The authors acknowledge the technical assistance of Abigail Harris. They also acknowledge Paula Cohen and Kim Holloway for helping to optimize the protocol of preparing surface-spread nuclei from mouse spermatocytes. The authors also appreciate critical reading of the manuscript by Karen Schindler.
This work was supported by NIH R01 GM106262 to K.M.B.

All methods involving mice utilized high ethical and welfare standards, and were approved by the Institutional Animal Care and Use Committee at Drexel University College of Medicine.
1. Preparation of solutions and instruments needed
<ol>
	<li>Prepare Hypotonic Extraction Buffer (HEB) in 50 mL of ultrapure laboratory grade water, pH 8.2 - 8.4 (Table 1). Make the solution fresh each time, keep on ice, and use within 2 h of preparing spreads; this is necessary to optimize the reducing and protease inhibiting activities of DTT and PMSF, respectively. Use 10 mL of HEB for each pair of mouse testes.</li>
	<li>Prepare a 100 mM sucrose solution (fresh each time) by adding 0.342 g of sucrose to 10 mL of ultrapure laboratory grade water. Adjust the pH to 8.2</li>
	<li>Prepare fixative solution (1% paraformaldehyde (PFA), 0.15% Triton X-100, pH adjusted to 9.2 with 1 N HCl or 1 N NaOH) fresh monthly and store it at room temperature protected from light. Dilute a 16% commercially available PFA starting stock to 4% in 1X PBS for use as a working stock, and then store 4% aliquots at -20 &#176;C.
	<ol>
		<li>To prepare the fixative solution, add 10 mL of 4% PFA solution and 600 &#181;L of 10% Triton X-100 to 30 mL of 1X PBS, mix well, and adjust the pH to 9.2 with 1 N HCl or 1 N NaOH. Store the fixative solution in a 50-mL conical tube wrapped in aluminum foil at room temperature (for no more than 4 weeks).</li>
	</ol>
	</li>
	<li>Prepare wash solutions (while slides are drying the last 30 min) with Photo-Flo 200: 0.4% Photo-Flo 200/PBS (320 &#181;L of Photo-Flo 200 in 80 mL of 1X PBS) and 0.4% Photo-Flo 200/dH2O (160 &#181;L of Photo-Flo 200 in 40 mL of ultrapure laboratory grade water). Use a 50 mL Coplin jar filled with 40 mL of solutions to wash 10 or fewer slides at a time.</li>
	<li>Prepare the following instruments: 1 pair of surgical scissors (to incise the skin), 1 pair of fine tip surgical scissors (to incise the peritoneum), 2 pairs of straight fine tip forceps (to dissect out each testis), 1 straight edge razor blade (to incise each testis), 2 pairs of curved tip forceps (to immobilize each testis and squeeze out the seminiferous tubules), 50 mL Coplin jars, Teflon printed 3 ring slides, 1 scalpel with size 11 blade, humidified chamber, 100 x 15 mm Petri dishes, fine tip permanent marker or pencil, and a platform rotating shaker.
	<ol>
		<li>Place premium uncharged precleaned frosted end glass slides upright in a 50 mL Coplin jar filled with fixative solution until use. 
		NOTE: Pencil is preferred if slides will be used subsequently in procedures requiring ethanol, such as fluorescence in situ hybridization.</li>
	</ol>
	</li>
</ol>
2. Spermatocyte nuclei spreading
<ol>
	<li>Euthanize a male mouse according to institutional guidelines (e.g. cervical dislocation with or without CO2 asphyxiation).</li>
	<li>Use P10 - P20 males to evaluate meiotic cells in the first wave of spermatogenesis; we routinely use P15 - P17 males to obtain cells from all substages of prophase I. Adult testes will provide cells from prophase I too, but they will also yield more postmeiotic cells, such as spermatids.</li>
	<li>Harvest and weigh the testes (record the paired weights); then place them into a Petri dish containing a few drops of cold HEB to keep them moist.</li>
	<li>Hold the testis against the bottom of the dish with curved tip forceps and use a straight edge razor blade to make a small vertical midline incision through the capsule of the testis. While still holding the testis against the bottom of the dish with one forceps, use a second set of curved tip forceps or straight edge razor blade to gently squeeze the seminiferous tubules from the testis.
	<ol>
		<li>Place the tubules into a 15 mL conical tube containing 10 mL of cold HEB, taking care to avoid putting pieces of capsule into the tube. Repeat these steps with the second testis.</li>
	</ol>
	</li>
	<li>Incubate the decapsulated seminiferous tubules in the conical tube containing HEB on ice for 30 - 60 min, depending on the size of the testes. Incubate seminiferous tubules from a pair of testes weighing 30 mg or less for 30 min, tubules from a pair of testes weighing 31 to 50 mg for 30 - 45 minutes, and larger testes for 60 minutes. Do not alter the times for a single testis. 
