images were taken 20 hr after seeding of the cells. Scale bar = 100 &#181;m. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53972/53972fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/53972/53972fig4.jpg" /> 
Figure 4: corA-deficient Dictyostelium discoideum are able to produce all required factors for developmental induction but are unable to respond to them. Exponentially growing wild-type and corA-deficient cells were washed in PBM and seeded into multiwell plates at a density of (5, 10, 20, or 40) x 104 cells/cm2, incubated in conditioned medium obtained from wild-type (A) or corA-deficient starving cells (B). The images were taken 16 hr after seeding the cells. Scale bar = 100 &#181;m. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53972/53972fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/53972/53972fig5.jpg" /> 
Figure 5: Current model of Coronin A function in Dictyostelium discoideum. Coronin A is involved in the signal transduction of factor(s) secreted during the early starvation response leading to the induction of the cAMP cascade and the progression through the developmental cycle. Modified from Vinet et al., 201410. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53972/53972fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Investigating the Function of Coronin A in the Early Starvation Response of Dictyostelium discoideum by Aggregation Assays at JoVE.com

Investigating the Function of Coronin A in the Early Starvation Response of Dictyostelium discoideum by Aggregation Assays

The social amoeba Dictyostelium discoideum undergoes a developmental transition into a multicellular organism when starved. The evolutionary conserved protein coronin A plays a crucial role in the initiation of development. Using aggregation assays as our main method, we aim to elucidate the role of coronin A in early development.

Investigating the Function of Coronin A in the Early Starvation Response of Dictyostelium discoideum by Aggregation Assays

Dictyostelium discoideum amoeba are found in soil, feeding on bacteria. When food sources become scarce, they secrete factors to initiate a multicellular ...

investigating-function-coronin-early-starvation-response

Nanyang Technological University

Research

JoVE Journal

Biology

7.2K Views.  University of Basel. The social amoeba Dictyostelium discoideum undergoes a developmental transition into a multicellular organism when starved. The evolutionary conserved protein coronin A plays a crucial role in the initiation of development. Using aggregation assays as our main method, we aim to elucidate the role of coronin A in early development.

Video: Investigating the Function of Coronin A in the Early Starvation Response of Dictyostelium discoideum by Aggregation Assays

Investigating the Microbial Community in the Termite Hindgut - Interview

Jared Leadbetter explains why the termite-gut microbial community is an excellent system for studying the complex interactions between microbes.     The symbiotic relationship existing between the host insect and lignocellulose-degrading gut microbes is explained, as well as the industrial uses of these microbes for degrading plant biomass and generating biofuels.

Jared Leadbetter explains why the termite-gut microbial community is an excellent system for studying the complex interactions between microbes. The symbiotic relationship existing between the host insect and lignocellulose-degrading gut microbes is explained, as well as the industrial uses of these microbes for degrading plant biomass and generating biofuels.

Jared Leadbetter explains why the termite-gut microbial community is an excellent system for studying the complex interactions between microbes.     The ...

Using the optokinetic response to study visual function of zebrafish

Optokinetic response (OKR) is a behavior that an animal vibrates its eyes to follow a rotating grating around it. It has been widely used to assess the visual functions of larval zebrafish1-5. Nevertheless, the standard protocol for larval fish is not yet readily applicable in adult zabrafish. Here, we introduce how to measure the OKR of adult zebrafish with our simple custom-built apparatus using a new protocol which is established in our lab. Both our apparatus and step-by-step procedure of OKR in adult zebrafish are illustrated in this video. In addition, the measurements of the larval OKR, as well as the optomotor response (OMR) test of adult zebrafish, are also demonstrated in this video. This OKR assay of adult zebrafish in our experiment may last for up to 4 hours. Such OKR test applied in adult fish will benefit to visual function investigation more efficiently when the adult fish vision system is manipulated.
Su-Qi Zou and Wu Yin contributed equally to this paper.

Optokinetic response has been widely used to assess the visual functions of larval zebrafish. Nevertheless, the standard protocol for larval fish is not yet readily applicable in adults1-5. Here, we introduce how to measure the OKR of adult zebrafish using a new protocol which is established in our lab.

Optokinetic response (OKR) is a behavior that an animal vibrates its eyes to follow a rotating grating around it. It has been widely used to assess the ...

