Name: techniques for imaging prometaphase and metaphase of meiosis i in fixed drosophila oocytes
Uploaded: 2016-10-31T15:00:00
Description: Watch this Scientific Journal Video about Techniques for Imaging Prometaphase and Metaphase of Meiosis I in Fixed Drosophila Oocytes at JoVE.com

We thank Christian Lehner for providing the CENP-C antibody and Eric Joyce for recommendations on FISH. Work in the McKim lab was funded by a grant from NIH (GM101955).

Note: Procedures are performed at room temperature unless otherwise noted. Temperature-controlled incubators are used to maintain temperatures for fly rearing and crosses unless otherwise noted.
1. Preparations
<ol>
	<li>Prepare Flies.
	<ol>
		<li>Prometaphase-enriched oocyte collections.
		<ol>
			<li>Clear adult flies from healthy, young stock or cross cultures. Age bottles for two days at 25 &#176;C. 
			&#8203;NOTE: Generally two healthy bottles will suffice, although more may be needed for some cross c...

<ol>
	<li>Bridges, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-disjunction+as+proof+of+the+chromosome+theory+of+heredity.">Non-disjunction as proof of the chromosome theory of heredity.</a> Genetics. 1 (1), 1-52 (1916).</li><li>Hassold, T., Hunt, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=To+err+(meiotically)+is+human:+the+genesis+of+human+aneuploidy.">To err (meiotically) is human: the genesis of human aneuploidy.</a> Nat Rev Genet. 2 (4), 280-291 (2001).</li><li>Theurkauf, W. E., Hawley, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Meiotic+spindle+assembly+in+Drosophila+females:+behavior+of+nonexchange+chromosomes+and+the+effects+of+mutations+in+the+nod+kinesin-like+protein.">Meiotic spindle assembly in Drosophila females: behavior of nonexchange chromosomes and the effects of mutations in the nod kinesin-like protein.</a> J Cell Biol. 116 (5), 1167-1180 (1992).</li><li>Zou, J., Hallen, M. A., Yankel, C. D., Endow, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+microtubule-destabilizing+kinesin+motor+regulates+spindle+length+and+anchoring+in+oocytes.">A microtubule-destabilizing kinesin motor regulates spindle length and anchoring in oocytes.</a> J Cell Biol. 180 (3), 459-466 (2008).</li><li>Dernburg, A. F., Sedat, J. W., Hawley, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+evidence+of+a+role+for+heterochromatin+in+meiotic+chromosome+segregation.">Direct evidence of a role for heterochromatin in meiotic chromosome segregation.</a> Cell. 86 (1), 135-146 (1996).</li><li>Gilliland, W. D., Hughes, S. F., Vietti, D. R., Hawley, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Congression+of+achiasmate+chromosomes+to+the+metaphase+plate+in+Drosophila+melanogaster+oocytes.">Congression of achiasmate chromosomes to the metaphase plate in Drosophila melanogaster oocytes.</a> Dev Biol. 325 (1), 122-128 (2009).