	NOTE: The optimal incubation time may vary depending on the experience of the experimenter, the reagents used, and the mice being analyzed.</li>
	<li>While seminiferous tubules are incubating in HEB, use a marker or pencil to label the frosted ends of precleaned slides with mouse number, slide number, and date. Then place the pre-cleaned slides in a Coplin jar containing the fixative solution.</li>
	<li>Following incubation, pour tubules and HEB into a clean Petri dish, and separate tubules into approximately 3 mm diameter clumps. Each clump yields 2 slides and the number of slides yielded depends on the size of testes. 
	NOTE: We obtain 8 slides from wild type and 6 slides from subfertile Chtf18-null P16 testes (which are smaller due to decreased numbers of meiotic and mitotic germ cells8). One adult testis weighing 100 mg or more would be expected to yield 16 slides.</li>
	<li>Place 23 &#181;L of 100 mM sucrose solution into one ring of a Teflon printed, 3 ring slide and add one clump of seminiferous tubules to the ring.&#160; Then using curved tip forceps to hold the clump, gently mince the tubules with a size 11 razor blade until the solution becomes cloudy. 
	NOTE: Do not overmince as this will result in fragmented chromosomes. Note that fragmented chromosomes could also be indicative of a mutant phenotype.</li>
	<li>Remove debris, add another 23 &#181;L of sucrose solution, and use a micropipette to gently pipette the mixture up and down a few times to help separate the cells in the suspension.</li>
	<li>Remove a slide soaking in the Coplin jar containing fixative solution and tilt the slide over the jar so that one generous droplet collects at the bottom corner of the slide.
	<ol>
		<li>Pipet 20 &#181;L of sucrose cell suspension from the ring of the Teflon printed 3 ring slide into the fixative droplet on a premium frosted glass slide, and pipet the suspension up and down 2 - 3 times. 
		NOTE: The fixative droplet should be large enough in volume so that addition of 20 &#956;L of the sucrose cell suspension to it allows coverage across the entire slide when the mixture is spread (see 2.11 below).</li>
	</ol>
	</li>
	<li>Slowly tilt the slide to the side opposite the droplet to spread the cell suspension along the length of the slide. Then slowly tilt the slide back to spread the cell suspension along the width of the slide to cover it completely. Avoid spreading the suspension over the same area of the slide more than once otherwise the cells will overlap with each other.</li>
	<li>Immediately place slide flat in a humidified chamber and repeat steps 2.8 to 2.11 until all clumps of seminiferous tubules have been used to make slides. It is important not to move the humidified chamber during the drying process to avoid tearing and overlapping cells.</li>
	<li>Allow the slides to incubate in a covered humidified chamber at room temperature for 2.5 h so that they dry slowly and not completely. High humidity and slow drying in this step are important to ensure adequate spreading of the chromatin. Then remove the cover of the chamber and allow slides to air-dry completely an additional 30 min.</li>
	<li>Place slides (back to back or in a zigzag pattern) in a Coplin jar containing 0.4% Photo-Flo 200/1X PBS solution and wash the slides twice, 5 min each, by gently agitating the Coplin jar on a platform rotating shaker. Use fresh solution for each wash and keep slides from different mice in separate jars for each of the washes.</li>
	<li>Wash the slides in a Coplin jar containing 0.4% Photo-Flo 200/dH2O solution for 5 min once while agitating.</li>
	<li>Remove slides from the Coplin jar (last wash), carefully wipe the edges and bottoms of the slides to remove excess liquid, and place slides at an angled, almost-upright position to dry. An experimenter who is proficient in this technique can process and prepare surface-spread nuclei from 4 or 5 mice in one day.</li>
	<li>Once dry (15 - 20 min), process slides immediately for immunofluorescence staining or store at -80 &#176;C in a tightly closed slide box protected from light for a maximum of 3 weeks (depending on the target proteins being evaluated; optimal results may be obtained if stained the same day or within 2 weeks).
	<ol>
		<li>If stored at -80 &#176;C, then allow slides to come to room temperature and wash in a Coplin jar containing 1X PBS or Block for 5 min prior to staining. 
