This project was supported in part by monies from the State of Florida to Scripps and award numbers R01GM085079 and R21HD061304 from the National Institute of General Medical Sciences and the National Institute of Child Health and Human Development, respectively. This is manuscript number 20917 of The Scripps Research Institute.

This protocol can be separated in two major steps: (1) the dissociation and Hoechst 33342 staining of mouse testis cells followed by, if necessary, (2) FACS sorting of the relevant meiotic fractions, including all stages of meiosis, from germ cells to round spermatids. Once collected, these highly enriched meiotic populations can be used for a wide range of analysis. This protocol describes the dissociation of one adult testis; volumes can be adapted accordingly for juveniles or for additional testes.
1. Testis Dissociation
<ol>
	<li>Place one decapsulated testis in a 15-ml tube.</li>
	<li>Add 3-ml of Gey's Balance Salt Solution (GBSS) containing 120 U/ml of Collagenase type I.</li>
	<li>Add 10 &mu;l of DNAse I (1mg/ml stock solution in 50% glycerol) and shake it vigorously by hand until you see testicular tubules starting to dissociate.</li>
	<li>Agitate horizontally at a maximum of 120 rpm for 15 min at 33&deg;C.</li>
	<li>Decant for 1 min vertically at room temperature and discard supernatant.</li>
	<li>Repeat steps 1.2 to 1.5.</li>
	<li>Add 2.5 ml of GBSS containing Collagenase type I, 50 &mu;l of a 50mg/ml Trypsin stock solution resuspended in 1mM HCl solution, and 10 &mu;l of DNAse I (1mg/ml), and invert the tube several times.</li>
	<li>Agitate horizontally at a maximum of 120 rpm for 15 min at 33&deg;C.</li>
	<li>Using plastic disposable Pasteur pipet with wide orifice, pipette gently up and down for 3 min.No clumps should be visible at this point.</li>
	<li>Add 30 &mu;l of trypsin, 10 &mu;l of DNAse I, 40 &mu;l of Hoechst 33342 resuspended in DMSO (10 mg/ml), and invert the tube several times.</li>
	<li>Agitate horizontally at a maximum of 120 rpm for 15 min at 33&deg;C.</li>
	<li>Add 400-&mu;l of fetal calf serum (FCS) and mix by inverting to inactivate trypsin.</li>
	<li>Final staining is performed by adding 50 &mu;l of Hoechst 33342 resuspended in DMSO (10 mg/ml), and 10 &mu;l of DNAse I (1 mg/ml).</li>
	<li>Agitate horizontally at a maximum of 120 rpm for 15 min at 33&deg;C.</li>
	<li>The dissociated testis sample is then passed through two 40-&mu;m GBSS pre-wetted disposable filters over a 50-ml conical tube, then 5 &mu;l of propidium iodide (PI) solution is added and sample is gently mixed by pipetting several times with disposable Pasteur pipette.</li>
	<li>Sample is transferred to a 5-ml plastic syringe through an 18-gauge needle. The latter is replaced by a 22-gauge needle for sample delivery. The syringe is stored on ice and protected from the light until ready for FACS processing.</li>
</ol>
2. FACS Setup and Purification
<ol>
	<li>Sorting was performed on a Becton-Dickinson Aria IIu cell sorter. The conditions described should therefore be used as a starting point especially when using different equipment. We used conditions previously described7,8.</li>
	<li>Since the Aria IIu does not have a UV laser, we adapted the protocol for detecting Hoescht staining using a 405nm violet laser in addition we used a 488nm blue laser for forward and side scatter detection. Furthermore, some filters were modified in order to limit some red laser leakiness resulting in improved scattered plot sharpness.</li>
