Establishment of a stem Leydig cell line capable of 11-ketotestosterone production

The cellular expression patterns of gdnfa and gdnfb in the gonads of Nile tilapia and their differential response to retinoic acid

In mammals, glial cell derived neurotrophic factor (GDNF) plays a critical role in the self-renewal and maintenance of spermatogonial stem cells (SSCs) in testis and oogenesis in ovary, whilst retinoic acid (RA), the key factor of meiosis initiation, can downregulate its expression. Unlike mammals, two Gdnf replication genes are widely present in teleost fishes, however, our understanding of them is still poor. In the present study, two paralogous gdnf from Nile tilapia (Oreochromis niloticus), namely as Ongdnfa and Ongdnfb, were characterized, and then their cellular expression profiles in testis and ovary and responsiveness to RA treatment at the tissue and cellular levels were investigated. In phylogenetic tree, the Gdnfa and Gdnfb from teleost fishes were clustered into two different subclasses, respectively, and then clustered with the homologs from cartilaginous fish and tetrapods, suggesting that OnGdnfa and OnGdnfb are orthologous to GDNF and paralogous to each other. Ongdnfa is expressed in Sertoli cells and Leydig cells in testis and oocytes in ovary. The expression pattern of Ongdnfb is similar to Ongdnfa. In the ex vivo testicular organ culture, RA down-regulated the expression of Ongdnfa, whereas up-regulated the expression of Ongdnfb (P < 0.05), suggesting that they have differential responsiveness to RA signaling. RA treatment of the cultured cells derived from adult Nile tilapia testis which have the expression of RA receptors (RAR), Ongdnfa and Ongdnfb further confirmed the above result. Collectively, our study suggests that Ongdnfa and Ongdnfb have non-germline expression patterns in testis and germline expression patterns in ovary; furthermore, they have differential responsiveness to RA signaling, implying that they might have differential biological functions. This study broadens and enriches our understanding of fish GDNF homologs and lays foundation for the study of their biological functions in the future.

Characterization of nanog in Nile tilapia (Oreochromis niloticus) and its spatiotemporal expression patterns during embryonic and gonadal development

Nanog is one of the well-characterized core transcription factors in pluripotency maintenance network. So far, studies on fishes indicate that the Nanog expression occurs from embryonic 1-cell stage to blastula stage, and is restricted to the gonadal germline cells in adult tissues, which is strikingly different from that in mammals. However, whether this expression profile is conservative in fishes remains to be investigated. Here Nile tilapia (Oreochromis niloticus) nanog (named as Ong) was identified and its spatiotemporal expression patterns during embryonic and gonadal development were investigated. The Ong cDNA contains an open reading frame of 678 bp, encoding 226 amino acids. The anti-Ong antibody was prepared through prokaryotic protein expression and its specificity was validated. The Ong expression in embryonic 1-cell stage did not appear until the early stage of blastocyst and continued to the late stage of blastocyst. In adult tissues, its expression was limited to gonads. Its expression patterns during gonadal development were further investigated by in situ hybridization and immunohistochemical staining. In testis, Ong was not expressed at 30 dah (days after hatching), but highly expressed in spermatogonia and spermatocytes at 150 dah; in ovaries at 30 and 150 dah, it was not expressed in germline cells but in all somatic cells. This expression profile is strikingly different from reports in fishes to date. Our study firstly indicates that the Nanog expression profile is not conservative in fishes. This study is valuable for further functional and evolutionary study of this gene.

Germline sexual fate is determined by the antagonistic action of dmrt1 and foxl3/foxl2 in tilapia

Germline sexual fate has long been believed to be determined by the somatic environment, but this idea is challenged by recent studies of foxl3 mutants in medaka. Here, we demonstrate that the sexual fate of tilapia germline is determined by the antagonistic interaction of dmrt1 and foxl3, which are transcriptionally repressed in male and female germ cells, respectively. Loss of dmrt1 rescued the germ cell sex reversal in foxl3Δ7/Δ7 XX fish, and loss of foxl3 partially rescued germ cell sex reversal but not somatic cell fate in dmrt1Δ5/Δ5 XY fish. Interestingly, germ cells lost sexual plasticity in dmrt1Δ5/Δ5 XY and foxl3Δ7/Δ7 XX single mutants, as aromatase inhibitor (AI) and estrogen treatment failed to rescue the respective phenotypes. However, recovery of germ cell sexual plasticity was observed in dmrt1/foxl3 double mutants. Importantly, mutation of somatic cell-specific foxl2 resulted in testicular development in foxl3Δ7/Δ7 or dmrt1Δ5/Δ5 mutants. Our findings demonstrate that sexual plasticity of germ cells relies on the presence of both dmrt1 and foxl3. The existence of dmrt1 and foxl3 allows environmental factors to influence the sex fate decision in vertebrates.