		NOTE: Many different immunofluorescence staining protocols will provide good results; refer to Berkowitz et al. for an immunostaining protocol8.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Handel, M. A., Schimenti, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetics+of+mammalian+meiosis:+regulation,+dynamics+and+impact+on+fertility.">Genetics of mammalian meiosis: regulation, dynamics and impact on fertility.</a> Nat Rev Genet. 11, 124-136 (2010).</li><li>Peters, A. H., Plug, A. W., van Vugt, M. J., de Boer, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+drying-down+technique+for+the+spreading+of+mammalian+meiocytes+from+the+male+and+female+germline.">A drying-down technique for the spreading of mammalian meiocytes from the male and female germline.</a> Chromosome Res. 5, 66-68 (1997).</li><li>Counce, S. J., Meyer, G. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differentiation+of+the+synaptonemal+complex+and+the+kinetochore+in+Locusta+spermatocytes+studied+by+whole+mount+electron+microscopy.">Differentiation of the synaptonemal complex and the kinetochore in Locusta spermatocytes studied by whole mount electron microscopy.</a> Chromosoma. 44, 231-253 (1973).</li><li>Speed, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Meiosis+in+the+foetal+mouse+ovary.+I.+An+analysis+at+the+light+microscope+level+using+surface-spreading.">Meiosis in the foetal mouse ovary. I. An analysis at the light microscope level using surface-spreading.</a> Chromosoma. 85, 427-437 (1982).</li><li>Ashley, T., 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=Dynamic+changes+in+Rad51+distribution+on+chromatin+during+meiosis+in+male+and+female+vertebrates.">Dynamic changes in Rad51 distribution on chromatin during meiosis in male and female vertebrates.</a> Chromosoma. 104, 19-28 (1995).</li><li>Baker, S. 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=Involvement+of+mouse+mLh1+in+DNA+mismatch+repair+and+meiotic+crossing+over.">Involvement of mouse mLh1 in DNA mismatch repair and meiotic crossing over.</a> Nat Genet. 13, 336-342 (1996).</li><li>Plug, A. W., Xu, J., Reddy, G., Golub, E. I., Ashley, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Presynaptic+association+of+Rad51+protein+with+selected+sites+in+meiotic+chromatin.">Presynaptic association of Rad51 protein with selected sites in meiotic chromatin.</a> Proc Natl Acad Sci U S A. 93, 5920-5924 (1996).</li><li>Berkowitz, K. 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=Disruption+of+CHTF18+causes+defective+meiotic+recombination+in+male+mice.">Disruption of CHTF18 causes defective meiotic recombination in male mice.</a> PLoS Genet. 8, e1002996 (2012).</li><li>Gomez, 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=Sororin+loads+to+the+synaptonemal+complex+central+region+independently+of+meiotic+cohesin+complexes.">Sororin loads to the synaptonemal complex central region independently of meiotic cohesin complexes.</a> EMBO Rep. 17, 695-707 (2016).</li><li>Brooker, A. S., Berkowitz, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+roles+of+cohesins+in+mitosis,+meiosis,+and+human+health+and+disease.">The roles of cohesins in mitosis, meiosis, and human health and disease.</a> Methods Mol Biol. 1170, 229-266 (2014).</li><li>McNicoll, F., Stevense, M., Jessberger, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cohesin+in+gametogenesis.">Cohesin in gametogenesis.</a> Curr Top Dev Biol. 102, 1-34 (2013).</li><li>Rankin, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Complex+elaboration:+making+sense+of+meiotic+cohesin+dynamics.">Complex elaboration: making sense of meiotic cohesin dynamics.</a> FEBS J. 282, 2426-2443 (2015).</li><li>Holloway, J. K., Sun, X., Yokoo, R., Villeneuve, A. M., Cohen, P. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mammalian+CNTD1+is+critical+for+meiotic+crossover+maturation+and+deselection+of+excess+precrossover+sites.">Mammalian CNTD1 is critical for meiotic crossover maturation and deselection of excess precrossover sites.</a> J Cell Biol. 205, 633-641 (2014).</li><li>La Salle, S., Sun, F., Handel, 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=Isolation+and+short-term+culture+of+mouse+spermatocytes+for+analysis+of+meiosis.">Isolation and short-term culture of mouse spermatocytes for analysis of meiosis.</a> Methods Mol Biol. 558, 279-297 (2009).</li><li>Wiltshire, T., Park, C., Caldwell, K. A., Handel, 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=Induced+premature+G2/M-phase+transition+in+pachytene+spermatocytes+includes+events+unique+to+meiosis.">Induced premature G2/M-phase transition in pachytene spermatocytes includes events unique to meiosis.</a> Dev Biol. 169, 557-567 (1995).</li></ol>