	<li>The violet laser was configured with a 450/40nm band pass for detection of Hoescht Blue emission and a 585/42nm band pass for Hoescht Red emission. A 502nm long pass was used to separate blue from red fluorescence.</li>
	<li>A 100 &mu;m nozzle was used with a drop drive frequency of 28,000 drops/second. The sample threshold rate was approximately 4000 events/second. The temperature control option was used to maintain sample and collection tubes at 4&deg;C the entire duration of sorting. Additionally, the sample agitation feature was used at 200 rpm to prevent the sample from sedimenting throughout the sort.</li>
	<li>Usually, two to three testes were processed per 6 hours sort allowing the collection of 0.5- 2.0x106cells for each population (see representative section).</li>
	<li>The sample was sorted in aliquots of approximately 750&mu;l dispensed from the syringe. Meanwhile, during these pauses the collection tubes were kept at 4&deg;C, protected from the light, and gently mixed prior to resuming sort.</li>
	<li>The sorted samples were collected into a 12x75mm glass borosilicated collection tube containing 250&mu;l DMEM supplemented with 10% FCS.</li>
</ol>
3. Representative Results:
A typical FACS profile is shown in Figure 1. All of the major steps of meiosis are identified and are indicated in the legend. If the Hoechst 33342 stain is not optimal, the global profile will appear much more compact and less defined. A common problem regards not adding sufficient DNAse, which will induce rapid cell clumping. Addition of extra DNAse at all indicted steps usually solves this problem. Freeze thawing of the DNAse stock (stored at -20&deg;C)should be kept to a minimum, as this results in rapid loss of enzyme activity.
Spo11 is the meiotic endonuclease that directs double-strand breaks at sites of meiotic recombination hotspots12.Figure 2 shows typical profiles of a Spo11-null testis where double-strand break are not formed, resulting in an abortive meiosis12, as well as a pre-puberous profile of a 13-days old mouse, which reveals asynchronous nature of this first wave of meiosis. Standard cytogenetic analyses using the combination of synaptonemal complex protein 3 (SCP3) and phosphorylated histone H2AX antibodies stage-specific meiosis markers should be initially used to confirmed the purity and nature of the sorted meiotic cells, as described elswhere11.
<img src="/files/ftp_upload/2602/2602fig1.jpg" alt="Figure 1" /> 
Figure 1. Wild-type meiosis FACS profiles. A) Representative scatter plot is shown. The gated cells are shown. Note the large amount of debris present in adult testis containing mostly empty membranes and spermatid tails. B) A representative PI plot shows the very limited amount of PI positive cells present in a sample. The typical gate is shown. C) A representative wild-type Hoechst 33342 FACS profile is shown. The various meiotic cell populations that can be purified using this method for further study are indicated: spermatogonia (Sp), pre-leptotene (pL), leptotene-zygotene (L/Z), early-Pachytene (eP), middle-Pachytene (mP), late-Pachytene (lP), diplotene (D), and round spermatids (RS).
<img src="/files/ftp_upload/2602/2602fig2.jpg" alt="Figure 2" /> 
Figure 2. Spo11-null and wild-type day 13 meiotic FACS profiles. A) A typical Spo11-null profile is shown with a clear meiotic failure, where no stage past the leptotene/zygotene early-pachytene can be detected. B) The profile of a 13-day-old wild-type male mouse shows the high concentration of leptotene/zygotene cells. This first wave of meiosis is rather asynchronous, as clearly visualized using this methodology.

