The promoter for the ovine follicle-stimulating hormone-beta gene (FSHbeta) confers FSHbeta-like expression on luciferase in transgenic mice: regulatory studies in vivo and in vitro

Transgenic mice harboring the ovine FSHbeta (oFSHbeta) promoter plus first intron (from -4741 to +759 bp) linked to a luciferase reporter gene (oFSHbetaLuc) were generated to determine whether this promoter can direct tissue-specific expression in vivo and serve as a model for studying hormonal regulation of the FSHbeta gene. Of six lines of transgenic mice analyzed, luciferase was detected uniquely in the pituitaries of five of them. Pituitary luciferase activity was decreased 51-99% by chronic GnRH treatment (Lupron depot). Orchidectomy caused a 2- to 8-fold increase, and ovariectomy caused a 2- to 27-fold increase in pituitary luciferase activity. Furthermore, pituitary luciferase expression was consistently higher on estrus than on diestrus (3- to 20-fold). These data strongly suggested that the transgene was expressed specifically in pituitary gonadotropes and regulated in the same way as the endogenous mouse FSHbeta gene. Using primary pituitary cell cultures prepared from these transgenic mice, basal luciferase expression was maximal on day 3 and then decreased by day 6 of culture, a pattern reflected by endogenous mouse FSH secretion. In these pituitary cultures, basal oFSHbetaLuc expression was decreased 61-82% by follistatin or 59-79% by inhibin. Similarly, mouse FSH secretion was decreased 71% by follistatin or 65% by inhibin. Progesterone inhibited oFSHbetaLuc expression by 44-51%, but it had no effect on endogenous mouse FSH secretion. Estradiol lowered FSH secretion by 21%, but did not decrease oFSHbetaLuc expression significantly. In conclusion, these data demonstrated the ability of the oFSHbeta promoter to direct expression of a reporter gene specifically to pituitary gonadotropes in transgenic mice. Studying oFSHbetaLuc expression in vivo and in cell cultures derived from pituitaries of these transgenic mice should prove useful for understanding many features of FSHbeta regulation.