Quantification of &gamma;H2AX Foci in Response to Ionising Radiation

DNA double-strand breaks (DSBs), which are induced by either endogenous metabolic processes or by exogenous sources, are one of the most critical DNA lesions with respect to survival and preservation of genomic integrity. An early response to the induction of DSBs is phosphorylation of the H2A histone variant, H2AX, at the serine-139 residue, in the highly conserved C-terminal SQEY motif, forming &gamma;H2AX1. Following induction of DSBs, H2AX is rapidly phosphorylated by the phosphatidyl-inosito 3-kinase (PIKK) family of proteins, ataxia telangiectasia mutated (ATM), DNA-protein kinase catalytic subunit and ATM and RAD3-related (ATR)2. Typically, only a few base-pairs (bp) are implicated in a DSB, however, there is significant signal amplification, given the importance of chromatin modifications in DNA damage signalling and repair. Phosphorylation of H2AX mediated predominantly by ATM spreads to adjacent areas of chromatin, affecting approximately 0.03% of total cellular H2AX per DSB2,3. This corresponds to phosphorylation of approximately 2000 H2AX molecules spanning ~2 Mbp regions of chromatin surrounding the site of the DSB and results in the formation of discrete &gamma;H2AX foci which can be easily visualized and quantitated by immunofluorescence microscopy2. The loss of &gamma;H2AX at DSB reflects repair, however, there is some controversy as to what defines complete repair of DSBs; it has been proposed that rejoining of both strands of DNA is adequate however, it has also been suggested that re-instatement of the original chromatin state of compaction is necessary4-8. The disappearence of &gamma;H2AX involves at least in part, dephosphorylation by phosphatases, phosphatase 2A and phosphatase 4C5,6. Further, removal of &gamma;H2AX by redistribution involving histone exchange with H2A.Z has been implicated7,8. Importantly, the quantitative analysis of &gamma;H2AX foci has led to a wide range of applications in medical and nuclear research. Here, we demonstrate the most commonly used immunofluorescence method for evaluation of initial DNA damage by detection and quantitation of &gamma;H2AX foci in &gamma;-irradiated adherent human keratinocytes9.

Quantification of &#947;H2AX Foci in Response to Ionising Radiation

Quantification of DNA double-strand streaks using &gamma;H2AX formation as a molecular marker has become an invaluable tool in radiation biology. Here we demonstrate the use of an immunofluorescence assay for quantification of &gamma;H2AX foci after exposure of cells to radiation.

DNA double-strand breaks (DSBs), which are induced by either endogenous metabolic processes or by exogenous sources, are one of the most critical DNA ...

Imaging G-protein Coupled Receptor (GPCR)-mediated Signaling Events that Control Chemotaxis of Dictyostelium Discoideum

Many eukaryotic cells can detect gradients of chemical signals in their environments and migrate accordingly 1. This guided cell migration is referred as chemotaxis, which is essential for various cells to carry out their functions such as trafficking of immune cells and patterning of neuronal cells 2, 3. A large family of G-protein coupled receptors (GPCRs) detects variable small peptides, known as chemokines, to direct cell migration in vivo 4. The final goal of chemotaxis research is to understand how a GPCR machinery senses chemokine gradients and controls signaling events leading to chemotaxis. To this end, we use imaging techniques to monitor, in real time, spatiotemporal concentrations of chemoattractants, cell movement in a gradient of chemoattractant, GPCR mediated activation of heterotrimeric G-protein, and intracellular signaling events involved in chemotaxis of eukaryotic cells 5-8. The simple eukaryotic organism, Dictyostelium discoideum, displays chemotaxic behaviors that are similar to those of leukocytes, and D. discoideum is a key model system for studying eukaryotic chemotaxis. As free-living amoebae, D. discoideum cells divide in rich medium. Upon starvation, cells enter a developmental program in which they aggregate through cAMP-mediated chemotaxis to form multicullular structures. Many components involved in chemotaxis to cAMP have been identified in D. discoideum. The binding of cAMP to a GPCR (cAR1) induces dissociation of heterotrimeric G-proteins into G&gamma; and G&beta;&gamma; subunits 7, 9, 10. G&beta;&gamma; subunits activate Ras, which in turn activates PI3K, converting PIP2 into PIP3 on the cell membrane 11-13. PIP3 serve as binding sites for proteins with pleckstrin Homology (PH) domains, thus recruiting these proteins to the membrane 14, 15. Activation of cAR1 receptors also controls the membrane associations of PTEN, which dephosphorylates PIP3 to PIP2 16, 17. The molecular mechanisms are evolutionarily conserved in chemokine GPCR-mediated chemotaxis of human cells such as neutrophils 18. We present following methods for studying chemotaxis of D. discoideum cells. 1. Preparation of chemotactic component cells. 2. Imaging chemotaxis of cells in a cAMP gradient. 3. Monitoring a GPCR induced activation of heterotrimeric G-protein in single live cells. 4. Imaging chemoattractant-triggered dynamic PIP3 responses in single live cells in real time. Our developed imaging methods can be applied to study chemotaxis of human leukocytes.