<ol>
	<li>Meistrich, M. L., Bruce, W. R., Clermont, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+composition+of+fractions+of+mouse+testis+cells+following+velocity+sedimentation+separation.">Cellular composition of fractions of mouse testis cells following velocity sedimentation separation.</a> Exp. Cell Res. 79, 213-227 (1973).</li><li>Grabske, R. J., Lake, S., Gledhill, B. L., Meistrich, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Centrifugal+elutriation:+separation+of+spermatogenic+cells+on+the+basis+of+sedimentation+velocity.">Centrifugal elutriation: separation of spermatogenic cells on the basis of sedimentation velocity.</a> J. Cell. Physiol. 86, 177-189 (1975).</li><li>Purification, A. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=culture,+and+fractionation+of+spermatogenic+cells.">culture, and fractionation of spermatogenic cells.</a> Methods Enzymol. 225, 84-113 (1993).</li><li>Romrell, L. J., Bellve, A. R., Fawcett, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Separation+of+mouse+spermatogenic+cells+by+sedimentation+velocity.+A+morphological+characterization.">Separation of mouse spermatogenic cells by sedimentation velocity. A morphological characterization.</a> Dev. Biol. 49, 119-131 (1976).</li><li>Meistrich, M. L., Trostle, P. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Separation+of+mouse+testis+cells+by+equilibrium+density+centrifugation+in+renografin+gradients.">Separation of mouse testis cells by equilibrium density centrifugation in renografin gradients.</a> Exp. Cell Res. 92, 231-244 (1975).</li><li>Namekawa, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Postmeiotic+sex+chromatin+in+the+male+germline+of+mice.">Postmeiotic sex chromatin in the male germline of mice.</a> Curr. Biol. 16, 660-667 (2006).</li><li>Lassalle, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Side+Population'+cells+in+adult+mouse+testis+express+Bcrp1+gene+and+are+enriched+in+spermatogonia+and+germinal+stem+cells.">Side Population' cells in adult mouse testis express Bcrp1 gene and are enriched in spermatogonia and germinal stem cells.</a> Development. 131, 479-487 (2004).</li><li>Bastos, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flow+cytometric+characterization+of+viable+meiotic+and+postmeiotic+cells+by+Hoechst+33342+in+mouse+spermatogenesis.">Flow cytometric characterization of viable meiotic and postmeiotic cells by Hoechst 33342 in mouse spermatogenesis.</a> Cytometry A. 65, 40-49 (2005).</li><li>Chowdhury, R., Bois, P. R., Feingold, E., Sherman, S. L., Cheung, V. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+analysis+of+variation+in+human+meiotic+recombination.">Genetic analysis of variation in human meiotic recombination.</a> PLoS Genet. 5, e1000648-e1000648 (2009).</li><li>Roig, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mouse+TRIP13/PCH2+is+required+for+recombination+and+normal+higher-order+chromosome+structure+during+meiosis.">Mouse TRIP13/PCH2 is required for recombination and normal higher-order chromosome structure during meiosis.</a> PLoS Genet. 6, (2010).</li><li>Getun, I. V., Wu, Z. K., Khalil, A. M., Bois, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nucleosome+occupancy+landscape+and+dynamics+at+mouse+recombination+hotspots.">Nucleosome occupancy landscape and dynamics at mouse recombination hotspots.</a> EMBO Rep. 11, 555-560 (2010).</li><li>Romanienko, P. J., Camerini-Otero, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mouse+Spo11+gene+is+required+for+meiotic+chromosome+synapsis.">The mouse Spo11 gene is required for meiotic chromosome synapsis.</a> Mol. Cell. 6, 975-987 (2000).</li></ol>

