Developmental competence of mature yak vitrified–warmed oocytes is enhanced by IGF-I via modulation of CIRP during in vitro maturation
The objective of this study was to investigate whether developmental competence of mature vitrified-warmed yak (Bos grunniens) oocytes can be enhanced by supplemented insulin-like growth factor I (IGF-1) during in vitro maturation (IVM), and its relationship with the expression of cold-inducible RNA-binding protein (CIRP). In experiment 1, immature yak oocytes were divided into four groups, and IVM supplemented with 0, 50, 100 and 200 ng/mL IGF-1 was evaluated; the mRNA and protein expression levels of CIRP in mature oocytes in the four groups were evaluated using quantitative real-time PCR and western blotting analyses. In experiment 2, the mature yak oocytes in the four groups were cryopreserved using the Cryotop (CT) method, followed by chemical activation and in vitro culture for two days and eight days to determine cleavage, blastocyst rates, and total cell number in the blastocysts. Mature yak oocytes without vitrification served as a control group. The outcomes were as following: (1) the expression of CIRP in the matured oocytes was up-regulated in the IGF-1 groups and was highest expression was observed in the 100 ng/mL IGF-1 treatment group. (2) In the vitrified-warmed groups, the rates of cleavage and blastocyst were also highest in the 100 ng/mL IGF-1 treatment group (81.04 ± 1.06%% and 32.16 ± 1.01%), which were close to the rates observed in groups without vitrification (83.25 ± 0.85% and 32.54 ± 0.34%). The rates of cleavage and blastocyst in the other vitrified-warmed groups were 70.92 ± 1.32% and 27.33 ± 1.31% (0 ng/mL); 72.73 ± 0.74% and 29.41 ± 0.84% (50 ng/mL); 72.43 ± 0.61% and 27.61 ± 0.59% (200 ng/mL), respectively. There was no significant difference in the total cell number per blastocysts between the vitrified-warmed groups and group without vitrification. Thus, we conclude that the enhancement in developmental competence of mature yak vitrified-warmed oocytes after the addition of IGF-1 during IVM might result from the regulation of CIRP expression in mature yak oocytes prior to vitrification.