The authors have nothing to disclose.

To obtain high numbers of well spread, good quality spermatocyte nuclei, the most critical steps of this protocol include appropriate incubation time of seminiferous tubules in HEB, appropriate mincing of seminiferous tubules, and the technique employed to spread the sucrose cell suspension across the fixative coated slide(s). We incubate seminiferous tubules from testes of wild type males ranging from postnatal day 15 to adulthood in HEB for 45 min, while testes from comparably aged Chtf18-null mice are incubat...

Mice are used extensively as a model organism to study meiosis in mammals. Both the normal developmental processes and defects that occur during meiosis can be evaluated. The timeline and progression of salient features that occur during prophase I and substages, as well as a multitude of specific proteins involved in processes crucial to regulation of meiosis can be characterized in both wild type and mutant mice. Several specialized processes that occur during meiosis I can be studied in detail (reviewed in Handel and Schimenti1). These include DNA double-strand break (DSB) formation and repair, recombination, synaptonemal complex formation, and chromosome segregation.
An important aspect of studying meiotic processes is the ability to examine nuclei containing homologous chromosomes that are visually and optically resolved to better distinguish and identify the substages of prophase I. Prophase I is comprised of 5 substages that are characterized by specific features including formation of the synaptonemal complex (SC). The SC is a tripartite protein scaffold that enables pairing and DNA double-strand break repair of homologs. During leptonema, homologs align as axial elements of the SC are laid down. Then attachment of central elements to the synaptonemal complex during zygonema facilitates pairing and physical connection (synapsis) between pairs of homologs. During pachynema, synapsis of homologs becomes complete and DNA crossovers are formed from repair of a select population of DNA double-strand breaks via homologous recombination. The SC disassembles during diplonema, allowing homologs to desynapse but remain attached at their centromeres and at sites of DNA crossovers. Finally during diakinesis, homologs recondense and the transition to metaphase occurs1.
Historically, surface-spreading of meiotic chromatin yielded few nuclei, especially those from early stages of prophase I2. As a result, these methods were modified to improve the separation of cells from tissues (i.e. testis or ovary), the technique of spreading meiotic chromatin, and the yield of high quality meiotic nuclei for evaluation2,3,4. In addition, this method proved to be useful in preserving nuclear and chromatin bound proteins in meiotic nuclei as demonstrated by published immunolocalization techniques5,6,7. Therefore, the method initially described by Peters2 and demonstrated here yields many separate burst spermatocyte nuclei containing homologs undergoing the leptotene, zygotene, pachytene, diplotene, and diakinesis substages of prophase I.
The technique of preparing surface-spread nuclei (also called chromatin spread analysis) is widely used to study meiosis in the fields of reproductive and cell biology. Slides containing surface-spread nuclei can be subsequently immunostained with antibodies to proteins of interest or subjected to silver staining, and then analyzed with microscopy. The method is similar for both male and female mice, although modifications have been described for female mice2. It is crucial not to overmince seminiferous tubules. Nuclei must also be well spread so that following immunostaining homologs and associated proteins are clearly seen with microscopy. Surface-spread nuclei can be prepared in just a few hours and either immunostained immediately or stored at -80 &#176;C for a maximum of 3 weeks before thawing and immunostaining. However, optimal results are best obtained for some proteins if immunostaining is performed immediately or within 2 weeks of preparing surface-spread nuclei. Slides can be immunostained with a standard protocol using antibodies to proteins of interest, followed by incubation with secondary antibodies conjugated to fluorescent proteins or dyes, then imaged with fluorescence microscopy8. At postnatal day 15 - 21 there is sufficient tissue per pair of wild type testes to yield 6 - 10 slides, and older mice (including adults) will yield more slides. However, wild type mice 6 weeks of age and older will also yield more post-meiotic cells (i.e. spermatids) on the slides following immunostaining. In addition, all substages of prophase I can be observed in juvenile and adult mice. Testes from males at postnatal days 10 through 15 will yield many more leptotene and zygotene cells. Mice older than postnatal day 14 to 15 will yield more pachytene and diplotene nuclei.
Here we describe and demonstrate a widely-used method of preparing surface-spread nuclei from mouse spermatocytes.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Photo-Flo 200</td>
			<td>Kodak</td>
			<td>1464510</td>
			<td></td>
		</tr>
		<tr>
			<td>16% Paraformaldehyde (formaldehyde aqueous solution)</td>
			<td>Electron Microscopy Sciences</td>
			<td>RT 15710</td>
			<td>Dilute 16% solution into 4% working stocks with 1X PBS and freeze aliquots at -20 &#176;C</td>
		</tr>
		<tr>
			<td>Teflon printed 3 ring slides</td>
			<td>Electron Microscopy Sciences</td>
			<td>63418-11</td>
			<td></td>
		</tr>
		<tr>
			<td>Premium uncharged frosted end glass slides</td>
			<td>Several commercial brands</td>
			<td></td>
			<td>Clean slides in ethyl or isopropyl alcohol and allow to drip dry prior to use; label slides on frosted end with a permanent marker or pencil depending on subsequent use of slides</td>
		</tr>
		<tr>
			<td>Surgical scissors (sharp and blunt tips)</td>
			<td>Fine Science Tools</td>
			<td>14001-12</td>
			<td>Different brand of a similar type will work</td>
		</tr>
		<tr>
			<td>Fine tip surgical scissors (sharp tips)</td>
			<td>Fine Science Tools</td>
			<td>14058-11</td>
			<td>Different brand of a similar type will work</td>
		</tr>
		<tr>
			<td>Straight fine tip forceps</td>
			<td>Fine Science Tools</td>
			<td>11050-10</td>
			<td>Different brand of a similar type will work</td>
		</tr>
		<tr>
			<td>Curved medium tip forceps</td>
			<td>Fisher</td>
			<td>16100110</td>
			<td>Different brand of a similar type will work</td>
		</tr>
		<tr>
			<td>Scalpel handle</td>
			<td>Fine Science Tools</td>
			<td>10003-12</td>
			<td>Different brand of a similar type will work</td>
		</tr>
		<tr>
			<td>Mouse anti-SYCP3</td>
			<td>Abcam</td>
			<td>ab97672</td>
			<td>Use at 1:300</td>
		</tr>
		<tr>
			<td>Anti-centromere protein (derived from human CREST patient serum)</td>
			<td>Antibodies Incorporated</td>
			<td>15-234-0001</td>
			<td>Use at 1:50</td>
		</tr>
		<tr>
			<td>Humidified chamber</td>
			<td></td>
			<td></td>
			<td>We use Nunc square culture dishes 500 cm2/well with moistened paper towels</td>
		</tr>
		<tr>
			<td>Widefield microscope with epifluorescence</td>
			<td>Leica microsystems</td>
			<td></td>
			<td>Any standard model</td>
		</tr>
		<tr>
			<td>Coplin jars</td>
			<td>Several commercial brands</td>
			<td></td>
			<td>50 ml capacity; 40 mm (1.6 in.) diameter, holds 10 slides (back to back)</td>
		</tr>
		<tr>
			<td>Petri dishes</td>
			<td>Several commercial brands</td>
			<td></td>
			<td>100 x 15 mm diameter, polystyrene sterile untreated</td>
		</tr>
	</tbody>
</table>