No conflicts of interest declared.

The protocol presented herein allows one to simultaneously purify from adult male mice the entire range of the meiotic stage cells with very high purity, allowing investigators to study the dynamics of this fundamental process. Purified cells can be used for numerous applications ranging from RNA extraction9,10, nucleosome mapping11, recombinant molecule detection, protein analyses, and many more. However, detection methods have to be adapted to the amount of meiotic cells purified. Moreover, with t...

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		<tr>
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		<th>Catalogue Number</th>
		<th>Comment</th>
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		<tbody>
		
<tr>
<td>Collagenase Type-1</td>
<td>&nbsp;</td>
<td>Worthington</td>
<td>CLSS1</td>
<td>Dissolve to 12,000U/ml in GBSS, store at 4&deg;C</td>
</tr>
<tr>
<td>Trypsin</td>
<td>&nbsp;</td>
<td>Worthington</td>
<td>TRL3</td>
<td>Dissolve in 1mM HCl to 50mg/ml, store at 4&deg;C</td>
</tr>
<tr>
<td>Hoechst 33342</td>
<td>&nbsp;</td>
<td>Arcos</td>
<td>230001000</td>
<td>Saturated solution (10mg/ml in DMSO, store at 4&deg;C</td>
</tr>
<tr>
<td>DNAse I</td>
<td>&nbsp;</td>
<td>Sigma-Aldrich</td>
<td>DNEP</td>
<td>Dissolve in water/50% glycerol to 1mg/ml, store at -20&deg;C</td>
</tr>
<tr>
<td>Gey&#x2019;s Balance Salt Solution </td>
<td>&nbsp;</td>
<td>Sigma-Aldrich</td>
<td>G9779</td>
<td>&nbsp;</td>
<tr>
<td>6" Transfer Pipet</td>
<td>&nbsp;</td>
<td>Fisher Scientific</td>
<td>137119D</td>
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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.

Watch this Scientific Journal Video about Flow Cytometry Purification of Mouse Meiotic Cells at JoVE.com

Flow Cytometry Purification of Mouse Meiotic Cells

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 ...

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17.6K Views.  The Scripps Research Institute. 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.

Video: Flow Cytometry Purification of Mouse Meiotic Cells

Flow Cytometry-based Purification of S. cerevisiae Zygotes

Zygotes are essential intermediates between haploid and diploid states in the life cycle of many organisms, including yeast (Figure 1) 1. S. cerevisiae zygotes result from the fusion of haploid cells of distinct mating type (MATa, MATalpha) and give rise to corresponding stable diploids that successively generate as many as 20 diploid progeny as a result of their strikingly asymmetric mitotic divisions 2. Zygote formation is orchestrated by a complex sequence of events: In this process, soluble mating factors bind to cognate receptors, triggering receptor-mediated signaling cascades that facilitate interruption of the cell cycle and culminate in cell-cell fusion. Zygotes may be considered a model for progenitor or stem cell function.
Although much has been learned about the formation of zygotes and although zygotes have been used to investigate cell-molecular questions of general significance, almost all studies have made use of mating mixtures in which zygotes are intermixed with a majority population of haploid cells 3-8. Many aspects of the biochemistry of zygote formation and the continuing life of the zygote therefore remain uninvestigated.
Reports of purification of yeast zygotes describe protocols based on their sedimentation properties 9; however, this sedimentation-based procedure did not yield nearly 90% purity in our hands. Moreover, it has the disadvantage that cells are exposed to hypertonic sorbitol. We therefore have developed a versatile purification procedure. For this purpose, pairs of haploid cells expressing red or green fluorescent proteins were co-incubated to allow zygote formation, harvested at various times, and the resulting zygotes were purified using a flow cytometry-based sorting protocol. This technique provides a convenient visual assessment of purity and maturation. The average purity of the fraction is approximately 90%. According to the timing of harvest, zygotes of varying degrees of maturity can be recovered. The purified samples provide a convenient point of departure for "-omic" studies, for recovery of initial progeny, and for systematic investigation of this progenitor cell.

Flow Cytometry-based Purification of S. cerevisiae Zygotes

To purify zygotes of S. cerevisiae, haploid cells of opposite mating type were engineered to express red or green fluorescent proteins, co-incubated to allow zygote formation, and fractionated using a flow cytometry-based protocol. The highly-enriched fraction enables subsequent "-omic" studies, recovery of initial progeny, and systematic investigation of zygote morphogenesis.

Zygotes are essential intermediates between haploid and diploid states in the life cycle of many organisms, including yeast (Figure 1) 1. S. cerevisiae ...