Imaging G-protein Coupled Receptor GPCR-mediated Signaling Events that Control Chemotaxis of Dictyostelium Discoideum

Here, we describe detailed live cell imaging methods for investigating chemotaxis. We present fluorescence microscopic methods to monitor spatiotemporal dynamics of signaling events in migrating cells. Measurement of signaling events permits us to further understand how a GPCR-signaling network achieves gradient sensing of chemoattractants and controls directional migration of eukaryotic cells.

Many eukaryotic cells can detect gradients of chemical signals in their environments and migrate accordingly 1.  This guided cell migration is referred as ...

Tracking Morphogenetic Tissue Deformations in the Early Chick Embryo

Embryonic epithelia undergo complex deformations (e.g. bending, twisting, folding, and stretching) to form the primitive organs of the early embryo. Tracking fiducial markers on the surfaces of these cellular sheets is a well-established method for estimating morphogenetic quantities such as growth, contraction, and shear. However, not all surface labeling techniques are readily adaptable to conventional imaging modalities and possess different advantages and limitations. Here, we describe two labeling methods and illustrate the utility of each technique. In the first method, hundreds of fluorescent labels are applied simultaneously to the embryo using magnetic iron particles. These labels are then used to quantity 2-D tissue deformations during morphogenesis. In the second method, polystyrene microspheres are used as contrast agents in non-invasive optical coherence tomography (OCT) imaging to track 3-D tissue deformations. These techniques have been successfully implemented in our lab to studythe physical mechanisms of early head fold, heart, and brain development, and should be adaptable to a wide range morphogenetic processes.

This article describes surface labeling and ex ovo tissue culture in the early chick embryo. Techniques amenable to time-lapse bright field, fluorescence, and optical coherence tomography imaging are presented. Tracking surface labels with high spatiotemporal resolution enables kinematic quantities such as morphogenetic strains (deformations) to be calculated in both two and three dimensions.

Embryonic epithelia undergo complex deformations (e.g. bending, twisting, folding, and stretching) to form the primitive organs of the early embryo. ...

Measuring Cation Transport by Na,K- and H,K-ATPase in Xenopus Oocytes by Atomic Absorption Spectrophotometry: An Alternative to Radioisotope Assays

Whereas cation transport by the electrogenic membrane transporter Na+,K+-ATPase can be measured by electrophysiology, the electroneutrally operating gastric H+,K+-ATPase is more difficult to investigate. Many transport assays utilize radioisotopes to achieve a sufficient signal-to-noise ratio, however, the necessary security measures impose severe restrictions regarding human exposure or assay design. Furthermore, ion transport across cell membranes is critically influenced by the membrane potential, which is not straightforwardly controlled in cell culture or in proteoliposome preparations. Here, we make use of the outstanding sensitivity of atomic absorption spectrophotometry (AAS) towards trace amounts of chemical elements to measure Rb+ or Li+ transport by Na+,K+- or gastric H+,K+-ATPase in single cells. Using Xenopus oocytes as expression system, we determine the amount of Rb+ (Li+) transported into the cells by measuring samples of single-oocyte homogenates in an AAS device equipped with a transversely heated graphite atomizer (THGA) furnace, which is loaded from an autosampler. Since the background of unspecific Rb+ uptake into control oocytes or during application of ATPase-specific inhibitors is very small, it is possible to implement complex kinetic assay schemes involving a large number of experimental conditions simultaneously, or to compare the transport capacity and kinetics of site-specifically mutated transporters with high precision. Furthermore, since cation uptake is determined on single cells, the flux experiments can be carried out in combination with two-electrode voltage-clamping (TEVC) to achieve accurate control of the membrane potential and current. This allowed e.g. to quantitatively determine the 3Na+/2K+ transport stoichiometry of the Na+,K+-ATPase and enabled for the first time to investigate the voltage dependence of cation transport by the electroneutrally operating gastric H+,K+-ATPase. In principle, the assay is not limited to K+-transporting membrane proteins, but it may work equally well to address the activity of heavy or transition metal transporters, or uptake of chemical elements by endocytotic processes.