preparation of meiotic chromosome spreads from mouse spermatocytes

Mammalian meiosis is a dynamic developmental process that occurs in germ cells and can be studied and characterized. Using a method to spread nuclei on the surface of slides (rather than dropping them from a height), we demonstrate an optimized technique on mouse spermatocytes that was first described in 1997. This method is widely used in laboratories to study mammalian meiosis because it yields a plethora of high quality nuclei undergoing substages of prophase I. Seminiferous tubules are first placed in a hypotonic solution to swell spermatocytes. Then spermatocytes are released into a sucrose solution to create a cell suspension, and nuclei are spread onto fixative-soaked glass slides. Following immunostaining, a diversity of proteins germane to meiotic processes can be examined. For example, proteins of the synaptonemal complex, a tripartite structure that connects the chromosome axes/cores of homologs together can be easily visualized. Meiotic recombination proteins, which are involved in repair of DNA double-strand breaks by homologous recombination, can also be immunostained to evaluate progression of prophase I. Here we describe and demonstrate in detail a technique widely used to study mammalian meiosis in spermatocytes from juvenile or adult male mice.

The ability of this method to provide large numbers of surface spread nuclei containing intact homologs depends on three main factors: 1) appropriate incubation time of seminiferous tubules in hypotonic buffer (i.e. HEB) to obtain adequately swelled spermatocyte nuclei that burst but do not disintegrate from prolonged incubation in HEB, 2) micropipetting the sucrose droplets of cells to obtain a separated suspension of nuclei that are not clumped together, and 3) tilting each fixative coa...

Watch this Scientific Journal Video about Preparation of Meiotic Chromosome Spreads from Mouse Spermatocytes at JoVE.com

Preparation of Meiotic Chromosome Spreads from Mouse Spermatocytes

Meiosis is the developmental process by which gametes are formed through a single round of DNA replication and two successive rounds of chromosome segregation. Mammalian meiosis can be examined by utilizing a technique to prepare meiotic chromosome spreads. Here, we demonstrate a method of preparing surface-spread nuclei from mouse spermatocytes.

Mammalian meiosis is a dynamic developmental process that occurs in germ cells and can be studied and characterized. Using a method to spread nuclei on ...

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11.7K Views.  Drexel University College of Medicine. Meiosis is the developmental process by which gametes are formed through a single round of DNA replication and two successive rounds of chromosome segregation. Mammalian meiosis can be examined by utilizing a technique to prepare meiotic chromosome spreads. Here, we demonstrate a method of preparing surface-spread nuclei from mouse spermatocytes.

Video: Preparation of Meiotic Chromosome Spreads from Mouse Spermatocytes

Preparation of Dissociated Mouse Cortical Neuron Cultures

This video will guide you through the process for generating cortical neuronal cultures from late embryo and early postnatal mouse brain. These cultures can be used for a variety of applications including immunocytochemistry, biochemistry, electrophysiology, calcium and sodium imaging, protein and/or RNA isolation. These cultures also provide a platform to study the neuronal development of transgenic animals that carry a late embryonic or postnatal lethal gene mutation. The procedure is relatively straight forward, requires some experience in tissue culture technique and should not take longer than two to three hours if you are properly prepared. Careful separation of the cortical rind from the thalamo-cortical fiber tract will reduce the number of unwanted non-neuronal cells. To increase yields of neuronal cells triturate the pieces of the cortical tissue gently after the enzyme incubation step. This is imperative as it prevents unnecessary injury to cells and premature neuronal cell death. Since these cultures are maintained in the absence of glia feeder cells, they also offer an added advantage of growing cultures enriched in neurons.