Optimized Staining and Proliferation Modeling Methods for Cell Division Monitoring using Cell Tracking Dyes

Fluorescent cell tracking dyes, in combination with flow and image cytometry, are powerful tools with which to study the interactions and fates of different cell types in vitro and in vivo.1-5 Although there are literally thousands of publications using such dyes, some of the most commonly encountered cell tracking applications include monitoring of:
<ol>
	<li>stem and progenitor cell quiescence, proliferation and/or differentiation6-8</li>
	<li>antigen-driven membrane transfer9 and/or precursor cell proliferation3,4,10-18 and</li>
	<li>immune regulatory and effector cell function1,18-21.</li>
</ol>
Commercially available cell tracking dyes vary widely in their chemistries and fluorescence properties but the great majority fall into one of two classes based on their mechanism of cell labeling. "Membrane dyes", typified by PKH26, are highly lipophilic dyes that partition stably but non-covalently into cell membranes1,2,11. "Protein dyes", typified by CFSE, are amino-reactive dyes that form stable covalent bonds with cell proteins4,16,18. Each class has its own advantages and limitations. The key to their successful use, particularly in multicolor studies where multiple dyes are used to track different cell types, is therefore to understand the critical issues enabling optimal use of each class2-4,16,18,24.
The protocols included here highlight three common causes of poor or variable results when using cell-tracking dyes. These are:
<ol>
	<li>Failure to achieve bright, uniform, reproducible labeling. This is a necessary starting point for any cell tracking study but requires attention to different variables when using membrane dyes than when using protein dyes or equilibrium binding reagents such as antibodies.</li>
	<li>Suboptimal fluorochrome combinations and/or failure to include critical compensation controls. Tracking dye fluorescence is typically 102 - 103 times brighter than antibody fluorescence. It is therefore essential to verify that the presence of tracking dye does not compromise the ability to detect other probes being used.</li>
	<li>Failure to obtain a good fit with peak modeling software. Such software allows quantitative comparison of proliferative responses across different populations or stimuli based on precursor frequency or other metrics. Obtaining a good fit, however, requires exclusion of dead/dying cells that can distort dye dilution profiles and matching of the assumptions underlying the model with characteristics of the observed dye dilution profile.</li>
</ol>
Examples given here illustrate how these variables can affect results when using membrane and/or protein dyes to monitor cell proliferation.

Successful use of cell tracking dyes to monitor immune cell function and proliferation involves several critical steps. We describe methods for: 1) obtaining bright, uniform, reproducible label-ing with membrane dyes; 2) selecting fluorochromes and data acquisition conditions; and 3) choosing a model to quantify cell proliferation based on dye dilution.

Fluorescent cell tracking dyes, in combination with flow and image cytometry, are powerful tools with which to study the interactions and fates of ...

Cytosolic Calcium Measurements in Renal Epithelial Cells by Flow Cytometry

A variety of cellular processes, both physiological and pathophysiological, require or are governed by calcium, including exocytosis, mitochondrial function, cell death, cell metabolism and cell migration to name but a few. Cytosolic calcium is normally maintained at low nanomolar concentrations; rather it is found in high micromolar to millimolar concentrations in the endoplasmic reticulum, mitochondrial matrix and the extracellular compartment. Upon stimulation, a transient increase in cytosolic calcium serves to signal downstream events. Detecting changes in cytosolic calcium is normally performed using a live cell imaging set up with calcium binding dyes that exhibit either an increase in fluorescence intensity or a shift in the emission wavelength upon calcium binding. However, a live cell imaging set up is not freely accessible to all researchers. Alternative detection methods have been optimized for immunological cells with flow cytometry and for non-immunological adherent cells with a fluorescence microplate reader. Here, we describe an optimized, simple method for detecting changes in epithelial cells with flow cytometry using a single wavelength calcium binding dye. Adherent renal proximal tubule epithelial cells, which are normally difficult to load with dyes, were loaded with a fluorescent cell permeable calcium binding dye in the presence of probenecid, brought into suspension and calcium signals were monitored before and after addition of thapsigargin, tunicamycin and ionomycin.

Calcium is involved in numerous physiological and pathophysiological signaling pathways. Live cell imaging requires specialized equipment and can be time consuming. A quick, simple method using a flow cytometer to determine relative changes in cytosolic calcium in adherent epithelial cells brought into suspension was optimized.

