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 follicular dynamics and oocyte competence are similar to humans. 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; cumulus cells EGF receptor expression is higher in large than small follicles; the condensed germinal vesicle (GV) configuration is similar in adult and prepubertal large follicles and prepubertal oocytes are more susceptible to oxidative stress than adults. IVM strategies have been investigated: CAPA-IVM increase EGF receptor expression and promote 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 with female age, highlighting the importance of follicular selection and optimization of IVM conditions for improving JIVET outcomes.