C-type natriuretic peptide treatment before in vitro maturation enhances maturation of yak oocytes and developmental competence of their crossbred embryos

The effects of C-type natriuretic peptide (CNP) pre-treatment on the in vitro maturation (IVM) and developmental competence of yak (Bos grunniens) oocytes were evaluated. The results showed that 100 nM CNP could effectively maintain meiotic arrest of yak oocytes in vitro within 6 h. Yak oocytes matured in two-step IVM (pre-IVM with 100 nM CNP for 6 h followed by conventional IVM for 28 h) yielded a significantly (P < .05) increased cleavage rate, blastocyst rate after in vitro fertilization with cattle spermatozoa compared to the conventional one-step IVM method. The density of transzonal projections (TZPs) decreased after 6 h standard IVM (P < .05), whereas, COCs pre-IVM with 100 nM CNP for 6 h maintained the same density of TZPs compared to the fresh COCs. This pre-IVM resulted in lesser reactive oxygen species level (P < .05). Two-step IVM resulted in the increased glutathione levels, mRNA expression levels of BCL2, BMP15, and GDF9 (P < .05) in oocytes. In conclusion, these results indicate that CNP treatment (100 nM, 6 h) before IVM could enhance the maturation of yak oocytes and developmental competence of their crossbred embryos. This may have important applications in in vitro production of yak crossbred embryos.