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Kenngott, Rebecca Anna-Maria; Vermehren, M.; Ebach, Katja; Sinowatz, Fred (2013): The Role of Ovarian Surface Epithelium in Folliculogenesis during Fetal Development of the Bovine Ovary: A Histological and Immunohistochemical Study. In: Sexual Development, Nr. 4: S. 180-195
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Abstract

Although many aspects of ovarian differentiation have been established,comparatively little is known about prenatal follicle formation anddifferentiation of bovine ovaries. The objective of this investigationwas to study the role of the surface epithelium during the developmentof germ cell nests, germ cell cords and follicle formation in the fetalbovine ovary. Associated important proliferation and apoptotic featureswere further investigated. Additionally, the expression pattern of theS100 protein was detected. A strong increase of mitotic figures wasdetected in the surface epithelium, germ cell nests and germ cell cordsof ovaries with a crown-rump length (CRL) of 13.0-58.0 cm. Oocytes werepositively stained with S100 in bovine ovaries from fetuses with a CRLof 21.0 cm. The staining intensity enhanced parallel to increasingoocyte and follicle sizes during the ovary development. In later stages,a strong staining for S100 was observed in healthy oocytes incontradistinction to atretic oocytes where no expression of the S100protein could be found. In conclusion, increasing mitosis index ofsurface epithelium cells, as well as oogonia directly beneath thesurface epithelium, in combination with open surface connection duringstages from a CRL of 11.0-94.0 cm of bovine fetal ovaries could play animportant role in the period of time of ongoing folliculogenesis andderivation of granulosa cells. Additionally, S100-positive oocytes inprimordial and later follicle stages joined by a high rate ofKi67-positive index in surrounding granulosa cells indicate that in theoocytes the S100 protein can perhaps be a useful marker for intactoocytes in bovine ovaries.