Measuring Cation Transport by Na,K- and H,K-ATPase in Xenopus Oocytes by Atomic Absorption Spectrophotometry: An Alternative to Radioisotope Assays

We describe a method to quantify the activity of K+-countertransporting P-type ATPases by heterologous expression of the enzymes in Xenopus oocytes and measuring Rb+ or Li+ uptake into individual cells by atomic absorption spectrophotometry. The method is a sensitive and safe alternative to radioisotope flux experiments facilitating complex kinetic studies.

Whereas cation transport by the electrogenic membrane transporter Na+,K+-ATPase can be measured by electrophysiology, the electroneutrally operating ...

Live Cell Imaging of Early Autophagy Events: Omegasomes and Beyond

Autophagy is a cellular response triggered by the lack of nutrients, especially the absence of amino acids. Autophagy is defined by the formation of double membrane structures, called autophagosomes, that sequester cytoplasm, long-lived proteins and protein aggregates, defective organelles, and even viruses or bacteria. Autophagosomes eventually fuse with lysosomes leading to bulk degradation of their content, with the produced nutrients being recycled back to the cytoplasm. Therefore, autophagy is crucial for cell homeostasis, and dysregulation of autophagy can lead to disease, most notably neurodegeneration, ageing and cancer.	
	Autophagosome formation is a very elaborate process, for which cells have allocated a specific group of proteins, called the core autophagy machinery. The core autophagy machinery is functionally complemented by additional proteins involved in diverse cellular processes, e.g. in membrane trafficking, in mitochondrial and lysosomal biology. Coordination of these proteins for the formation and degradation of autophagosomes constitutes the highly dynamic and sophisticated response of autophagy. Live cell imaging allows one to follow the molecular contribution of each autophagy-related protein down to the level of a single autophagosome formation event and in real time, therefore this technique offers a high temporal and spatial resolution.	
	Here we use a cell line stably expressing GFP-DFCP1, to establish a spatial and temporal context for our analysis. DFCP1 marks omegasomes, which are precursor structures leading to autophagosomes formation. A protein of interest (POI) can be marked with either a red or cyan fluorescent tag. Different organelles, like the ER, mitochondria and lysosomes, are all involved in different steps of autophagosome formation, and can be marked using a specific tracker dye. Time-lapse microscopy of autophagy in this experimental set up, allows information to be extracted about the fourth dimension, i.e. time. Hence we can follow the contribution of the POI to autophagy in space and time.

Time-lapse microscopy of fluorescently labeled autophagy markers allows monitoring of the dynamic autophagy response with high temporal resolution. Using specific autophagy and organelle markers in a combination of 3 different colors, we can follow the contribution of a protein to autophagosome formation in a robust spatial and temporal context.

Autophagy is a  cellular response triggered by the lack of nutrients, especially the absence of  amino acids. Autophagy is defined by the formation of ...

Analysis of Skeletal Muscle Defects in Larval Zebrafish by Birefringence and Touch-evoke Escape Response Assays

Zebrafish (Danio rerio) have become a particularly effective tool for modeling human diseases affecting skeletal muscle, including muscular dystrophies1-3, congenital myopathies4,5, and disruptions in sarcomeric assembly6,7, due to high genomic and structural conservation with mammals8. Muscular disorganization and locomotive impairment can be quickly assessed in the zebrafish over the first few days post-fertilization. Two assays to help characterize skeletal muscle defects in zebrafish are birefringence (structural) and touch-evoked escape response (behavioral).
Birefringence is a physical property in which light is rotated as it passes through ordered matter, such as the pseudo-crystalline array of muscle sarcomeres9. It is a simple, noninvasive approach to assess muscle integrity in translucent zebrafish larvae early in development. Wild-type zebrafish with highly organized skeletal muscle appear very bright amidst a dark background when visualized between two polarized light filters, whereas muscle mutants have birefringence patterns specific to the primary muscular disorder they model. Zebrafish modeling muscular dystrophies, diseases characterized by myofiber degeneration followed by repeated rounds of regeneration, exhibit degenerative dark patches in skeletal muscle under polarized light. Nondystrophic myopathies are not associated with necrosis or regenerative changes, but result in disorganized myofibers and skeletal muscle weakness. Myopathic zebrafish typically show an overall reduction in birefringence, reflecting the disorganization of sarcomeres.
The touch-evoked escape assay involves observing an embryo&#39;s swimming behavior in response to tactile stimulation10-12. In comparison to wild-type larvae, mutant larvae frequently display a weak escape contraction, followed by slow swimming or other type of impaired motion that fails to propel the larvae more than a short distance12. The advantage of these assays is that disease progression in the same fish type can be monitored in vivo for several days, and that large numbers of fish can be analyzed in a short time relative to higher vertebrates.

