Restricted expression of WT1 messenger ribonucleic acid in immature ovarian follicles: Uniformity in mammalian and avian species and maintenance during reproductive senescence

WT1 is a zinc finger protein with transcriptional repressor activity on sev eral growth factor and growth factor receptor genes. In the ovary, a potent ial role for WT1 in the suppression of the development of immature follicle s has been demonstrated, Here, gel retardation assays further showed that r ecombinant WT1 protein interacted with consensus DNA sequences in the inhib in-alpha gene promoter. We investigated the pattern of WT1 expression in a wide variety of species and also over the reproductive life span in rats. I n chicken ovaries, Northern blot analysis revealed the presence of WT1 tran script in small healthy white follicles (1-5 mm in diameter) and its absenc e in small yellow (6-12 mm in diameter) or larger follicles (F-1-F-5). In p ig and monkey ovaries, WT1 expression was limited to granulosa cells of pre antral follicles, as shown by in situ hybridization analysis. In rats, Nort hern blot analyses demonstrated the presence of WT1 transcript in the ovari es of young (3-mo-old) and middle-aged (9-mo old) rats on the proestrous da y, with a decrease in old (12-mo-old) rats in persistent estrus. In situ hy bridization analysis further suggested that the decrease in WT1 expression in aging ovaries was associated with fewer immature follicles. Thus, WT1 ex pression is restricted to immature follicles in diverse avian and mammalian species and over the reproductive life span in rats, These data demonstrat ed that WT1 is a marker for immature follicles and suggested a potential ro le of this transcriptional repressor in the slow growth of early follicles.