Figure 4. Involvement of Inhbb in germ cell loss in the absence of Wnt4.

(A–C) Whole mount in situ hybridization for Inhbb was performed on control ovary (SF1/cre;Ctnnb^f/+ or Ctnnb1^f/−) (A), β-catenin cKO ovary (SF1/cre;Ctnnb^f/−) (B), and Wnt4^−/−;SF1/cre; Ctnnb1^fl.(ex3) ovary (C) at 13.5 dpc. (n = 2–3 for each genotypes). o =  ovary, m =  mesonephros. (D–F) Immunohistochemistry for TRA98 (red) and CYP17 (green) was performed on ovary sections from control (Wnt4^+/−; Inhbb^+/−), Wnt4 single KO and Wnt4; Inhbb double KO ovary at birth. (G) Light field microscopic images of the reproductive tract were taken from control female, Wnt4 single KO, and Wnt4; Inhbb double KO females at birth. Arrowheads indicate oviduct and arrows indicate epididymal structure. o = ovary. (J–L) Immunohistochemistry for TRA98 (red) and SCP3 (green) were performed on ovary sections from control, Wnt4 single KO and Wnt4; Inhbb double KO ovary at 15.5 dpc. At this stage, the female germ cells have not lost yet in the Wnt4 KO ovaries, allowing us to monitor the status of meiosis. The insets are the images of a higher magnification of cells double-positive (yellow) for TRA98 and SCP3. Scale bar represent 250 µm in A–C, G–I and 100 µm in D–F, J–L. (M) A proposed model for the somatic cell-derived pathway on female germ cell survival: In the mouse fetal ovary, WNT4 signals via β-catenin to decrease the expression of activin βB or Inhbb, which causes loss of meiotic germ cell. WNT4 also stimulates the production of follistatin (Fst), which acts to antagonize the activity of Inhbb. The WNT4/β-catenin pathway also prevents the ectopic production of androgens in the fetal ovary, which is not responsible for the germ cell loss. WNT4 could possibly regulate its own expression via β-catenin.