We thank C Zhang for fish care. This work was supported by the National Natural Science Foundation of China (31171074, 31371099 and 31571067 to GP) and by the Pujiang Talent Project (09PJ1401900 to GP).

Zebrafish experiments were approved by the Fudan University Institutional Animal Care and Use Committee. Zebrafish were raised and bred according to standard procedures20.
1. Preparations
<ol>
	<li>Cultivate 17 dpf and 25 dpf larval zebrafish
	<ol>
		<li>Transfer 2 male and 2 female adult zebrafish (healthy, 3 to 6 months old, laboratory AB strain) to a crossing tank in the late afternoon before the crossing day. Separate the males and females with a barrier. The next...

<ol>
	<li>Wilson, C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wild+sex+in+zebrafish:+loss+of+the+natural+sex+determinant+in+domesticated+strains.">Wild sex in zebrafish: loss of the natural sex determinant in domesticated strains.</a> Genetics. 198 (3), 1291-1308 (2014).</li><li>Liew, W. C., Orban, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zebrafish+sex:+a+complicated+affair.">Zebrafish sex: a complicated affair.</a> Genomics. 13 (2), 172-187 (2014).</li><li>Orban, L., Sreenivasan, R., Olsson, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long+and+winding+roads:+Testis+differentiation+in+zebrafish.">Long and winding roads: Testis differentiation in zebrafish.</a> Mol. Cell. Endocrinol. 312 (1-2), 35-41 (2009).</li><li>Blaser, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transition+from+non-motile+behaviour+to+directed+migration+during+early+PGC+development+in+zebrafish.">Transition from non-motile behaviour to directed migration during early PGC development in zebrafish.</a> J. Cell Sci. 118, 4027-4038 (2005).</li><li>Wang, X. G., Orban, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anti-M&#252;llerian+hormone+and+11+&#946;-hydroxylase+show+reciprocal+expression+to+that+of+aromatase+in+the+transforming+gonad+of+zebrafish+males.">Anti-M&#252;llerian hormone and 11 &#946;-hydroxylase show reciprocal expression to that of aromatase in the transforming gonad of zebrafish males.</a> Dev. Dynam. 236 (5), 1329-1338 (2007).</li><li>Siegfried, K. R., N&#252;sslein-Volhard, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Germ+line+control+of+female+sex+determination+in+zebrafish.">Germ line control of female sex determination in zebrafish.</a> Dev. Biol. 324 (2), 277-287 (2008).</li><li>Uchida, D., Yamashita, M., Kitano, T., Iguchi, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oocyte+apoptosis+during+the+transition+from+ovary-like+tissue+to+testes+during+sex+differentiation+of+juvenile+zebrafish.">Oocyte apoptosis during the transition from ovary-like tissue to testes during sex differentiation of juvenile zebrafish.</a> J. Exp. Biol. 205 (Pt 6), 711-718 (2002).</li><li>Groh, K. J., Sch&#246;nenberger, R., Eggen, R. I. L., Segner, H., Suter, M. J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+protein+expression+in+zebrafish+during+gonad+differentiation+by+targeted+proteomics.">Analysis of protein expression in zebrafish during gonad differentiation by targeted proteomics.</a> Gen. Comp. Endocr. 193, 210-220 (2013).</li><li>Siegfried, K. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+search+of+determinants:+gene+expression+during+gonadal+sex+differentiation.">In search of determinants: gene expression during gonadal sex differentiation.</a> J. Fish Biol. 76 (8), 1879-1902 (2010).</li><li>Small, C. M., Carney, G. E., Mo, Q., Vannucci, M., Jones, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+microarray+analysis+of+sex-+and+gonad-biased+gene+expression+in+the+zebrafish:+evidence+for+masculinization+of+the+transcriptome.">A microarray analysis of sex- and gonad-biased gene expression in the zebrafish: evidence for masculinization of the transcriptome.</a> BMC Genomics. 10, 579 (2009).</li><li>Chiang, E. F., Yan, Y. L., Guiguen, Y., Postlethwait, J., Chung, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two+Cyp19+(P450+aromatase)+genes+on+duplicated+zebrafish+chromosomes+are+expressed+in+ovary+or+brain.">Two Cyp19 (P450 aromatase) genes on duplicated zebrafish chromosomes are expressed in ovary or brain.</a> Mol. Biol. Evol. 18 (4), 542-550 (2001).</li><li>Kishida, M., Callard, G. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Distinct+cytochrome+P450+aromatase+isoforms+in+zebrafish+(Danio+rerio)+brain+and+ovary+are+differentially+programmed+and+estrogen+regulated+during+early+development.">Distinct cytochrome P450 aromatase isoforms in zebrafish (Danio rerio) brain and ovary are differentially programmed and estrogen regulated during early development.</a> Endocrinology. 142 (2), 740-750 (2001).