Inactivation of Wt1 causes pre-granulosa cell to steroidogenic cell transformation and defect of ovary development†

Wt1 gene encodes a nuclear transcription factor which is specifically expressed in ovarian granulosa cells and testicular Sertoli cells. Our previous studies demonstrated that Wt1 is required for the lineage specification of supporting cells and inactivation of Wt1 results in Sertoli cells to Leydig-like cells transformation. To test whether Wt1 is also involved in lineage maintenance of granulosa cells during ovary development, Wt1 was specifically deleted in pre-granulosa cells using Foxl2-cre. We found that the female Wt1-/flox; Foxl2-cre mice were infertile with atrophic ovaries and no growing follicles with multiple layers of granulosa cells were observed. A large number of 3β-HSD-positive steroidogenic cells were detected in ovaries of Wt1-/flox; Foxl2-cre mice during embryonic stage and these cells were derived from Foxl2-expressing pre-granulosa cells. The quantitative results showed the expression of granulosa cell marker genes (Foxl2, Follistatin) was downregulated and steroidogenic cell marker genes (3β-HSD, Cyp11a1, Star and Sf1) was dramatically increased in Wt1-/flox; Foxl2-cre ovaries. We also found that the meiosis of germ cells in Wt1-/flox; Foxl2-cre ovaries was delayed but not arrested. This study demonstrates that Wt1 is required for lineage maintenance of granulosa cells and inactivation of Wt1 results in pre-granulosa cells to steroidogenic cells transformation which in turn causes the defect of ovary development.