Fig. 6.
A brief period of Dazl expression is sufficient for germ cell commitment, and for completion of oogenesis. (A) Time course of Ddx4-Cre (MvhCre-mOrange) recombinase activity in embryonic germline using a fluorescent Cre reporter mouse line, LSL-tdTomato. Cre-mediated recombination (resulting in tdTomato expression) in Oct4:EGFP-positive cells is assayed by flow cytometry. Numbers of embryos tested are listed in each column, mean + SD. (B) Breeding scheme for Dazl conditional knockout (Dazl cKO) mice. (C) Histology of control (Upper) and B6.Dazl cKO ovary (Lower) stained with PAS at 20 d of age, with primary (arrow head) and secondary (chevron) follicles marked. (D) Immunofluorescence of control (Upper) and B6.Dazl cKO testis (Lower) at 8 mo of age. Germ cells are immunostained by GCNA (blue), and undifferentiated spermatogonia are immunostained by GFP (green) expressed from the Oct4:EGFP reporter. Cre recombination is confirmed by immunostaining for DAZL (red). DNA is stained with DAPI (gray). Insets show each marker in Oct4:EGFP-positive spermatogonia (arrow head); * denotes tubule with incomplete Dazl recombination in cKO testis. (E) Immunofluorescence of control (Upper) and B6.Dazl cKO ovary (Lower) at postnatal day 1. Germ cells are immunostained by tdTomato protein (expressed following recombination of tdTomato-LSL allele by Ddx4-Cre; blue). Cre recombination is confirmed by immunostaining for DAZL (red). DNA is stained with DAPI (gray). (F) B6.Dazl cKO females remained fertile for at least 8 mo. (G) B6.Dazl cKO males were sterile, with no spermatozoa in epididymal ducts. All data are mean + SD. (Scale bars, 50 µm.)