Histone H3 acetylation of StAR and decrease in DAX-1 is involved in the luteinization of bovine granulosa cells during in vitro culture.

We investigated the expression of genes and transcription factors associated with steroidogenesis during the luteinization of granulosa cells isolated from bovine small follicles. Granulosa cells produced progesterone when cultivated in a culture medium including serum and attached to the substrate and began to display an elongated or fibroblastic aspect within 24 h of culture. We observed an increase in the number of granulosa cells at the same time. P450arom expression in the cultured granulosa cells had decreased at 24 h compared with 0 h of culture, and afterward was maintained at a low level. This expression was consistent with the decline of E2 concentration in the medium. Expression of StAR and P450scc mRNAs in the cultured granulosa cells was significantly increased at 72 h compared with 0 h of culture. Although the expression of Ad4BP/SF-1 mRNA began to increase during period between 48 and 72 h of culture, protein expression of Ad4BP/SF-1 remained at a constant level throughout the culture period. DAX-1 mRNA expression had decreased at 24 h of culture and remained at a low level. In parallel with this expression, the protein expression of DAX-1 began to decrease between 24 and 48 h of culture and then remained at a low level. Histone H3 acetylation of the StAR promoter region was observed at 72 h of culture period. Our data suggested that the decrease of Dax-1 transcription factor and the increase in histone H3 acetylation may play important roles in progesterone synthesis in luteinizing granulosa cells.