Estrogen treatment up-regulates female genes but does not suppress all early testicular markers during rainbow trout male-to-female gonadal transdifferentiation

Abstract

In non-mammalian vertebrates, estrogens are key players in ovarian differentiation, but the mechanisms by which they act remain poorly understood. The present study on rainbow trout was designed to investigate whether estrogens trigger the female pathway by activating a group of early female genes (i.e. cyp19a1, foxl2a, foxl2b, fst, bmp4, and fshb) and by repressing early testicular markers (i.e. dmrt1, nr0b1, sox9a1 and sox9a2). Feminization was induced in genetically allmale populations using 17a-ethynylestradiol (EE2, 20 mg/kg of food during 2 months). The expression profiles of 100 candidate genes were obtained by real-time RT-PCR and 45 expression profiles displayed a significant differential expression between control populations (males and females) and EE2-treated populations. These expression profiles were grouped in five temporally correlated expression clusters. The estrogen treatment induced most of the early ovarian differentiation genes (foxl2a, foxl2b, fst, bmp4, and fshb) and in particular foxl2a, which was strongly and quickly up-regulated. Simultaneously, Leydig cell genes, involved in androgen synthesis, as well as some Sertoli cell markers (amh, sox9a2) were strongly repressed. However, in contrast to our initial hypothesis, some genes considered as essential for mammalian and fish testis differentiation were not suppressed during the early process of estrogen-induced feminization (dmrt1, nr0b1, sox9a1 and pax2a) and some were even strongly up-regulated (nr0b1, sox9a1and pax2a). In conclusion, estrogens trigger male-to-female transdifferentiation by up-regulating most ovarian specific genes and this up-regulation appears to be crucial for an effective feminization, but estrogens do not concomitantly down-regulate all the testicular differentiation markers.

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

“…Taken together, we speculate that in the three-spot wrasse, DMRT1 was up-regulated in the presence of AI, presumably due to changes in the proportion of germ cell types in the testis. Our data are consistent with a report showing that DMRT1 transcript was not suppressed during the early process of estrogen-induced feminization in rainbow trout (Vizziano-Cantonnet et al 2008). Therefore, DMRT1 transcription might not be regulated by steroid hormones.…”

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

“…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). These results together warrant a role for dmrt1 in testicular differentiation/spermatogenesis.…”

Exposure to Diethylstilbestrol During Embryonic and Larval Stages of Medaka Fish (Oryzias latipes) Leads to Sex Reversal in Genetic Males and Reduced Gonad Weight in Genetic Females

“…Probably, a negative feedback might have shut off the transcription of cyp19a1 to minimize the quantity of estrogens produced by the gonads because DES was already present. Earlier studies showed that treatment with E 2 and 17␣-ethynylestradiol to induce female sexual differentiation in European sea bass (5) and rainbow trout (30) resulted in reduced levels of cyp19a1 transcripts. Furthermore, studies using aromatase inhibitors for sex reversal in medaka (31,32) and other species (33) have also suggested a negative feedback relationship between estrogen levels and ovarian aromatase gene.…”