Mutations in the forkhead transcription factor gene FOXL2 are involved in ovarian failure, which occurs in human BPES syndrome. This syndrome presents a sexually dimorphic expression, specific to the ovary in several vertebrates. We cloned the open reading frame of chicken FOXL2 (cFoxL2) and studied cFoxL2 expression in developing gonads and during adulthood to examine the role of FOXL2 in ovarian differentiation and function in birds. The spatial and temporal dynamics of cFoxL2 and aromatase expression were analyzed in parallel by using real-time quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry in attempt to investigate the possible role of cFoxL2 in the regulation of aromatase. The expression patterns of cFoxL2 and aromatase transcripts were highly correlated during the sex-differentiation period (4.7-12.7 days of incubation). Aromatase and cFoxL2 proteins were colocalized in the medullar part of female gonads on embryonic day 14. Fourteen days after hatching, cFoxL2 protein was mainly detected in granulosa cells of developing follicles. In adult ovary follicular envelopes, apart from granulosa cells, cFoxL2 transcript and protein were detected at lower levels in theca cells where aromatase was present. A high level of cFoxL2 transcription was also observed in maturing and ovulated oocytes. Our results confirm that FoxL2 is an early regulator of ovarian development in birds and may be involved in aromatase transcription regulation. Developmental Dynamics 231:859 -870, 2004.
In the tilapia Oreochromis niloticus, sex is determined genetically (GSD), by temperature (TSD) or by temperature/genotype interactions. Functional masculinization can be achieved by applying high rearing temperatures during a critical period of sex differentiation. Estrogens play an important role in female differentiation of non-mammalian vertebrates. The involvement of aromatase, was assessed during the natural (genetic all-females and all-males at 27 degrees C) and temperature-induced sex differentiation of tilapia (genetic all-females at 35 degrees C). Gonads were dissected between 486--702 degree x days. Aromatase gene expression was analyzed by virtual northern and semi-quantitative RT-PCR revealing a strong expression during normal ovarian differentiation concomitant with high levels (465 +/- 137 fg/g) of oestradiol-17 beta (E2-17 beta). This was encountered in gonads after the onset of ovarian differentiation (proliferation of both stromal and germ cells prior to ovarian meiosis). Genetic males exhibited lower levels of aromatase gene expression and E2-17 beta quantities (71 +/- 23 fg/ g). Aromatase enzyme activity in fry heads established a sexual dimorphism in the brain, with high activity in females (377.9 pmol/head/hr) and low activity in males (221.53 pmol/head/hr). Temperature induced the masculinization of genetic females to a different degree in each progeny, but in all cases repression of aromatase expression was encountered. Genetic males at 35 degrees C also exhibited a repression of aromatase expression. Aromatase brain activity decreased by nearly three-fold in the temperature-masculinized females with also a reduction observed in genetic males at 35 degrees C. This suggests that aromatase repression is required in the gonad (and perhaps in the brain) in order to drive differentiation towards testis development. Mol. Reprod. Dev. 59:265-276, 2001.
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