Agouti-signaling protein (ASIP) improves bovine in vitro matured oocyte developmental competence and modulates lipid content.

Purpose: Bovine embryos produced in vitro are developmentally inferior compared to in vivo derived embryos due to the lack of optimization of the oocyte and embryo culture conditions in vitro. Agouti-signaling protein (ASIP), a secreted protein produced by the bovine oocyte, has been recently shown to aid in acquiring oocyte developmental competence. Therefore, in the present study, we aimed to reveal the effects of supplementation of ASIP during in vitro oocyte maturation and embryo culture on subsequent embryonic development.

Methods: Cumulus-oocyte complexes or presumptive zygotes were placed in culture medium containing either 0, 1, 10, or 100 ng/mL of recombinant ASIP (rASIP). Effects on development, gene expression, lipid content, and blastocyst cell allocation were examined.

Results: Supplementation of rASIP during oocyte maturation was found to significantly increase the blastocyst development rate (P < 0.05) and produced blastocysts with an increased inner cell mass to trophectoderm cell ratio. Addition of rASIP during oocyte maturation increased oocyte (P < 0.05) but not embryo (P > 0.05) lipid levels. The expression of genes involved in lipid metabolism, including FASN, PPAR $\gamma$ , SCD, CSL1, ELOVL5, and ELOVL6, was not significantly altered in blastocysts due to treatment (P > 0.05). Supplementation of rASIP during embryo culture was not found to affect blastocyst rates.

Conclusions: The data presented in this study further support the role of ASIP in oocyte competence and suggest that the supplementation of rASIP during oocyte maturation may lead to the production of blastocyst of increased quality.