The Role of Ovarian Surface Epithelium in Folliculogenesis during Fetal Development of the Bovine Ovary: A Histological and Immunohistochemical Study

Abstract

Although many aspects of ovarian differentiation have been established, comparatively little is known about prenatal follicle formation and differentiation of bovine ovaries. The objective of this investigation was to study the role of the surface epithelium during the development of germ cell nests, germ cell cords and follicle formation in the fetal bovine ovary. Associated important proliferation and apoptotic features were further investigated. Additionally, the expression pattern of the S100 protein was detected. A strong increase of mitotic figures was detected in the surface epithelium, germ cell nests and germ cell cords of ovaries with a crown-rump length (CRL) of 13.0-58.0 cm. Oocytes were positively stained with S100 in bovine ovaries from fetuses with a CRL of 21.0 cm. The staining intensity enhanced parallel to increasing oocyte and follicle sizes during the ovary development. In later stages, a strong staining for S100 was observed in healthy oocytes in contradistinction to atretic oocytes where no expression of the S100 protein could be found. In conclusion, increasing mitosis index of surface epithelium cells, as well as oogonia directly beneath the surface epithelium, in combination with open surface connection during stages from a CRL of 11.0-94.0 cm of bovine fetal ovaries could play an important role in the period of time of ongoing folliculogenesis and derivation of granulosa cells. Additionally, S100-positive oocytes in primordial and later follicle stages joined by a high rate of Ki67-positive index in surrounding granulosa cells indicate that in the oocytes the S100 protein can perhaps be a useful marker for intact oocytes in bovine ovaries.

Development of mammalian ovary

“…7A). In support of this, both Garverick et al (2010) and Kenngott et al (2013) noted the lack of a well-formed epithelium in developing ovarian tissues in cattle, while McNatty et al (2000) also reported a less-prominent epithelial layer following initial formation of the gonadal ridge. Further evidence supporting the lack of a mature ovarian surface epithelium comes from the observation that surface epithelial expression of ESR1, a characteristic of the ovarian surface epithelial layer is not noted until at least day 55 in sheep and day 75 in cattle (Garverick et al 2010).…”

“…However, these migrating cells are exclusively endothelial cells, which form the testis-specific vasculature (Jeays-Ward et al 2003, Combes et al 2009). In contrast in sheep, mesenchymal cells of the giant nephron are thought to migrate into the ovary before sexual differentiation (Zamboni et al 1979), a phenomenon also observed in cattle (Kenngott et al 2013). In addition, in cattle the presence of mesonephric-tissue-derived GREL cells also appears to precede sexual differentiation.…”

Estudo de ovários fetais equinos: uma abordagem histológica1

“…A diminuição gradativa dos cordões ovígeros parece ser uma caracterís-tica conservada ao longo do processo evolutivo e tem sido relatada em outras espécies de mamíferos, como por exemplo, em macacas (Fouquet & Dang 1980), ovelhas (Sawyer et al 2002), bovinos (Kenngott et al 2013) e seres humanos (Konishi et al 1986), bem como na espécie de codorna Coturnix coturnix japonica (Madekurozwa 2012).…”

Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) pre-exposure ensures follicle integrity during in vitro culture of ovarian tissue but not during cryopreservation in the domestic cat model

“…The protocol of granulosa cell proliferation by using Ki-67 immunostaining was adapted from a previous study [23]. After histological tissue preparation, sections were treated for antigen retrieval in an autoclave machine (121°C, 1.2 kg/cm 2 ) for 30 min in citrate buffer (pH = 6.0).…”