RESUMO
SOX9 is expressed at the onset of the genital ridge formation in both sexes. It is assumed that SRY, the testis determining gene, turns SOX9 on in male embryos because it is turned off in female embryos. Spatial expression of SRY follows a cranio-caudal pattern. Here, we asked if SOX9 is expressed in the same cell lineage and with a similar pattern as SRY. A correlative study between the structural changes in the genital ridge and the immunocytochemical localization of SOX9-positive cells was undertaken. We used a transgenic strain expressing the green fluorescent protein (GFP) that considerably enhanced the cell context where the first SOX9-positive cells appear. Although SOX9-positive cells are located among loose mesenchymal cells by stages of 8-14 tail somites (ts) in both sexes, they are absent in the thickening coelomic epithelium of females. At 15 ts the first SOX9-positive cells appear within the core of the condensed cells only in male genital ridges. At 17 ts, a gradient of SOX9-positive cells in males is apparent, closely following the cranio-caudal pattern of cell aggregation seen in genital ridges of both sexes. Hence, our results suggest that SOX9 is expressed only in loose mesenchymal cells in both sexes and that expression of SOX9 in males requires the prior aggregation of cells in the genital ridges. The correspondence of SOX9 and SRY pattern of expression supports that both genes are expressed in the preSertoli cell lineage in the core of the genital ridges.
Assuntos
Genitália/citologia , Proteínas de Grupo de Alta Mobilidade/metabolismo , Células de Sertoli/citologia , Células-Tronco/metabolismo , Fatores de Transcrição/metabolismo , Animais , Agregação Celular , Linhagem da Célula , Feminino , Genitália/embriologia , Genitália/metabolismo , Proteínas de Fluorescência Verde , Proteínas Luminescentes/análise , Proteínas Luminescentes/genética , Masculino , Camundongos , Camundongos Transgênicos , Fatores de Transcrição SOX9 , Células-Tronco/citologia , Células-Tronco/fisiologiaRESUMO
Although sex determination starts in the gonads, this may not be the case for species with temperature sex determination (TSD). Since temperature affects the whole embryo, extragonadal thermosensitive cells may produce factors that induce gonadal sex determination as a secondary event. To establish if gonads of a species with TSD respond directly to temperature, pairs of gonads were cultured, one at female-promoting temperature (FPT) and the contralateral at male-promoting temperature (MPT). Histological and immunohistochemical detection of SOX9 revealed that the response to temperature of isolated gonads was similar to that of the gonads of whole embryos. While gonads cultured at MPT maintained SOX9 expression, it was downregulated in gonads at FPT. Downregulation of SOX9 took longer in gonads cultured at stage 23 than in gonads cultured at stage 24, suggesting that a developmental clock was already established at the onset of culture. To find out if sex commitment occurs in vitro, gonads were switched from FPT to MPT at different days. Results showed that the ovarian pathway was established after 4 days of culture. The present demonstration that gonads have an autonomous temperature detector that regulates SOX9 expression provides a useful starting point from which the molecular pathways underlying TSD can be elucidated.