Isolation and ultrastructural characterization of preantral follicles in the Nelore breed cows (Bos taurus indicus)

Abstract

Preantral follicles from 41 Nelore breed cows were described quantitative and ultrastructurally in the study. In the average, 35,539.20 preantral follicles were mechanically isolated (Tissue Copper) per animal. Follicles were processed for transmission electron microscopy. Primordial follicles presented an oocyte surrounded by a flattened granulosa cell layer, with some granulosa cells showing cuboidal shape. Other development stages were classified as primary follicles, with a granulosa cell layer around the oocyte and secondary stages, with oocyte surrounded by two or more cuboidal granulosa cell layer. Primordial follicles showed an evident oocyte, with the nucleus located at an eccentric cytoplasm position and a well-defined nucleolus, with condensed chromatin areas. Organelles were centered at the peri-nuclear area, showing mostly round shaped mitochondria. Follicles under development showed an increasing number of organelles and elongated mitochondria. Adherence zones, coated pits and endocitose vesicles maintained the oocyte-granulosa cell interfaces. The zona pellucida (ZP) appeared in primary follicles, showed small microvilos and many vesicles, which permeated into the ZP. Secondary follicles presented clusters of cortical granules associated to Golgi complexes. In conclusion, the mechanical method provide a sufficient amount of preantral follicles from Nelore breed cows and, due to ultrastructural similarity with follicles from other breed, it is possible to use same protocols of culture, since the oocyte meiotic maturation is kept intact.