Buffalo (Bubalus bubalis) Pre‐antral Follicle Population and Ultrastructural Characterization of Antral Follicle Oocyte

Abstract

The main objectives of the present study were to determine the ultrastructural modifications occurring in the oocyte during late folliculogenesis and to estimate pre-antral follicle population in buffalo. Half the collected ovaries were fixed and prepared for optic microscopy; the antral follicles from the other ovaries were measured and individually punctured. The cumulus-oocyte complexes (COCs) were processed for transmission electron microscopy. The number of pre-antral follicles in buffalo ovaries was estimated at 19 819 structures. Cumulus-oocyte complexes derived from 1-mm antral follicle had an eccentrical nucleus and compact corona radiata, ooplasm vilosities were fully embedded in zona pellucida (ZP) and a well-defined junction could be observed. Mitochondria were predominantly round and well distributed in ooplasm, as were small lipid vacuoles. In COCs derived from 2-mm antral follicles, the initial formation of perivitelline space was observed. The nucleus was peripherally located and the number of pleomorphic mitochondria increased. Cortical granules were clustered at oocyte periphery and lipid vacuoles increased in number and size. In COCs derived from 6-mm antral follicles, the organelles were located mainly in the perinuclear region. Golgi complexes and smooth endoplasmic reticulum (SER) were more developed. Mitochondria migrated to the cortical region and lipid vacuoles migrated to the medullar region. In COCs derived from 10-mm antral follicles, the lipid vacuoles coalesced and occupied the medullar region of the oocyte, together with a well-developed SER. Mitochondria were pleomorphic and located at the oocyte periphery. In conclusion, the morphological differences described in this paper could be responsible for some functional differences observed in in vitro embryo production and follicular dynamics for buffalo, when compared with cattle.

Ovarian folliculogenesis in collared peccary, <i>Pecari tajacu</i> (Artiodactyla: Tayassuidae).

“…Ovarian follicular quantification varies highly among species. In buffaloes (Bubalus bubalis), the average number of primordial, primary, and secondary follicles is 3 518.98±1 988.37, 14 672.03±12 263.76 and 1 628.29±1 182.24, respectively (Mondadori et al 2010), while in mice (100 days of age) it is 2 227±101, 265±32 and 79±5.6, respectively (Myers et al 2004). Gosden & Telfer (1987) observed that in some species the number of primordial follicles varied allometrically with both body weight and maximum life expectation, and the difference in the follicular number between species could be a strategy, which guarantees fecundity throughout most of the lifespan.…”

Ultrastructural changes in oocytes during folliculogenesis in domestic mammals

“…The supply of preantral follicles per ovary is highly variable among species [20] and has been estimated at 70,576 in Bos indicus [32] and 89,577 in Bos Taurus [33], 19,819 in buffaloes [34], 75,642 in sheep [35], 37,646 in goats [36], 402,000 in humans [37], 106,071 in monkeys ( Cebus apella ) [38], 37,853 in domestic cats [39], 210,00 in pigs [40] and 47,900 in domestic dogs [41]. …”

“…Some early biochemical studies showed that the synthesis of lipids (such as the triacylglycerol stored on lipid droplets) requires enzymatic activity associated with both the endoplasmic reticulum and mitochondria, with lipids being transported and transferred between the endoplasmic reticulum and mitochondria (For a review see [61]). As the follicle grows, the number of these metabolic units in the ooplasm increases, denoting a rise in oocyte metabolism [34]. In goats, buffaloes and sheep, many vesicles are spread throughout the cytoplasm and they present different electron densities [45],[47],[62], which might mean different contents, like proteins or mucopolysaccharide [63].…”

“…Oocytes of secondary follicles are predominantly spherical and present a cytoplasm with vesicles and round and elongated mitochondria in cows [44],[57],[78], sheep [79], goats [36],[47],[80], cats [39], buffaloes [34],[45], humans [54],[81] and yaks [52]. …”

Estimation, morphometry and ultrastructure of ovarian preantral follicle population in agouti (Dasyprocta leporina)

“…According to Mondadori et al (2010), the location of this organelle into the oocyte varies according to the follicle development and it appears to be more developed in growing follicles than in the early PFs, consistent with the higher metabolism and requirement for protein and lipids of those oocytes (Paulini et al 2014).…”