</li><li>Gilliland, W. 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=Hypoxia+transiently+sequesters+mps1+and+polo+to+collagenase-sensitive+filaments+in+Drosophila+prometaphase+oocytes.">Hypoxia transiently sequesters mps1 and polo to collagenase-sensitive filaments in Drosophila prometaphase oocytes.</a> PLoS One. 4 (10), e7544 (2009).</li><li>Sullivan, W., Ashburner, M., Hawley, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Drosophila Protocols. , (2000).</li><li>Radford, S. J., Hoang, T. L., G&#322;uszek, A. A., Ohkura, H., McKim, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lateral+and+End-On+Kinetochore+Attachments+Are+Coordinated+to+Achieve+Bi-orientation+in+Drosophila+Oocytes.">Lateral and End-On Kinetochore Attachments Are Coordinated to Achieve Bi-orientation in Drosophila Oocytes.</a> PLoS Genet. 11 (10), e1005605 (2015).</li><li>Smurnyy, Y., Toms, A. V., Hickson, G. R., Eck, M. J., Eggert, U. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Binucleine+2,+an+isoform-specific+inhibitor+of+Drosophila+Aurora+B+kinase,+provides+insights+into+the+mechanism+of+cytokinesis.">Binucleine 2, an isoform-specific inhibitor of Drosophila Aurora B kinase, provides insights into the mechanism of cytokinesis.</a> ACS Chem Biol. 5 (11), 1015-1020 (2010).</li><li>Mahowald, A. P., Goralski, T. J., Caulton, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+activation+of+Drosophila+eggs.">In vitro activation of Drosophila eggs.</a> Dev Biol. 98 (2), 437-445 (1983).</li><li>Page, A. W., Orr-Weaver, T. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+the+meiotic+divisions+in+Drosophila+oocytes.">Activation of the meiotic divisions in Drosophila oocytes.</a> Dev Biol. 183 (2), 195-207 (1997).</li><li>Tavosanis, G., Llamazares, S., Goulielmos, G., Gonzalez, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Essential+role+for+gamma-tubulin+in+the+acentriolar+female+meiotic+spindle+of+Drosophila.">Essential role for gamma-tubulin in the acentriolar female meiotic spindle of Drosophila.</a> EMBO J. 16 (8), 1809-1819 (1997).</li><li>Endow, S. A., Komma, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spindle+dynamics+during+meiosis+in+Drosophila+oocytes.">Spindle dynamics during meiosis in Drosophila oocytes.</a> J Cell Biol. 137 (6), 1321-1336 (1997).</li><li>Matthies, H. J., Clarkson, M., Saint, R. B., Namba, R., Hawley, R. S., Sullivan, W., Ashburner, M., Hawley, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Drosophila Protocols. , 67-85 (2000).</li><li>Colombi&#233;, N., 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=Dual+roles+of+Incenp+crucial+to+the+assembly+of+the+acentrosomal+metaphase+spindle+in+female+meiosis.">Dual roles of Incenp crucial to the assembly of the acentrosomal metaphase spindle in female meiosis.</a> Development. 135 (19), 3239-3246 (2008).</li></ol>

