Formação do epitelio germinativo durante a morfogenese e diferenciação gonodal em Cyprinus carpio (Teleostei:Cypriniformes) : analise estrutural e ultraestrutural das celulas germinativas e somaticas / Formation of germinal epithelium during gonodal morphogenesis and differentiation in Cyprinus carpio (Teleostei:Cypriniformes) : a structural and ultrastructural analysis of the germ and somatic cells

Talita Sarah Mazzoni

The description of gonadal morphogenesis in Cyprinus carpio provides a new vision of proliferation and differentiation of germ and somatic cells from the gonadal primordium leading to the formation of different ovarian and testicular structures, and the constitution of germinal epithelium which borders the ovigerous lamellae and the seminiferous tubules. In C. carpio the gonadal primordium is an elongated structure with individual PGCs scattered among somatic cells. The PGCs divide and organize into continuous cords that are delimited by the somatic cells. Then, in female gonad, somatic cells move into the cords, wrap around and individualize the PGCs that subsequently differentiate in oogonia. Each oogonium is wrapped by the now prefollicle cells giving rise to a cyst. Prefollicle cells rest upon a forming basement membrane. Inside the cysts oogonium proliferates by mitosis, originating new oogonia. Or, they enter into meiosis, becoming oocytes. Oocytes advance to diplotene where meiosis is arrested. Still inside the cysts oocytes enter primary growth, they are subsequently surrounded by prefollicle cells, and they become ovarian follicles. The differentiating gonad maintains a compact structure, continues elongating and becomes larger. Invaginations appear in the ventral region of the ovary; these form the ovigerous lamellae. Mesenchymal cells scattered inside the lamellae move away from one another giving rise to the extra-vascular space in the developing stroma where the cellular processes of these cells connect to one another and form a cellular net. Meanwhile, epithelial cells coming from the gonad periphery, and present in the ventral invaginations, associate with oogonia forming germinal epithelium. These also interact with the follicles that become connected to the epithelium sharing some extension of the basement membrane. Mesenchymal cells surround the ovarian follicles, becoming theca and, include the follicle, forms the follicle complex. On either side of the developing ovary, a coelomic epithelial cell proliferation forms a laminar tissue that grows ventrally, then extending beneath the developing ovary and fusing to form the central lumen of the carp cystovarian ovary. In male gonad, somatic cells move into the cords, wrap around and individualize the PGCs that subsequently differentiate in spermagonia. Each spermatogonium wrapped by the now pre-Sertoli cells giving rise to a cyst. The cysts join one another forming clusters. A basement membrane is synthesized around each cluster. Pre-Sertoli cells rest upon the forming basement membrane. In the center of the clusters a space is created when pre-Sertoli cells move away from one another. Then, nearby clusters fuse to one another that become connected by the same luminal space. The progressive fusion of the clusters gives rise to the seminiferous tubules that are bordered by the new formed germinal epithelium constituted by the cysts that rest upon the basement membrane. Mesenchymal cells surround the seminiferous tubules give rise to the cellular components of the interstitial compartment. Inside the cysts spermatogenesis starts. As the final spermatic cells are released into the luminal compartment, the anostomosis of the testicular tubules occurs forming the spermatic duct on the dorsal region of the testis.

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