EXPRESSION OF THE OVINE STEM-CELL FACTOR GENE DURING FOLLICULOGENESISIN LATE FETAL AND ADULT OVARIES

Two ovine stem cell factor (oSCF) cDNAs (822 bp and 738 bp) were gener ated from ovarian follicle by RT-PCR. Nucleotide sequencing that the o SCF 822 bp cDNA encodes a precursor protein of 274 amino acids. An ami no acid change E-109 to (109)Q was the only sequence was the only sequ ence difference from that previously described for this species. The s maller (738 bp) oSCF cDNA was shown by nucleotide sequencing to be an mRNA splice variant, equivalent to that found in other mammals, in whi ch an exon (84 bp) encoding a potential proteolytic cleavage site is r emoved. Northern analysis revealed a single transcript of approximatel y 6.5 kb in follicles, corpora lutea and stroma of mid-luteal sheep ov aries. In situ hybridization was used to detect oSCF mRNA within ovari es of fetal sheep on days 90, 100, 120 and 135 of gestation (term=147) and of adult sheep within the breeding season. In fetal and adult ova ries, oSCF mRNA was detected in the granulosa cells of follicles at al l stages of follicle growth (primordial through to antral). The SCF ge ne was also expressed in granulosa cells of atretic follicles but appe ared to be down-regulated in the cumulus cells surrounding the oocyte at more advanced stages of atresia. Tn fetal ovaries at day 90 of gest ation (90DG), oSCF was expressed in the subepithelial mesenchymal cell s of the ovarian cortex. By 100DG the gene expression in the subepithe lial cells became restricted to a narrow region below the epithelium, and areas of expression were observed in groups isolated oocytes, prim ordial and primary follicles. oSCF gene expression also occurred in th e surface epithelial cells of 90DG ovaries, the expression was absent from these cells by 135DG and in adult ovaries. Localization of oSCF m RNA was observed in the ovarian rete and endothelial cells of blood ve ssels of fetal ovaries. These results suggest that oSCF may have an im portant and continuous role in the development and/or maintenance of g erm cells during follicle growth and atresia in sheep.