This video shows a procedure for generating neuronal cultures from late embryo and early postnatal mouse cortex. These cultures can be used for immunocytochemistry, biochemistry, electrophysiology, calcium and sodium imaging and provide a platform to study the neuronal development of transgenic animals that carry a postnatal lethal gene mutation.

This video will guide you through the process for generating cortical neuronal cultures from late embryo and early postnatal mouse brain. These cultures ...

Preparation of Single-Cell Suspensions from Mouse Spleen with the gentleMACS Dissociator

Single-cell suspensions are a prerequisite for experiments in cell separation, cell analysis and cell culture.  To avoid tedious and often painful manual dissociations the gentleMACS Dissociator allows one to dissociate tissue very efficiently under controlled and reproducible conditions.  The gentleMACS Dissociator can optimally dissociate mouse spleen, combining timesaving and standardization with user-safety.

This video describes how to dissociate mouse spleens using the gentleMACS Dissociator, an automated bench-top device that can mechanically disrupt tissues using special tubes to produce viable cell suspensions. Following dissociation, spleens are filtered, centrifuged, and resuspended for further applications.

This video describes a simple, time-saving technique for automated tissue dissociation using the gentleMACS Dissociator to prepare single-cell suspensions of mouse splenocytes.

Single-cell suspensions are a prerequisite for experiments in cell separation, cell analysis and cell culture.  To avoid tedious and often painful manual ...

Standardized Preparation of Single-Cell Suspensions from Mouse Lung Tissue using the gentleMACS Dissociator

The preparation of single-cell suspensions from tissues is an important prerequisite for many experiments in cellular research. The process of dissociating whole organs requires specific parameters in order to obtain a high number of viable cells in a reproducible manner. The gentleMACS Dissociator optimizes this task with a simple, practical protocol. The instrument contains pre-programmed settings that are optimized for the efficient but gentle dissociation of a variety of tissue types, including mouse lungs. In this publication the use of the gentleMACS Dissociator on lung tissue derived from mice is demonstrated.

Dissociating cells from specific tissue types requires specific parameters for tissue agitation to obtain a high volume of viable, culturable cells. The Miltenyi gentleMACS dissociator optimizes this task with a simple, practical protocol. In this publication the use of this apparatus on lung tissue is explained.

The preparation of single-cell suspensions from tissues is an important prerequisite for many experiments in cellular research. The process of ...

Preparation of Drosophila Polytene Chromosome Squashes for Antibody Labeling

Drosophila has long been a favorite model system for studying the relationship between chromatin structure and gene regulation due to the cytological advantages provided by the giant salivary gland polytene chromosomes of third instar larvae.  In this tissue the chromosomes undergo many rounds of replication in the absence of cell division giving rise to approximately 1000 copies.  The DNA remains aligned after each replicative cycle resulting in greatly enlarged chromosomes that provide a unique opportunity to correlate chromatin morphology with the localization of specific proteins.  Consequently, there has been a high level of interest in defining the epigenetic modifications present at different genes and at different stages of the transcription process. An important tool for such studies is the labeling of polytene chromosomes with antibodies to the enzyme, transcription factor, or histone modification of interest. This video protocol illustrates the squash technique used in the Johansen laboratory to prepare Drosophila polytene chromosomes for antibody labeling.

This video protocol illustrates the squash technique used in the Johansen laboratory to prepare Drosophila polytene chromosomes for antibody labeling.

Drosophila has long been a favorite model system for studying the relationship between chromatin structure and gene regulation due to the cytological ...

In vivo Imaging and Therapeutic Treatments in an Orthotopic Mouse Model of Ovarian Cancer

Human cancer and response to therapy is better represented in orthotopic animal models. This paper describes the development of an orthotopic mouse model of ovarian cancer, treatment of cancer via oral delivery of drugs, and monitoring of tumor cell behavior in response to drug treatment in real time using in vivo imaging system. In this orthotopic model, ovarian tumor cells expressing luciferase are applied topically by injecting them directly into the mouse bursa where each ovary is enclosed. Upon injection of D-luciferin, a substrate of firefly luciferase, luciferase-expressing cells generate bioluminescence signals. This signal is detected by the in vivo imaging system and allows for a non-invasive means of monitoring tumor growth, distribution, and regression in individual animals. Drug administration via oral gavage allows for a maximum dosing volume of 10 mL/kg body weight to be delivered directly to the stomach and closely resembles delivery of drugs in clinical treatments. Therefore, techniques described here, development of an orthotopic mouse model of ovarian cancer, oral delivery of drugs, and in vivo imaging, are useful for better understanding of human ovarian cancer and treatment and will improve targeting this disease.