A variety of cellular processes, both physiological and pathophysiological, require or are governed by calcium, including exocytosis, mitochondrial ...

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.

Errors in chromosome segregation during meiotic division in gametes can lead to aneuploidy that is subsequently transmitted to the embryo upon ...

LED Thermo Flow &#8212; Combining Optogenetics with Flow Cytometry

Optogenetic tools allow isolated, functional investigations of almost any signaling molecule within complex signaling pathways. A major obstacle is the controlled delivery of light to the cell sample and hence the most popular tools for optogenetic studies are microscopy-based cell analyses and in vitro experiments. The flow cytometer has major advantages over a microscope, including the ability to rapidly measure thousands of cells at single cell resolution. However, it is not yet widely used in optogenetics. Here, we present a device that combines the power of optogenetics and flow cytometry: the LED Thermo Flow. This device illuminates cells at specific wavelengths, light intensities and temperatures during flow cytometric measurements. It can be built at low cost and be used with most common flow cytometers. To demonstrate its utility, we characterized the photoswitching kinetics of Dronpa proteins in vivo and in real time. This protocol can be adapted to almost all optically controlled substances and substantially expands the set of possible experiments. More importantly, it will greatly simplify the discovery and development of new optogenetic tools.

LED Thermo Flow &amp;#8212; Combining Optogenetics with Flow Cytometry

Optically controlled substances are powerful tools to study signaling pathways. To expand the spectrum of possible experiments, we developed a device for studying optically controlled substances in real time using flow cytometry: the LED Thermo Flow.

Optogenetic tools allow isolated, functional investigations of almost any signaling molecule within complex signaling pathways. A major obstacle is the ...

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.

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 ...

Analysis of Cell Suspensions Isolated from Solid Tissues by Spectral Flow Cytometry

Flow cytometry has been used for the past 40 years to define and analyze the phenotype of lymphoid and other hematopoietic cells. Initially restricted to the analysis of a few fluorochromes, currently there are dozens of different fluorescent dyes, and up to 14-18 different dyes can be combined at a time. However, several limitations still impair the analytical capabilities. Because of the multiplicity of fluorescent probes, data analysis has become increasingly complex due to the need of large, multi-parametric compensation matrices. Moreover, mutant mouse models carrying fluorescent proteins to detect and trace specific cell types in different tissues have become available, so the analysis (by flow cytometry) of auto-fluorescent cell suspensions obtained from solid organs is required. Spectral flow cytometry, which distinguishes the shapes of emission spectra along a wide range of continuous wavelengths, addresses some of these problems. The data is analyzed with an algorithm that replaces compensation matrices and treats auto-fluorescence as an independent parameter. Thus, spectral flow cytometry should be capable of discriminating fluorochromes with similar emission peaks and can provide a multi-parametric analysis without compensation requirements.
This protocol describes the spectral flow cytometry analysis, allowing for a 21-parameter (19 fluorescent probes) characterization and the management of an auto-fluorescent signal, providing high resolution in minor population detection. The results presented here show that spectral flow cytometry presents advantages in the analysis of cell populations from tissues difficult to characterize in conventional flow cytometry, such as the heart and the intestine. Spectral flow cytometry thus demonstrates the multi-parametric analytical capacity of high-performing conventional flow cytometry without the requirement for compensation and enables auto-fluorescence management.

This article describes spectral cytometry, a new approach in flow cytometry that uses the shapes of emission spectra to distinguish fluorochromes. An algorithm replaces compensations and can treat auto-fluorescence as an independent parameter. This new approach allows for the proper analysis of cells isolated from solid organs.

Flow cytometry has been used for the past 40 years to define and analyze the phenotype of lymphoid and other hematopoietic cells. Initially restricted to ...

