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. 2022 Sep 7;10:944776. doi: 10.3389/fcell.2022.944776

FIGURE 1.

FIGURE 1

Comparative ovarian morphogenesis in medaka, chicken, and rabbit. (A) In medaka, the gonadal primordium is composed of three cell populations: primordial germ cells (PGCs), ftz-f1+ cells, and sox9b+ supporting cell precursors. Sex determination is initiated just before hatching, at stage 38. sox9b+ cells surround PGCs to give rise to the germinal cradles that later form a multilayered germinal epithelium along with epithelial cells. At hatching, a basement membrane is formed at the ventral side. Meiosis is initiated 1-day post-hatching (dph), and foxl2 becomes expressed in supporting cells surrounding diplotene oocytes that exit cradles. Around 5 dph, cyp19a1+ becomes expressed in stroma cells in the ventral region. As follicles grow in the stroma, foxl2+ granulosa cells recruit cyp19a1a+ cells and cyp17a1+ theca cells. Ovarian cavity is formed around 30 dph. Adult ovaries still contain a germinal epithelium (inset) composed of undifferentiated sox9+ supporting cells, and germline stem cells that synchronously divide, enter meiosis and either die or exit the cradle to form follicles in the stroma. (B) In chickens, the gonadal primordium consists of two main compartments, the coelomic epithelium and the underlying mesenchyme. In the left ovary, the coelomic epithelium gives rise to the cortex and interstitial cells. FOXL2 +/CYP19A1 + pre-granulosa cells and CYP17A1+ steroidogenic cells derive from a PAX2+ mesenchymal population. Germ cells that migrate into the gonad from the bloodstream accumulate in the cortical region of the left ovary. The right ovary does not form a cortex and germ cells remain in the medulla. (C) In rabbits, ovarian cell differentiation starts at 18 dpc and is associated with an upregulation of FOXL2, WNT4 and RSPO1 in somatic cells. At this stage, proliferating cells in the coelomic epithelium start to express CYP19A1. At 30 dpc, somatic cells expressing FOXL2, WNT4 and RSPO1 surround OCT4/STRA8 positive germ cells and form ovigerous cords. The expression of STRA8 signals meiosis initiation. At 14 dpp, the formation of the first primordial follicles is initiated. Then, growing follicles are composed of FOXL2+ granulosa cells enclosing VASA+ oocytes.