Evidence for regulation of basic fibroblast growth factor gene expression by photoperiod and melatonin in the ovine pars tuberalis

Abstract

In the ovine pituitary the in vivo expression of the bFGF gene was studied using in situ hybridisation and Northern analysis. Expression of bFGF mRNA was highest in the pars tuberalis (PT) and zona tuberalis (ZT) and this expression was higher in the pituitaries of animals acclimited to long days than in those from short day housed animals. Expression in the pars intermedia (PI) was also detectable but the pars distalis (PD) showed negligible expression compared with the PT. Regulation of bFGF gene was investigated in primary cultured PT cells. Both forskolin and PMA increased bFGF mRNA expression significantly and melatonin was able to inhibit these effects partially, however there was no independent effect of melatonin on bFGF mRNA levels. Despite the inducibility of the bFGF gene, bFGF protein levels in PT culture media were insensitive to the same stimuli and detectable bFGF protein declined with time. Exogenous bFGF had no effect on c-fos mRNA levels and did not increase prolactin secretion from ovine lactotrophs. In contrast c-fos mRNA was induced in GH3 cells by bFGF. These data suggest that although basic fibroblast growth factor (bFGF) mRNA expression in the ovine PT is photoperiodically-sensitive, it is not directly involved in the seasonal regulation of lactotrophic activity.