Trans-inner Cell Mass Injection of Embryonic Stem Cells Leads to Higher Chimerism Rates

In an effort to increase efficiency in the creation of genetically modified mice via ES Cell methodologies, we present an adaptation to the current blastocyst injection protocol. Here we report that a simple rotation of the embryo, and injection through Trans-Inner cell mass (TICM) increased the percentage of chimeric mice from 31% to 50%, with no additional equipment or further specialized training. 26 different inbred clones, and 35 total clones were injected over a period of 9 months. There was no significant difference in either pregnancy rate or recovery rate of embryos between traditional injection techniques and TICM. Therefore, without any major alteration in the injection process and a simple positioning of the blastocyst and injecting through the ICM, releasing the ES cells into the blastocoel cavity can potentially improve the quantity of chimeric production and subsequent germline transmission.

Here we present a protocol to increase chimera production without the use of new equipment. A simple orientation change of the embryo for injection can increase the number of embryos produced, and potentially reduce the timeline to germline transmission.

In an effort to increase efficiency in the creation of genetically modified mice via ES Cell methodologies, we present an adaptation to the current ...

Isolation and Characterization of the Immune Cells from Micro-dissected Mouse Choroid Plexuses

The brain is no longer considered as an organ functioning in isolation; accumulating evidence suggests that changes in the peripheral immune system can indirectly shape brain function. At the interface between the brain and the systemic circulation, the choroid plexuses (CP), which constitute the blood-cerebrospinal fluid barrier, have been highlighted as a key site of periphery-to-brain communication. CP produce the cerebrospinal fluid, neurotrophic factors, and signaling molecules that can shape brain homeostasis. CP are also an active immunological niche. In contrast to the brain parenchyma, which is populated mainly by microglia under physiological conditions, the heterogeneity of CP immune cells recapitulates the diversity found in other peripheral organs. The CP immune cell diversity and activity change with aging, stress, and disease and modulate the activity of the CP epithelium, thereby indirectly shaping brain function. The goal of this protocol is to isolate murine CP and identify about 90% of the main immune subsets that populate them. This method is a tool to characterize CP immune cells and understand their function in orchestrating periphery-to-brain communication. The proposed protocol may help decipher how CP immune cells indirectly modulate brain function in health and across various disease conditions.

This study uses flow cytometry and two different gating strategies on isolated perfused mice brain choroid plexuses; this protocol identifies the main immune cell subsets that populate this brain structure.

The brain is no longer considered as an organ functioning in isolation; accumulating evidence suggests that changes in the peripheral immune system can ...

Isolation and Identification of Vascular Endothelial Cells from Distinct Adipose Depots for Downstream Applications

Vascular endothelial cells lining the wall of the vascular system play important roles in a variety of physiological processes, including vascular tone regulation, barrier functions, and angiogenesis. Endothelial cell dysfunction is a hallmark predictor and major driver for the progression of severe cardiovascular diseases, yet the underlying mechanisms remain poorly understood. The ability to isolate and perform analyses on endothelial cells from various vascular beds in their native form will give insight into the processes of cardiovascular disease. This protocol presents the procedure for the dissection of mouse subcutaneous and mesenteric adipose tissues, followed by isolation of their respective arterial vasculature. The isolated arteries are then digested using a specific cocktail of digestive enzymes focused on liberating functionally viable endothelial cells. The digested tissue is assessed by flow cytometry analysis using CD31+/CD45&#8722; cells as markers for positive endothelial cell identification. Cells can be sorted for immediate downstream functional assays or used to generate primary cell lines. The technique of isolating and digesting arteries from different vascular beds will provide options for researchers to evaluate freshly isolated vascular cells&#160;from arteries of interest and allow them to perform a wide range of functional tests on specific cell types.

This protocol details a method for the dissection of mouse adipose depots and the isolation and digestion of respective arteries to liberate and then identify the endothelial cell population. Freshly isolated cells used in downstream applications will advance the understanding of vascular cell biology and the mechanisms of vascular dysfunction.

Vascular endothelial cells lining the wall of the vascular system play important roles in a variety of physiological processes, including vascular tone ...