Staging Drosophila Oocytes
Although an elongated karyosome is often seen in prometaphase oocytes, using karyosome shape to distinguish prometaphase from metaphase oocytes can be problematic. During prometaphase, the karyosome begins as a round shape, elongates, and then retracts to a round shape as the oocyte approaches the metaphase arrest. This means that many prometaphase oocytes do not have an elongated karyosome. In addition, if mutant or drug-treated oocytes are...

The study of meiosis is sometimes described as the "genetics of genetics". This is because the fundamental properties of chromosome inheritance and independent assortment are carried out through the segregation of chromosomes during gamete production. An important demonstration of the chromosome theory of inheritance came in 1916 from the work of Calvin Bridges in Drosophila melanogaster1. This and other classical genetics studies in Drosophila contributed greatly to our understanding of genetics. Cytological examination of meiotic chromosomes in Drosophila oocytes, however, has been challenging. This is primarily because immunofluorescence of late-stage Drosophila oocytes, when the spindle assembles and chromosomes are oriented for segregation, is hampered by the presence of membranes that render the oocyte impenetrable to antibodies.
Despite this challenge, Drosophila oocytes remain an attractive model for the study of chromosome behavior and spindle assembly. This is because of the powerful genetic tools available in Drosophila, but also because the oocytes arrest at metaphase I, when the chromosomes are oriented and the spindle is fully formed. This facilitates the collection and examination of large numbers of oocytes at this important stage of cell division. In addition, a simple model organism that is amenable to genetic manipulation for the study of oocyte chromosome segregation can provide an important contribution to our understanding of human reproductive health. Errors in chromosome number are the leading genetic cause of miscarriage and birth defects in humans2. A majority of these errors can be traced to the oocyte and are correlated with increasing maternal age. The average age of mothers in the U.S. has been increasing, making this a major public health concern.
We describe here methods for the cytological examination of Drosophila oocytes, including a demonstration of how to remove the oocyte membranes. These methods are modifications of protocols first described by Theurkauf and Hawley3, Zou et al.4, and Dernburg et al.5. We also include methods for the enrichment of different stages of oocytes, based on a protocol first described by Gilliland et al.6. Finally, we add instructions for the drug treatment of Drosophila oocytes. Together, these methods allow the cytological investigation of oocyte chromosome segregation and spindle assembly in Drosophila.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>15 mL conical tubes</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>16% formaldehyde</td>
			<td>Ted Pella, Inc.</td>
			<td>18505</td>
			<td>HAZARDOUS; once opened, discard after one month</td>
		</tr>
		<tr>
			<td>250 mL beakers</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>5 mL tubes</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>active dry yeast</td>
			<td>Various</td>
			<td></td>
			<td>mix with water to make a paste the consistency of peanut butter</td>
		</tr>
		<tr>
			<td>anti-&#945;-tubulin antibody conjugated to FITC</td>
			<td>Sigma</td>
			<td>F2168</td>
			<td>clone DM1A</td>
		</tr>
		<tr>
			<td>Binucleine 2</td>
			<td>Sigma</td>
			<td>B1186</td>
			<td>HAZARDOUS</td>
		</tr>
		<tr>
			<td>blender</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>bovine serum albumin</td>
			<td>Sigma</td>
			<td>A4161</td>
			<td></td>
		</tr>
		<tr>
			<td>calcium chloride</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>colchicine</td>
			<td>Sigma</td>
			<td>C-9754</td>
			<td>HAZARDOUS</td>
		</tr>
		<tr>
			<td>coverslips</td>
			<td>VWR</td>
			<td>48366-227</td>
			<td>No. 1 1/2</td>
		</tr>
		<tr>
			<td>dextran sulfate</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DMSO</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>EGTA</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ethanol</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>forceps</td>
			<td>Ted Pella, Inc.</td>
			<td>5622</td>
			<td>Dumont tweezers high precision grade style 5</td>
		</tr>
		<tr>
			<td>formamide</td>
			<td>Sigma</td>
			<td>47670-250ML-F</td>
			<td></td>
		</tr>
		<tr>
			<td>glass slides</td>
			<td>VWR</td>
			<td>48312-003</td>
			<td></td>
		</tr>
		<tr>
			<td>glucose</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>graduated 1.5 mL tubes</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>VWR</td>
			<td>EM-5330</td>
			<td>available from several venders</td>
		</tr>
		<tr>
			<td>Hoechst 33342</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>magnesium chloride</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>methanol</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>large mesh (~1500 &#181;m)</td>
			<td>VWR</td>
			<td>AA43657-NK</td>
			<td>variety of formats and other suppliers, 12 or 14 mesh</td>
		</tr>
		<tr>
			<td>small mesh (~300 &#181;m)</td>
			<td>Spectrum labs</td>
			<td>146 424</td>
			<td>variety of formats, eg 146 422 or 146 486</td>
		</tr>
		<tr>
			<td>nutator</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Pasteur pipets</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>potassium acetate</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cacodylic acid</td>
			<td>Sigma</td>
			<td>C0125</td>
			<td>HAZARDOUS; alternatively, sodium cacodylate may be substituted</td>
		</tr>
		<tr>
			<td>potassium hydroxide</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>sodium acetate</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>sodium chloride</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>sodium citrate</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>sodium hydroxide</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>sucrose</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>taxol (paclitaxel)</td>
			<td>Sigma</td>
			<td>T1912</td>
			<td>HAZARDOUS</td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Fisher</td>
			<td>PI-28314</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween 20</td>
			<td>Fisher</td>
			<td>PI-28320</td>
			<td></td>
		</tr>
		<tr>
			<td>vortex</td>
			<td>Various</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

techniques for imaging prometaphase and metaphase of meiosis i in fixed drosophila oocytes