The zebrafish is now an established and powerful tool for modeling muscular dystrophies, congenital myopathies, and related neuromuscular diseases. Birefringence and touch-evoked escape behavior are two common noninvasive assays used to determine the degree of muscular disorganization and locomotive impairment of zebrafish embryos during early development.

Zebrafish (Danio rerio) have become a particularly effective tool for modeling human diseases affecting skeletal muscle, including muscular ...

In Vitro Aggregation Assays Using Hyperphosphorylated Tau Protein

Alzheimer's disease is one of a large group of neurodegenerative disorders known as tauopathies that are manifested by the neuronal deposits of hyperphosphorylated tau protein in the form of neurofibrillary tangles (NFTs). The density of NFT correlates well with cognitive impairment and other neurodegenerative symptoms, thus prompting the endeavor of developing tau aggregation-based therapeutics. Thus far, however, tau aggregation assays use recombinant or synthetic tau that is devoid of the pathology-related phosphorylation marks. Here we describe two assays using recombinant, hyperphosphorylated tau as the subject. These assays can be scaled up for high-throughput screens for compounds that can modulate the kinetics or stability of hyperphosphorylated tau aggregates. Novel therapeutics for Alzheimer's disease and other tauopathies can potentially be discovered using hyperphosphorylated tau isoforms.

In Vitro Aggregation Assays Using Hyperphosphorylated Tau Protein

Unmodified and hyperphosphorylated tau proteins were used in two in vitro aggregation assays to reveal the hyperphosphorylation-dependent fast aggregation kinetics. These assays pave the way for future screens for compounds that can modulate the propensity of hyperphosphorylated tau to form fibrils that underlie the progression of Alzheimer&#8217;s disease.

Alzheimer's disease is one of a large group of neurodegenerative disorders known as tauopathies that are manifested by the neuronal deposits of ...

Analysis of Nephron Composition and Function in the Adult Zebrafish Kidney

The zebrafish model has emerged as a relevant system to study kidney development, regeneration and disease. Both the embryonic and adult zebrafish kidneys are composed of functional units known as nephrons, which are highly conserved with other vertebrates, including mammals. Research in zebrafish has recently demonstrated that two distinctive phenomena transpire after adult nephrons incur damage: first, there is robust regeneration within existing nephrons that replaces the destroyed tubule epithelial cells; second, entirely new nephrons are produced from renal progenitors in a process known as neonephrogenesis. In contrast, humans and other mammals seem to have only a limited ability for nephron epithelial regeneration. To date, the mechanisms responsible for these kidney regeneration phenomena remain poorly understood. Since adult zebrafish kidneys undergo both nephron epithelial regeneration and neonephrogenesis, they provide an outstanding experimental paradigm to study these events. Further, there is a wide range of genetic and pharmacological tools available in the zebrafish model that can be used to delineate the cellular and molecular mechanisms that regulate renal regeneration. One essential aspect of such research is the evaluation of nephron structure and function. This protocol describes a set of labeling techniques that can be used to gauge renal composition and test nephron functionality in the adult zebrafish kidney. Thus, these methods are widely applicable to the future phenotypic characterization of adult zebrafish kidney injury paradigms, which include but are not limited to, nephrotoxicant exposure regimes or genetic methods of targeted cell death such as the nitroreductase mediated cell ablation technique. Further, these methods could be used to study genetic perturbations in adult kidney formation and could also be applied to assess renal status during chronic disease modeling.

The zebrafish adult kidney is an excellent system for renal regeneration and disease studies. An essential aspect of such research is the assessment of nephron structure and function. This protocol describes several methodologies that can be implemented to assess nephron tubule composition and to evaluate renal reabsorption.

The zebrafish model has emerged as a relevant system to study kidney development, regeneration and disease. Both the embryonic and adult zebrafish kidneys ...