In vivo Imaging and Therapeutic Treatments in an Orthotopic Mouse Model of Ovarian Cancer

Orthotopic animal models of ovarian cancer replicate better human disease and therefore enhance our understanding of cancer progression and tumor response to therapy. A mouse model receives an intrabursal injection of luciferase-expressing ovarian tumor cells. Treatment is administered via oral gavage. Tumor growth is monitored by in vivo imaging system.

Human cancer and response to therapy is better represented in orthotopic animal models.  This paper describes the development of an orthotopic mouse model ...

Flow Cytometry Purification of Mouse Meiotic Cells

The heterogeneous nature of cell types in the testis and the absence of meiotic cell culture models have been significant hurdles to the study of the unique differentiation programs that are manifest during meiosis. Two principal methods have been developed to purify, to varying degrees, various meiotic fractions from both adult and immature animals: elutriation or Staput (sedimentation) using BSA and/or percoll gradients. Both of these methods rely on cell size and density to separate meiotic cells1-5. Overall, except for few cell populations6, these protocols fail to yield sufficient purity of the numerous meiotic cell populations that are necessary for detailed molecular analyses. Moreover, with such methods usually one type of meiotic cells can be purified at a given time, which adds an extra level of complexity regarding the reproducibility and homogeneity when comparing meiotic cell samples.
Here, we describe a refined method that allows one to easily visualize, identify, and purify meiotic cells, from germ cells to round spermatids, using FACS combined with Hoechst 33342 staining7,8. This method provides an overall snapshot of the entire meiotic process and allows one to highly purify viable cells from most stage of meiosis. These purified cells can then be analyzed in detail for molecular changes that accompany progression through meiosis, for example changes in gene expression9,10and the dynamics of nucleosome occupancy at hotspots of meiotic recombination11.

An efficient method to obtain highly purified viable meiotic fractions from mouse testis is described, which combines a refined cell dissociation protocol with fluorescent activated cell sorting (FACS). This method takes advantage of differences in the DNA content and nuclear density of discrete meiotic fractions.

The heterogeneous nature of cell types in the testis and the absence of meiotic cell culture models have been significant hurdles to the study of the ...

Generation of Mice Derived from Induced Pluripotent Stem Cells

The production of induced pluripotent stem cells (iPSCs) from somatic cells provides a means to create valuable tools for basic research and may also produce a source of patient-matched cells for regenerative therapies. iPSCs may be generated using multiple protocols and derived from multiple cell sources. Once generated, iPSCs are tested using a variety of assays including immunostaining for pluripotency markers, generation of three germ layers in embryoid bodies and teratomas, comparisons of gene expression with embryonic stem cells (ESCs) and production of chimeric mice with or without germline contribution2. Importantly, iPSC lines that pass these tests still vary in their capacity to produce different differentiated cell types2. This has made it difficult to establish which iPSC derivation protocols, donor cell sources or selection methods are most useful for different applications.
The most stringent test of whether a stem cell line has sufficient developmental potential to generate all tissues required for survival of an organism (termed full pluripotency) is tetraploid embryo complementation (TEC)3-5. Technically, TEC involves electrofusion of two-cell embryos to generate tetraploid (4n) one-cell embryos that can be cultured in vitro to the blastocyst stage6. Diploid (2n) pluripotent stem cells (e.g. ESCs or iPSCs) are then injected into the blastocoel cavity of the tetraploid blastocyst and transferred to a recipient female for gestation (see Figure 1). The tetraploid component of the complemented embryo contributes almost exclusively to the extraembryonic tissues (placenta, yolk sac), whereas the diploid cells constitute the embryo proper, resulting in a fetus derived entirely from the injected stem cell line.
Recently, we reported the derivation of iPSC lines that reproducibly generate adult mice via TEC1. These iPSC lines give rise to viable pups with efficiencies of 5-13%, which is comparable to ESCs3,4,7 and higher than that reported for most other iPSC lines8-12. These reports show that direct reprogramming can produce fully pluripotent iPSCs that match ESCs in their developmental potential and efficiency of generating pups in TEC tests. At present, it is not clear what distinguishes between fully pluripotent iPSCs and less potent lines13-15. Nor is it clear which reprogramming methods will produce these lines with the highest efficiency. Here we describe one method that produces fully pluripotent iPSCs and "all- iPSC" mice, which may be helpful for investigators wishing to compare the pluripotency of iPSC lines or establish the equivalence of different reprogramming methods.

Generating induced pluripotent stem cell (iPSC) lines produces lines of differing developmental potential even when they pass standard tests for pluripotency. Here we describe a protocol to produce mice derived entirely from iPSCs, which defines the iPSC lines as possessing full pluripotency1.

