Fig. 3. Maturation state of primordial follicles in WT and Foxl2^lacZ homozygous mutant ovaries. (A) Foxl2^lacZ expression determined by ß-galactosidase staining in newborn heterozygous and homozygous Foxl2^lacZ ovaries. ß-galactosidase staining is more intense in Foxl2^lacZ homozygous mutant ovaries than in Foxl2^lacZ heterozygous ovaries because of the two lacZ alleles present showing that there is no somatic cell loss in mutant ovaries. The inset section shows a representative primordial follicle from a double immunofluorescence staining of a mutant newborn ovary with anti-lacZ (green) and anti-GCNA (red) antibodies. LacZ expression was only detected in somatic cells but not in oocytes. (B) Hematoxylin and Eosin staining of P1 WT and mutant ovaries. Formation of primordial follicles was observed in WT and mutant ovaries (black arrowhead marking squamous granulosa cells; white arrowhead marking oocyte). (C) Immunofluorescence for Gcna1 (red) and MSY2 (green) on WT and mutant newborn ovaries. Gcna1 is expressed in germ cells until the pachytene stage of the prophase of Meiosis I, whereas MSY2 expression starts at the diplotene stage of Meiosis I. Comparison of WT and mutant neonatal ovaries shows no apparent difference in the expression profile of the two proteins, providing evidence that primordial follicles have progressed through the prophase of Meiosis I. Corresponding pictures are photographed at the same magnification.