Chromosome segregation in human oocytes is error prone, resulting in aneuploidy, which is the leading genetic cause of miscarriage and birth defects. The study of chromosome behavior in oocytes from model organisms holds much promise to uncover the molecular basis of the susceptibility of human oocytes to aneuploidy. Drosophila melanogaster is amenable to genetic manipulation, with over 100 years of research, community, and technique development. Visualizing chromosome behavior and spindle assembly in Drosophila oocytes has particular challenges, however, due primarily to the presence of membranes surrounding the oocyte that are impenetrable to antibodies. We describe here protocols for the collection, preparation, and imaging of meiosis I spindle assembly and chromosome behavior in Drosophila oocytes, which allow the molecular dissection of chromosome segregation in this important model organism.

The methods we have described here will result in the collection of late-stage Drosophila oocytes representing three stages of meiosis (Figure 1). Oocytes in prophase are distinguished by the presence of the nuclear envelope, which is visible by the lack of tubulin signal in the region surrounding the karyosome (Figure 1A). Prometaphase is the period after nuclear envelope breakdown during which the spindle assembles. During prometaphase, the kar...

Watch this Scientific Journal Video about Techniques for Imaging Prometaphase and Metaphase of Meiosis I in Fixed Drosophila Oocytes at JoVE.com

Techniques for Imaging Prometaphase and Metaphase of Meiosis I in Fixed Drosophila Oocytes

We present protocols for the collection, preparation, and imaging of mature Drosophila oocytes. These methods allow the visualization of chromosome behavior and spindle assembly and function during meiosis.

Techniques for Imaging Prometaphase and Metaphase of Meiosis I in Fixed Drosophila Oocytes

Chromosome segregation in human oocytes is error prone, resulting in aneuploidy, which is the leading genetic cause of miscarriage and birth defects. The ...