</li><li>Rodr&#237;guez-Mar&#237;, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+and+expression+pattern+of+zebrafish+anti-M&#252;llerian+hormone+(amh)+relative+to+sox9a,+sox9b,+and+cyp19a1a,+during+gonad+development.">Characterization and expression pattern of zebrafish anti-M&#252;llerian hormone (amh) relative to sox9a, sox9b, and cyp19a1a, during gonad development.</a> Gene Expr.Patterns. 5 (5), 655-667 (2005).</li><li>Krovel, A. V., Olsen, L. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+of+a+vas::EGFP+transgene+in+primordial+germ+cells+of+the+zebrafish.">Expression of a vas::EGFP transgene in primordial germ cells of the zebrafish.</a> Mech Dev. 116 (1-2), 141-150 (2002).</li><li>Krovel, A. V., Olsen, L. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sexual+dimorphic+expression+pattern+of+a+splice+variant+of+zebrafish+vasa+during+gonadal+development.">Sexual dimorphic expression pattern of a splice variant of zebrafish vasa during gonadal development.</a> Dev. Biol. 271 (1), 190-197 (2004).</li><li>Tzung, K. W., 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=Early+depletion+of+primordial+germ+cells+in+zebrafish+promotes+testis+formation.">Early depletion of primordial germ cells in zebrafish promotes testis formation.</a> Stem Cell Reports. 4 (1), 61-73 (2015).</li><li>Hsiao, C., Tsai, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transgenic+zebrafish+with+fluorescent+germ+cell:+a+useful+tool+to+visualize+germ+cell+proliferation+and+juvenile+hermaphroditism+in+vivo.">Transgenic zebrafish with fluorescent germ cell: a useful tool to visualize germ cell proliferation and juvenile hermaphroditism in vivo.</a> Dev. Biol. 262 (2), 313-323 (2003).</li><li>Jorgensen, A., Nielsen, J. E., Morthorst, J. E., Bjerregaard, P., Leffers, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser+capture+microdissection+of+gonads+from+juvenile+zebrafish.">Laser capture microdissection of gonads from juvenile zebrafish.</a> Reprod Biol Endocrinol. 7, 97 (2009).</li><li>Chen, S., Zhang, H., Wang, F., Zhang, W., Peng, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=nr0b1+(DAX1)+mutation+in+zebrafish+causes+female-to-male+sex+reversal+through+abnormal+gonadal+proliferation+and+differentiation.">nr0b1 (DAX1) mutation in zebrafish causes female-to-male sex reversal through abnormal gonadal proliferation and differentiation.</a> Mol. Cell. Endocrinol. 433, 105-116 (2016).</li><li>Westerfield, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Zebrafish Book: A Guide for The Laboratory Use of Zebrafish (Danio rerio). , (2000).</li><li>Liew, W. C., 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=Polygenic+sex+determination+system+in+zebrafish.">Polygenic sex determination system in zebrafish.</a> PLoS One. 7 (4), e34397 (2012).</li><li>Parichy, D. M., Elizondo, M. R., Mills, M. G., Gordon, T. N., Engeszer, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Normal+table+of+postembryonic+zebrafish+development:+staging+by+externally+visible+anatomy+of+the+living+fish.">Normal table of postembryonic zebrafish development: staging by externally visible anatomy of the living fish.</a> Dev Dyn. 238 (12), 2975-3015 (2009).</li><li>Gupta, T., Mullins, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dissection+of+Organs+from+the+Adult+Zebrafish.">Dissection of Organs from the Adult Zebrafish.</a> J. Vis Exp. (37), (2010).</li><li>Arnaout, R., Reischauer, S., Stainier, D. Y. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recovery+of+Adult+Zebrafish+Hearts+for+High-throughput+Applications.">Recovery of Adult Zebrafish Hearts for High-throughput Applications.</a> J. Vis Exp. (94), (2014).</li><li>Gerlach, G. F., Schrader, L. N., Wingert, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dissection+of+the+Adult+Zebrafish+Kidney.">Dissection of the Adult Zebrafish Kidney.</a> J. Vis Exp. (54), (2011).</li><li>Yoon, C., Kawakami, K., Hopkins, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zebrafish+vasa+homologue+RNA+is+localized+to+the+cleavage+planes+of+2-+and+4-cell-stage+embryos+and+is+expressed+in+the+primordial+germ+cells.">Zebrafish vasa homologue RNA is localized to the cleavage planes of 2- and 4-cell-stage embryos and is expressed in the primordial germ cells.</a> Development. 124 (16), 3157-3165 (1997).</li><li>Braat, A. K., Speksnijder, J. E., Zivkovic, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Germ+line+development+in+fishes.">Germ line development in fishes.</a> Int. J. Dev. Biol. 43 (7), 745-760 (1999).</li><li>Huang, H. Y., Ketting, R. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+zebrafish+gonads+for+RNA+isolation.">Isolation of zebrafish gonads for RNA isolation.</a> Methods Mol Biol. 1093, 183-194 (2014).</li></ol>

