The regulation of steady-state follistatin mRNA levels by different pituitary hormones and peptide factors was examined in granulosa cell cultures derived from diethylstilboestrol-treated immature rats. Cytosolic RNA from cell cultures was prepared by lysis and equal amounts of RNA from all samples were analysed with a solution—hybridization assay using a 32P-labelled antisense probe corresponding to a part of exon 5 together with a part of the 5′ end of exon 6 of the rat follistatin gene. In addition, a specific 35S-labelled probe for cyclophilin was used as an internal standard.
The results show that 5 μg FSH/1 for 24 to 72 h stimulated steady-state follistatin mRNA levels, reaching levels 18·5-fold higher than controls. LH (0·2-100 μg/l) had only minor effects on follistatin mRNA levels in FSH-primed granulosa cells and prolactin, GH and IGF-I did not show any significant effects. Activin raised basal as well as FSH-stimulated steady-state follistatin mRNA levels up to ten- and twofold above controls respectively, whereas epidermal growth factor was found to inhibit FSH-stimulated follistatin mRNA levels in a dose-dependent manner.
It is concluded that follistatin mRNA levels in granulosa cells are regulated by FSH rather than LH, and that the stimulation by FSH can be inhibited by epidermal growth factor but enhanced by activin. Activin alone was also capable of stimulating follistatin mRNA.