The overall goal of this procedure is to prepare Drosophila oocytes for the cytological examination of spindle assembly and chromosome orientation during meiosis I.This method can help answer key questions in the meiosis field, such as how spindle bipolarity is established and how chromosomes become bi-oriented in the absence of centrosomes. The main advantage of this technique is that the oocyte membranes that block antibody penetration are effectively removed, which allows immunofluorescence. To begin pre-coat the inside of a five-millimeter tube and pasture pipette with PTB to prevent oocytes sticking to the surfaces.Add 100 milliliters of ROB's buffer to a blender and then add 100 to 300 anesthetized flies and pulse three times for one second. Filter the resulted slurry into a 250-milliliter beaker through a large mesh with pores of around 1, 500 micrometers. Let the filtrate settle for around two minutes and then aspirate the top layer, removing as many large body parts as possible.Filter the slurry again into a 250-milliliter beaker, through a smaller mesh with the pore size of 300 micrometers. Rinse the first beaker using additional buffer in the coated pipette to collect the remaining oocytes. Let the slurry settle for three minutes and then aspirate all but the bottom 10 milliliters.Pour as much of the 10 milliliters as possible into the coated five-milliliter tube. Let the slurry settle for around two minutes and then carefully remove the liquid. Add the remainder of the 10 milliliters of slurry and let the mix settle again before removing the liquid.Rinse any remaining oocytes out of the beaker using additional buffer in the coated pipette. Let the rinse settle in the five-milliliter tube for three to five minutes. To fix the ovaries, first aspirate off all liquid from the tissues and immediately add one milliliter of Fix Mix.Place the tissues on a nutator for 2 1/2 minutes. Next, add one milliliter of heptane, vortex the tube for one minute, and then allow the oocytes to settle for a further minute. Remove all liquid from the settled tissue, then add one milliliter of 1x PBS.Vortex the tube for 30 seconds and then allow the oocytes to settle for one minute. After that, remove all liquid from the tube and fill it with five milliliters of 1x PBS. Using the coated pipette, add roughly 500 to 1, 000 oocytes to a frosted glass slide.Remove any extraneous body parts or material using forceps. Place a cover slip on top of the tissue and gently roll the oocytes until all membranes are removed. Dragging the edge of the coverslip across the oocytes works well.Check the progress of membrane removal under a microscope periodically. Too much pressure will destroy the oocytes. The most effective oocyte membrane removal is achieved by combining the maximum amount of oocyte movement with the minimum amount of pressure.Use a light touch and quick movements to drag the edge of the coverslip across the oocytes. To begin extraction and blocking, add 15 milliliters of PBS 1%Triton X-100 to a 50-milliliter tube. Rinse the rolled oocytes into this tube and nutate for 1 1/2 to two hours.After allowing the oocytes to settle for two minutes, remove the liquid along with as many membranes as possible and add 50 milliliters of PBS 0.05%Triton X-100. Let the oocytes settle for a further two minutes, and then remove all but around one milliliter of liquid. Transfer the oocytes to a graduated 1.5 milliliter tube and remove the remaining liquid.Add one milliliter of PTB for blocking and nutate for one hour. Remove the liquid from the oocytes and then add 300 microliters of PTB. Next, add the primary antibody of interest at the appropriate dilution, taking care to protect the samples treated with fluorescent antibody from light.Nutute overnight at four degrees Celsius. Wash the oocytes and one milliliter of PTB four times for 15 minutes each. Remove the liquid, and add 200 microliters of supernatant from the secondary antibody-treated embryos.Filter the 300-microliter mark with PTB and then nutate for three to four hours at room temperature. Wash the oocytes once for 15 minutes with one milliliter of PTB. Next, remove the liquid and add 0.5 microliters of Hoechst 33342 and 500 microliters of PTB.Set to nutate for seven minutes. Use one milliliter of PTB to wash the oocytes two times for 15 minutes each. The samples can now be mounted and imaged immediately using standard confocal microscopy techniques, or stored in PTB at four degrees Celsius until needed.Images of late-stage oocytes generated using the demonstrated technique are shown here, capturing three different stages of meiosis. Oocytes in prophase are distinguished by the presence of the nuclear envelope which is visible due to the lack of tubulin signal in the regions surrounding the karyosome. The distinctive elongation of the karyosome in the prometaphase was also observed, and the fourth chromosomes are seen apart from the karyosome mass.Metaphase was also captured and the karyosome is seen retracted into a round shape. Here immunostaining with different antibodies highlights the spindle, centromeres, and central spindle in oocytes fixed with formaldehyde and heptane. Oocytes treated with the drug Colchicine showed non-standard phenotypes with the elimination of most non-kinetic or microtubules, resulting in all microtubules contacting the DNA at centromere labeled Phocyde.Treatment with Paclitaxel resulted in oocytes with excessive microtubules in the cytoplasm. Finally oocytes treated with Binucleine 2 to inhibit Aurora B kinase, showed complete loss of spindle microtubules. While attempting this procedure, it's important to remember not to rush during oocyte membrane removal, because the success of the protocol depends on this step.Generally individuals new to this method will struggle, because the removal of the membranes requires patience and practice. This technique is therefore best learned by watching someone perform it successfully. Once mastered, rolling the oocytes can be done in five to 10 minutes.But it's possible to take up to 30 minutes without affecting the quality of the results. After watching this video, you should have a good understanding of how to prepare late-stage Drosophila oocytes for imaging biotic spindle assembly, spindle organization, chromosome movements, and chromosome bi-orientation. Thanks for watching, and good luck with your experiments.

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Unit 2

Meiosis

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The  proper elimination of unwanted or aberrant cells through apoptosis and  subsequent phagocytosis (apoptotic cell clearance) is crucial for normal  ...

Organelle Transport in Cultured Drosophila Cells: S2 Cell Line and Primary Neurons.

Organelle Transport in Cultured Drosophila Cells: S2 Cell Line and Primary Neurons.

Drosophila S2 cells plated on a coverslip in the presence of any actin-depolymerizing drug form long unbranched processes filled with uniformly polarized ...