The zebrafish has become a powerful model and is extensively used in development and disease-related research. The methods for isolation of organs in adult zebrafish such as brain, heart, gonad, and kidney, have been well documented23,24,25. Due to the small size and dynamic remodeling of the gonadal tissues in the larval zebrafish, isolation of gonadal tissue is a challenging task. Previous studies used whole dissected trunk ti...

The major female sex determinant in wild zebrafish chromosome 4 is lost or modified in the domesticated zebrafish (i.e. common lab strains)1. Instead, they have a polygenic sex determination system accompanied by environmental factors such as temperature, hypoxia, food availability and population density. The detailed mechanisms of zebrafish sex development are not fully understood. Fundamental questions such as when zebrafish sex determination occurs, what the primary sex determination signal(s) is/are, and which genes regulate the first step of gonad transformation remain to be answered2,3.
In the process of zebrafish sex development, several important stages have been recognized. In the early stage of development, starting from 4 hpf (hours post fertilization) primordial germ-cells (PGCs) undergo specification, migration to genital ridge and proliferation. PGC numbers and reciprocal interactions between germ cells and somatic cells are important for gonad differentiation4. At 13 dpf (days post fertilization), the gonads are in the undifferentiated stage. By 17 dpf, the gonads develop into bi-potential ovaries in both future females and males. The apoptosis-dependent transition from ovary to testis begin at 21 to 25 dpf and may continue for several weeks. By 35 dpf, the sex of the gonad has been determined and sex-specific gamete production is underway in both ovaries and testes5,6,7.
To date, diverse candidate genes and mechanisms of sex determination have been proposed. Proteomics and transcriptomic analysis have isolated many genes with sexually dimorphic expression and these genes have been utilized to study sex differentiation in zebrafish8,9,10. For example, in larval zebrafish, the cyp19a1a gene is specifically expressed in the ovary but not in the testis11,12. In addition, amh gene is weakly expressed in the ovarian follicle granulosa cells, but strongly in testis Sertoli cells13. In contrast, vasa gene is continuously expressed in the germ cells of both female and male zebrafish, making it a suitable gonad marker14,15.
Investigating gonadal gene expression levels is critical to understand the molecular mechanism of sex determination and differentiation especially in the bi-potential ovary stage3,9. However, the small size of larval zebrafish and correspondingly small gonads complicate the isolation of gonadal tissue for further molecular analysis. Previous studies used dissected whole trunk region between the opercula and anal pore16. This preparation, although containing gonads, consists of multiple tissues and organs. Alternatively, transgenic animals with gonad-specific GFP expression such as vasa: EGFP were used for gonadal tissue isolation via fluorescence activated cell sorting (FACS) and laser capture micro-dissection17,18. But their widespread application is limited. Here, we describe a simple procedure to isolate gonadal tissue from larval zebrafish at 17 dpf and 25 dpf. We demonstrate the position of the gonads with respect to other organs and isolate the morphologically intact gonads from the surrounding tissues. We further show the gonad-specific genes such as vasa and cyp19a1a are highly expressed in the isolated gonads compared with the trunk tissue through quantitative PCR (qPCR) analysis. The present protocol allows identification, isolation, RNA purification and amplification of gonadal specific genes from larval zebrafish, thereby enabling subsequent molecular analysis of gonadal tissue19.

