Temperature regulates SOX9 expression in cultured gonads of Lepidochelys olivacea, a species with temperature sex determination

Although sex determination starts in the gonads, this may not be the case f or species with temperature sex determination (TSD). Since temperature affe cts the whole embryo, extragonadal thermosensitive cells may produce factor s that induce gonadal sex determination as a secondary event. To establish if gonads of a species with TSD respond directly to temperature, pairs of g onads were cultured, one at female-promoting temperature (FPT) and the cont ralateral at male-promoting temperature (MPT). Histological and immunohisto chemical detection of SOX9 revealed that the response to temperature of iso lated gonads was similar to that of the gonads of whole embryos. While gona ds cultured at MPT maintained SOX9 expression, it was downregulated in gona ds at FPT. Downregulation of SOX9 took longer in gonads cultured at stage 2 3 than in gonads cultured at stage 24, suggesting that a developmental cloc k was already established at the onset of culture. To find out if sex commi tment occurs in vitro, gonads were switched from FPT to MPT at different da ys. Results showed that the ovarian pathway was established after 4 days of culture. The present demonstration that gonads have an autonomous temperat ure detector that regulates SOX9 expression provides a useful starting poin t from which the molecular pathways underlying TSD can be elucidated. (C) 2 001 Academic Press.