Sexual Dimorphic Expression of Genes in Gonads During Early Differentiation of a Teleost Fish, the Nile Tilapia Oreochromis niloticus1

Abstract

The Nile tilapia, a gonochoristic teleost fish with an XX/XY sex-determining system, provides an excellent model for studying gonadal sex differentiation because genetic all-females and all-males are available. In this study, we used quantitative real-time RT-PCR to determine the precise timing of the gonadal expression of 17 genes thought to be associated with gonadal sex differentiation in vertebrates. Gonads were isolated from all-female and all-male tilapia before (5-15 days after hatching [dah]) and after (25-70 dah) morphological sex differentiation. The transcript of aromatase (cyp19a1a), an enzyme responsible for producing estradiol-17beta, was expressed only in XX gonads at 5 dah, with a marked elevation in expression thereafter. In contrast, mRNA expression of steroid 11beta-hydroxylase (cyp11b2), an enzyme responsible for the synthesis of 11-ketotestosterone (11-KT, a potent androgen in fish), was found in XY gonads from 35 dah only. These results, combined with the presence of transcripts for other steroidogenic enzymes and estrogen receptors in XX gonads at 5-7 dah, are consistent with our earlier suggestion that estradiol-17beta plays a critical role in ovarian differentiation in tilapia, whereas a role for 11-KT in testicular differentiation is questionable. A close relationship between the expression of foxl2, but not nr5a1 (Ad4BP/SF-1), and that of cyp19a1a in XX gonads suggests an important role for Foxl2 in the transcriptional regulation of cyp19a1a. Dmrt1 exhibited a male-specific expression in XY gonads from 6 dah onward, suggesting an important role for Dmrt1 in testicular differentiation. Sox9 and amh (anti-Mullerian hormone) showed a testis-specific expression, being evident only in the later stages of testicular differentiation. It is concluded that the sex-specific expression of foxl2 and cyp19a1a in XX gonads and dmrt1 in XY gonads during early gonadal differentiation (5-6 dah) is critical for undifferentiated gonads to differentiate into either the ovary or testis in the Nile tilapia.

Identification of multiple dmrt1s in catfish: localization, dimorphic expression pattern, changes during testicular cycle and after methyltestosterone treatment

“…Multiple forms of dmrt1 exist in developing testis but not in developing ovary of catfish. Male-specific expression of Dmrt1 was noticed in some species like human (Moniot et al 2000), chicken (Nanda et al 1999), frog (Osawa et al 2005), garden lizard (Sreenivasulu et al 2002) and some fish species (Fernandino et al 2006, Ijiri et al 2008, Xia et al 2007. In our study, we observed male-specific expression of multiple dmrt1s in developing and adult catfish.…”

“…On the contrary, dimorphic expression pattern of male and female sexspecific genes were observed in completely developed testis and ovary. Such dimorphic expression pattern was also reported during gonadal sex differentiation and/ or hormone-induced sex reversal (Alam et al 2008, Ijiri et al 2008. By contrast, in rainbow trout oestrogen treatment up-regulates female specific genes but does not suppress all male specific genes during male-to-female gonadal trans-differentiation (Vizziano-Cantonnet et al 2008).…”

Histological observation of doublesex-mab 3-related transcription factor 1 (DMRT1) localization in the adult testis of three-spot wrasse

“…DMRT1 has been cloned in several vertebrates and its involvement in testicular differentiation was investigated extensively (Ferguson-Smith 2007;Ijiri et al 2008;Raymond et al 2000). However, the precise role of DMRT1 during spermatogenesis remains largely unknown.…”

Effects of sexual steroids on the expression of foxl2 in Gobiocypris rarus

“…A very close relation between foxl2 and cyp19a1a in tilapia showed the important roles of Foxl2 in regulating cyp191a and ovarian development (Ijiri et al, 2008). Fish including G. rarus have two aromatases, one is the ovarian type and one is the brain type encoded by cyp19a1a and cyp19a1b, respectively (Cao et al, unpublished;Wang et al, 2010).…”