Exploring the potential of prepubertal oocytes: a small ruminant model

Juvenile in vitro embryo transfer (JIVET) employs oocytes from prepubertal females to reduce generation intervals. In human, it offers potential applications for fertility preservation in young cancer patients. Ruminant animals are good models for human research because of similar follicular dynamics and oocyte competence. Several studies have shown low embryo development of prepubertal oocytes. However, oocytes from follicles larger than 3 mm can develop into blastocysts at rates comparable to oocytes from adults. This review analyzes biomarkers of oocytes as a function of follicle size (larger or smaller than 3 mm). Follicular fluid from prepubertal females contains lower levels of n-3 fatty acids than that of adults; expression of epidermal growth factor receptor (EGFR) receptor in cumulus cells is higher in large than small follicles; the condensed germinal vesicle (GV) configuration is similar in prepubertal females to the adult ones, and prepubertal large follicles and oocytes are more susceptible to oxidative stress than adult ones. In vitro maturation (IVM) strategies have been investigated: capacitation IVM (CAPA-IVM) increases EGF receptor expression and promotes GV compaction; supplementation with bone morphogenetic protein 15 (BMP15) increases EGF receptor expression; and addition of antioxidants to IVM is essential. In conclusion, oocyte competence seems to be more related to follicular state than to female age, highlighting the importance of follicular selection and optimization of IVM conditions for improving JIVET outcomes.