The production of induced pluripotent stem cells (iPSCs) from somatic cells provides a means to create valuable tools for basic research and may also ...

Chromosome Preparation From Cultured Cells

Chromosome (cytogenetic) analysis is widely used for the detection of chromosome instability. When followed by G-banding and molecular techniques such as fluorescence in situ hybridization (FISH), this assay has the powerful ability to analyze individual cells for aberrations that involve gains or losses of portions of the genome&#160;and rearrangements involving one or more chromosomes. In humans, chromosome abnormalities occur in approximately 1 per 160 live births1,2, 60-80% of all miscarriages3,4, 10% of stillbirths2,5, 13% of individuals with congenital heart disease6, 3-6% of infertility cases2, and in many patients with developmental delay&#160;and birth defects7. Cytogenetic analysis of malignancy is routinely used by researchers and clinicians, as observations of clonal chromosomal abnormalities have been shown to have both diagnostic and prognostic significance8,9.&#160; Chromosome isolation is invaluable for gene therapy and stem cell research of organisms including nonhuman primates and rodents10-13.
Chromosomes can be isolated from cells of live tissues, including blood lymphocytes, skin fibroblasts, amniocytes, placenta, bone marrow, and tumor specimens. Chromosomes are analyzed at the metaphase stage of mitosis, when they are most condensed and therefore more clearly visible. The first step of the chromosome isolation technique involves the disruption of the spindle fibers by incubation with Colcemid, to prevent the cells from proceeding to the subsequent anaphase stage. The cells are then treated with a hypotonic solution and preserved in their swollen state with Carnoy&#39;s fixative. The cells are then dropped on to slides and can then be utilized for a variety of procedures. G-banding involves trypsin treatment followed by staining with Giemsa to create characteristic light and dark bands. The same procedure to isolate chromosomes can be used for the preparation of cells for procedures such as fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH), and spectral karyotyping (SKY)14,15.

Chromosomes can be isolated from live cells such as lymphocytes or skin fibroblasts, and from organisms including humans or mice. These chromosome preparations can be further utilized for routine G-banding and molecular cytogenetic procedures such as fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH), and spectral karyotyping (SKY).

Chromosome (cytogenetic) analysis is widely used for the detection of chromosome instability. When followed by G-banding and molecular techniques such as ...

A Fast Air-dry Dropping Chromosome Preparation Method Suitable for FISH in Plants

Preparation of chromosome spreads is a prerequisite for the successful performance of fluorescence in situ hybridization (FISH). Preparation of high quality plant chromosome spreads is challenging due to the rigid cell wall. One of the approved methods for the preparation of plant chromosomes is a so-called drop preparation, also known as drop-spreading or air-drying technique. Here, we present a protocol for the fast preparation of mitotic chromosome spreads suitable for the FISH detection of single and high copy DNA probes. This method is an improved variant of the air-dry drop method performed under a relative humidity of 50%-55%. This protocol comprises a reduced number of washing steps making its application easy, efficient and reproducible. Obvious benefits of this approach are well-spread, undamaged and numerous metaphase chromosomes serving as a perfect prerequisite for successful FISH analysis. Using this protocol we obtained high-quality chromosome spreads and reproducible FISH results for Hordeum vulgare, H. bulbosum, H. marinum, H. murinum, H. pubiflorum and Secale cereale.

A protocol is described for the preparation of high-quality mitotic plant chromosome spreads by a fast air-dry dropping method suitable for the FISH detection of single and high copy DNA probes.

Preparation of chromosome spreads is a prerequisite for the successful performance of fluorescence in situ hybridization (FISH). Preparation of high ...

Meiotic Spindle Assessment in Mouse Oocytes by siRNA-mediated Silencing

Errors in chromosome segregation during meiotic division in gametes can lead to aneuploidy that is subsequently transmitted to the embryo upon fertilization. The resulting aneuploidy in developing embryos is recognized as a major cause of pregnancy loss and congenital birth defects such as Down&#8217;s syndrome. Accurate chromosome segregation is critically dependent on the formation of the microtubule spindle apparatus, yet this process remains poorly understood in mammalian oocytes. Intriguingly, meiotic spindle assembly differs from mitosis and is regulated, at least in part, by unique microtubule organizing centers (MTOCs). Assessment of MTOC-associated proteins can provide valuable insight into the regulatory mechanisms that govern meiotic spindle formation and organization. Here, we describe methods to isolate mouse oocytes and deplete MTOC-associated proteins using a siRNA-mediated approach to test function. In addition, we describe oocyte fixation and immunofluorescence analysis conditions to evaluate meiotic spindle formation and organization.

Here, we present a protocol for specific siRNA-mediated mRNA depletion followed by immunofluorescence analysis to evaluate meiotic spindle assembly and organization in mouse oocytes. This protocol is suitable for in vitro depletion of transcripts and functional assessment of different spindle and/or MTOC-associated factors in oocytes.