<table border="0" cellpadding="0" cellspacing="0" width="975">
	<tbody>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Cell culture dish 100 mm</td>
			<td style="width:208px;">Corning</td>
			<td style="width:208px;">430167</td>
			<td style="width:351px;">For embryo incubation</td>
		</tr>
		<tr height="85">
			<td height="85" style="height:85px;width:208px;">20 X EM</td>
			<td style="width:208px;"></td>
			<td style="width:208px;"></td>
			<td style="width:351px;">For a 1 liter needed: add 17.5 g NaCl, 0.75 g KCl and 2.9 g CaCl.2H2O; then add 0.41 g KH2PO4, 0.412 g Na2HPO4 anhydrous and 4.9 g MgSO4. 7H2O.</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">1 X EM</td>
			<td style="width:208px;"></td>
			<td style="width:208px;"></td>
			<td style="width:351px;">Dilute 20 X EM in distilled water</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">AGAROSE G-10</td>
			<td style="width:208px;">Gene</td>
			<td style="width:208px;">121985</td>
			<td style="width:351px;">For preparing the 2% agar plates&#160;</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Trizol Reagent</td>
			<td style="width:208px;">Invitrogen</td>
			<td style="width:208px;">15596-026</td>
			<td style="width:351px;">For RNA isolation&#160;</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Meter glass</td>
			<td style="width:208px;">Shen Bo</td>
			<td style="width:208px;">250 ml</td>
			<td style="width:351px;">For preparing the 2% agar plates&#160;</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Microwave Oven</td>
			<td style="width:208px;">Midea</td>
			<td style="width:208px;">M1-211A</td>
			<td style="width:351px;">For heating the AGAR</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">TWEEZER DUMONT#5INOX</td>
			<td style="width:208px;">World Precision Instrument</td>
			<td style="width:208px;">500341</td>
			<td style="width:351px;">For dissection</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Stereomicroscope</td>
			<td style="width:208px;">Motic</td>
			<td style="width:208px;">SMZ168</td>
			<td style="width:351px;">For dissection</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Pure water equipment</td>
			<td style="width:208px;">Millipore</td>
			<td style="width:208px;"></td>
			<td style="width:351px;"></td>
		</tr>
		<tr height="81">
			<td height="81" style="height:81px;width:208px;">Ringer&#8217;s solution</td>
			<td style="width:208px;"></td>
			<td style="width:208px;"></td>
			<td style="width:351px;">For a 1 liter needed: Add 6.78g NaCl, 0.22 g KCl, 0.26 g CaCl2 and 1.19 g Hepes; then fill to 1 L; Adjust pH to 7.2. Sterilize by filtration and keep in an autoclaved clear polycarbonate container.</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Transfer pipette</td>
			<td style="width:208px;">Samco</td>
			<td style="width:208px;">202, 204</td>
			<td style="width:351px;"></td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Metal bath</td>
			<td style="width:208px;">QiLinbeier</td>
			<td style="width:208px;"></td>
			<td style="width:351px;">Model GL-150</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Microscope</td>
			<td style="width:208px;">Leica&#160;</td>
			<td style="width:208px;">M205 FA</td>
			<td style="width:351px;">For photomicrograph</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Centrifuge</td>
			<td style="width:208px;">Eppendorf</td>
			<td style="width:208px;">5417R</td>
			<td style="width:351px;"></td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Micro Scale RNA Isolation Kit&#160;</td>
			<td style="width:208px;">Ambion</td>
			<td style="width:208px;">AM1931</td>
			<td style="width:351px;">For RNA isolation from gonad tissues</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Dnase I&#160;</td>
			<td style="width:208px;">Sigma</td>
			<td style="width:208px;">AMPD1-1KT</td>
			<td style="width:351px;">For DNA digestion in the RNA solution&#160;</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">RevertAid First Strand cDNA Synthesis Kit</td>
			<td style="width:208px;">Thermo Scientific</td>
			<td style="width:208px;">#K1631</td>
			<td style="width:351px;">For&#160; first-strand cDNA synthesis</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Rnase H&#160;</td>
			<td style="width:208px;">Thermo Scientific</td>
			<td style="width:208px;">#EN0202</td>
			<td style="width:351px;">For digesting the residual RNA in the cDNA solution.</td>
		</tr>
		<tr height="98">
			<td height="98" style="height:98px;width:208px;">SYBR Green Realtime PCR Master Mix</td>
			<td style="width:208px;">TOYOBO</td>
			<td style="width:208px;">QPK-201</td>
			<td style="width:351px;">This product is a Taq DNA polymerase-based 2 x master mix for real-time PCR and&#160; applicable for intercalation assay with SYBR Green I.</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Spectrophotometer</td>
			<td style="width:208px;">Ne Drop</td>
			<td style="width:208px;">OD-2000+</td>
			<td>Measuring the concentration of the total RNA</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:208px;">Mastercycler</td>
			<td style="width:208px;">Eppendorf</td>
			<td style="width:208px;">AG 22331 Hamburg</td>
			<td>gene expression profiling</td>
		</tr>
	</tbody>
</table>

