Characterization of folliculogenesis and the occurrence of apoptosis in the development of the bovine fetal ovary

Abstract

The aim of this research was to perform in situ quantification, morphometry evaluation, and apoptosis analysis of ovarian follicular wall cells in mechanically isolated follicles obtained from ovaries of bovine fetuses (Bos taurus indicus) between 3 and 9 months of age. Apoptosis was evaluated using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. The number of isolated follicles increased from 3 months onward (102.5 ± 141.1, mean ± SEM), peaked at 6 months (12855.0 ± 9030.1), and then decreased by 7 months (3208.7 ± 3249.5), consistent with atresia occurring at these stages. Follicular density was greatest at 4 months, consistent with a sudden boost in follicular activity independent of a corresponding increase in ovarian size. Antral follicles were first observed at 5 months. As fetal age increased, there was a tendency for the percentage of primordial and primary follicles to decrease, and the percentage of secondary follicles to increase. However, the high variability (P < 0.05) for all follicle populations up to 5 months of age precluded further interpretation of these results. Oocyte diameter increased from the primordial (23.6 ± 4.4 μm) to the secondary follicular stages (38.0 ± 14.9 μm). Apoptosis was observed in ovaries from all fetal ages analyzed. We concluded that preantral follicles could be isolated from bovine fetuses by 3 months of age, with apoptosis affecting ovarian follicular dynamics throughout fetal life.

Morphometric and gene expression analyses of stromal expansion during development of the bovine fetal ovary

“…An earlier morphometric study examining the bovine fetal ovary has been conducted but over a shorter period of time than our study. From their results we calculated that the ovary volume increased 4.2 fold in volume (35 to 148 mm 3 ), the cortex increased 2.8 fold in volume (21.9 to 62.4 mm 3 ) and the medulla increased 6.5 fold (13.1 to 85.6 mm 3 ) from 3 to 7 months of gestation (Santos et al 2013). Our measurements are in agreement with theirs where, during Stages I to III (taking 94 days) versus Stages III to V (taking 91 days) the changes in ovarian weight were 6.2 and 4.2 fold, in medullary volume were 6.3 and 7.6 fold and in cortical volume were 6.7 and 2.0 fold respectively.…”

Comparison between Slow Freezing and Vitrification in Terms of Ovarian Tissue Viability in a Bovine Model

“…Data are in agreement with previous findings, which showed that the proportion of primordial follicles was higher than that of other stages in bovine ovaries. 27 Kim et al 28 suggested that the pool of primordial and primary follicles would be responsible for the resumption of hormone production and the generation of pregnancy after transplanting ovarian tissue back to the patient. However, the quantity and diversity of follicles necessary for a successful retransplantation is still a factor to be determined.…”

Multifaceted programmed cell death in the mammalian fetal ovary

“…Moreover, the TUNEL staining, generally used for detecting DNA fragmentation resulting from apoptotic cascade, at least in vivo and at early stages of meiotic prophase I, does not seem to be a reliable marker for apoptosis in all fetal oocytes (for references, see De Felici and Klinger, 2011). Recent papers on the buffalo and cattle and mouse fetal oocytes as well, also led to such conclusion, focusing on PARP-1 as a more suitable marker of oocyte apoptosis (Santos et al, 2013;Ene et al, 2013).…”