Effect of follicle size and of the FecB Booroola gene on oocyte function in sheep

Abstract

Booroola ewes have a major gene that affects ovulation rate. Gene expression has consequences on ovarian somatic cells but it is unknown whether it also affects germ cells in the adult ovary. Hence, the present study examined (1) whether oocyte growth was similar in FecBFecB and Fec+ Fec+ oocytes during preantral and antral follicular growth, (2) whether the patterns of proteins neosynthesized by oocytes of these two genotypes were identical, (3) whether the ability of the oocytes to resume meiosis was unaffected by genotype and (4) whether, after IVF, oocytes from both genotypes could develop to the blastocyst stage at similar rates. Histological examination of the respective sizes of the oocyte and of the follicle demonstrated that oocytes were larger in FecBFecB versus Fec+ Fec+ preantral follicles. Resolution of the proteins neosynthesized by FecBFecB and Fec+ Fec+ oocytes by one-dimensional PAGE and image analysis demonstrated that quantitative (but not qualitative) differences could be observed between genotypes for bands at 74, 59, 35 and 25 kDa. In addition, a genotype by oocyte size interaction was detected for two additional bands at 45 and 43 kDa. After 24 h of culture in vitro in TCM-199 plus 100 ng ml-1 FSH plus 10% sheep follicular fluid, oocytes from FecBFec+ follicles gained the ability to resume meiosis at a smaller size and a higher proportion of them reached metaphase II irrespective of the size class studied compared with Fec+ Fec+ follicles. In addition, the developmental rate of eggs after IVF was also affected by follicle size and genotype, since FecBFec+ oocytes originating from 1.0-3.5 mm follicles had a greater ability (P < 0.05) to develop to the blastocyst stage than Fec+ Fec+ oocytes. It is concluded that the FecB gene, in addition to its effects on granulosa cell maturation, also affects oocyte development and function. Whether these alterations are related requires further investigation.

Sheep embryos derived from FSH/eCG treatment have a lower in vitro viability after vitrification than those derived from FSH treatment

“…It is known that sheep as goat and bovine oocytes derived from < 1 mm follicles are incapable of resuming or completing meiosis during in vitro culture [7,9,16]. In vitro evidence suggests that, although appreciable amounts of estradiol are detected in follicles of > 0.5 mm diameter, small antral follicles respond individually and not identically to gonadotrophins indicating a hierarchical development [31].…”

“…In vitro evidence suggests that, although appreciable amounts of estradiol are detected in follicles of > 0.5 mm diameter, small antral follicles respond individually and not identically to gonadotrophins indicating a hierarchical development [31]. In sheep, the ability to progress to meiotic cycle and gain the ability to develop up to the blastocyst stage is achieved progressively as follicle diameter increases [7,18]. These negative effects due to eCG can occur before ovulation, as a consequence of an unbalanced hormonal profile during oocyte maturation or later, during early embryonic development as an inadequate capacity to cleave.…”

Pattern of follicular development in sheep subjected to ovarian superstimulation after follicular ablation by laparoscopic ovum pick-up

“…Therefore, determining the time at which the population of medium-sized follicles is largest is very important for obtaining the optimal number of high-quality COCs for in vitro embryo production (COGNIÉ et al, 1998;RODRIGUEZ et al, 2006;KARAMI-SHABANKAREH & MIRSHAMSI, 2012). The population maximum was determined using a theoretical model, and was represented by the peak of the parabolic distribution, with the highest proportion of follicles with diameters between 2.5 and 4.5mm appearing at 34.6 hours.…”

“…Multiple factors such as age (ARMSTRONG, 2001), aspiration technique, follicle diameter (COGNIÉ et al, 1996(COGNIÉ et al, , 1998KHATIR et al, 2007), oocyte diameter (DURINZI et al, 1995), presence of corpus luteum (WANIA et al, 1999), and superstimulatory treatment (BALDASSARRE et al, 1996(BALDASSARRE et al, , 2002, can influence the recovery rate and quality of cumulus oophurus complexes (COCs) obtained from animals. These factors can also influence the rate of oocyte maturation and the rate of in vitro.…”

“…During in vitro embryo production, better recovery rates and oocyte utilization are observed when the follicles collected from ewes are larger than 3mm in diameter (COGNIÉ et al, 1998). However, although large follicles are more easily visualized, the high viscosity of their Denadai et al contents may contribute to decreased recovery rates (BALDASSARE et al, 1994a;SENEDA et al, 2001).…”