dissection of larval zebrafish gonadal tissue

Although wild zebrafish possess a ZZ/ZW sex-determination system, domesticated zebrafish have lost the sex chromosome. They utilize a polygenic sex determination system, where several genes distributed throughout the genome collectively determine the sex identities of individual fish. Currently, the genes involved in regulating gonad development and how they work remain elusive. Normally, isolating gonadal tissue is the first step to examine the sex developmental processes. Here, we present a procedure to isolate gonadal tissue from 17 dpf (days post fertilization) and 25 dpf zebrafish larvae. The isolated gonadal tissue may be subsequently examined by morphology and gene expression profiling.

Dissections of the gonads were performed on AB strain larval zebrafish. Figure 1 shows typical gonadal tissue of larval zebrafish at 17 dpf and 25 dpf. Firstly, the skin and muscles of one side of the abdomen is cut to expose the internal organs. After removing the mass of internal organs, the swim bladder together with the gonad remain in the trunk. The gonad was attached to the ventral side of swim bladder (arrow in Figure 1B<s...

Watch this Scientific Journal Video about Dissection of Larval Zebrafish Gonadal Tissue at JoVE.com

Dissection of Larval Zebrafish Gonadal Tissue

Here, we present a protocol for isolating gonadal tissue of larval zebrafish, which will facilitate investigations of zebrafish sex differentiation and maintenance.

Although wild zebrafish possess a ZZ/ZW sex-determination system, domesticated zebrafish have lost the sex chromosome. They utilize a polygenic sex ...

The overall goal of this procedure is to isolate gonadal tissue from larval zebrafish and analyze the molecular properties of the isolated tissue This method that can help answer key questions in the zebrafish's sex development field. Such as the conservation of genes in regulating gonad development and the molecular underpinnings of the zebrafish sex development. The main advantage of this technique is that gonadal tissues from zebrafish larvae as early as 17 days post fertilization can be dissected for cellular and the molecular biological status.Generally, individuals new to this method will struggle because of the small size and the dynamic remodel of the gonadal tissues in the larval zebrafish. To prepare for gondal disection, transfer two male and two female adult zebrafish to either side of a divided crossing tank. The following morning refresh the tank water and remove the barrier to initiate mating.One to two hours after fertilization collect and transfer about forty eggs into a 100 millimeter plate with 40 milliliters of embryo medium, or EM.Incubate the embryos at 28.5 degrees Celsius for four days, refreshing the EM twice per day. Following the incubation transfer the larvae to one liter tanks. After five days post-fertilization, or DPF, feed live rotifers to the fish.When the larvae reach ten DPF feed the fish live brine shrimp. Then, at 14 DPF, transfer the fish into a recirculating water system. Raise the larval zebra fish to 17 or 25 DPF.Then measure the body length of the larvae at 17 and 25 DPF. Prepare two percent agar plates for dissection by adding four grams of agar to 200 milliliters of sterile water. Heat the mixture in a microwave until it turns transparent.Cool the agar for 15 minutes, then pour it into 60 millimeter diameter petri dishes. Store the solidified agar plates at four degrees Celsius. To anesthetized 17 DPF larvae add crushed ice into the tank.Transfer the anesthetized larvae to a 100 millimeter chilled petri dish with 30 milliliters of cold Ringer's solution. Incubate the fish in the chilled Ringer's solution for at least 15 minutes to fully anesthetize the larvae. With a plastic spoon transfer the larvae to a pre-cooled agar plate.Submerge the entire fish body in ten milliliters of chilled Ringer's Solution and gently lay it on it's side. Under a stereomicroscope, at 25x magnification, use tweezers to clamp the fish trunk for stabilization. Then, with another pair of tweezers, rip the abdomen longitudinally from the anus to the heart.Next, gently remove the skin and muscles on one side of the body to expose the internal organs. Then, carefully remove the massive organs ventral to the swim blader. Avoid damaging the gonad attached to the swim bladder.Cut the connection between the swim bladder and interior body. Then, carefully pull out the entire swim bladder and the gonadal tissue. With tweezers, carefully separate the gondal tissue from the swim bladder.And clean up the surrounding adipose tissue. Immediately transfer the isolated gonadal tissue to a pre-chilled, 1.5 milliliters centrifuge tube, containing 200 microliters of Ringer's Solution. Keep the tube on ice until all gonadal tissues are separated from the larvae.To extract total RNA from larval gonadal tissue transfer the isolated gonads to a new RNase free 1.5 milliliter tube and remove the Ringer's Solution. Then, add 100 microliters of lysis solution. And vortex the tube until the tissue is completely lysed.After performing a total RNA extraction, according to the manufacturer's instructions, add one tenth the volume of DNase I buffer, and one microliter of DNase I to the RNA solution, and gently mix the contents of the tube. Incubate the sample at 37 degrees Celsius for 20 minutes. Next, add one tenth the volume of DNase inactivation reagent to the RNA solution.Incubate the sample at 70 degrees Celsius for ten minutes. Then, use a spectrophotometer to measure the concentration of the total RNA. To perform first strand cDNA synthesis use an oligo-dT linker primer and one to two micrograms of RNA to perform first strand cDNA synthesis, following the manufacturer's protocol.Incubate the reaction at 45 degrees Celsius for 90 minutes. Then, terminate the reaction by heating the sample at 70 degrees Celsius for five minutes. Add one microliter on RNase H to the cDNA solution to remove the residual RNA.Gently mix the contents of the tube and centerfuge the sample at approximately 13, 000 times G for ten seconds. Incubate the tube at 37 degrees Celsius for 20 minutes. Then, add 20 microliters of neucleous free water to the sample.And store the cDNA at negative 70 degrees Celsius. Finally, use fluorescent dye to perform QCPR using the condition and primers listed in the text protocol. This figure shows typical gonadal tissue of lavaral zebrafish at 17 DPF.The gonad is attached to the ventral side of the swim bladder, as seen here. At 17 DPF, the larvae contain the left and the right gonads, which are translucent. In most cases the gonads are surrounded by epithelial tissue and protonephridium.At 25 DPF, the gonad is often wrapped by adipose tissue, and big or small gonads may be observed. Finally, to analyze the molecular properties of the isolated gonadal tissue, expression levels of the gonadal markers amh, cyp19a1a, nanos3, and vasa were examined by QPCR. The results show significant increases in marker genes in gonad tissue compared to controlled tissue.Once mastered this technique can be done in an hour if it's performed properly. While attempting this procedure it's important to remember to provide consistent rearing conditions for larvae zebrafish, as it's critical to yield expected results. After it's development, this technique paved the way for researches in the field of sex development to explore sex determining mechanisms of zebra fish.After watching this video you should have a good understanding of how to isolate gonadal tissues from larval zebra fish.

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Research

JoVE Journal

Developmental Biology

10.0K visualizações.  Fudan University. The overall goal of this procedure is to isolate gonadal tissue from larval zebrafish and analyze the molecular properties of the isolated tissue This method that can help answer key questions in the zebrafish's sex development field. Such as the conservation of genes in regulating gonad development and the molecular underpinnings of the zebrafish sex development. The main advantage of this technique is that gonadal tissues from zebrafish larvae as early as 17 days post fertilization can be d...