Insulin-like growth factor 2: a modulator of anti-apoptosis related genes (HSP70, BCL2-L1) in bovine preimplantation embryos.

Intrinsic defects within the embryos, reflected by elevated cell death and low proliferative ability, are considered the most critical factors associated with bovine infertility. The identification of embryonic factors, which are responsible for successful embryo development, is thus critical in designing strategies for infertility intervention. In this experiment, the possible mechanisms involved in both blastomere proliferation and regulation of cell death were studied by analysis of relative expression patterns of IGF-II, BCL2-L1, BAK1, and HSP70 in 3 classes of morphological quality groups (e.g., excellent, good, and poor) of bovine blastocysts produced by IVF. Variation in total blastocyst cell numbers as well as their allocation to inner cell mass and trophectoderm lineages were also determined by differential CDX2 staining. Results showed that transcript levels for IGF-II, BCL2-L1, and the BCL2-L1/BAK1 ratio were higher in excellent- and good-quality blastocysts compared with low-quality blastocysts (P < 0.01), whereas mRNA levels for HSP70 were higher in low-quality blastocyst compared with excellent-quality bovine blastocysts (P < 0.05). In addition, excellent-quality blastocysts displayed not only greater total cell number but also greater mean inner cell mass/total cell number proportion than that of poor-quality blastocysts (P < 0.01). The expression levels of IGF-II showed negative correlation with the levels of HSP70 (r = −0.70; P < 0.05); however, the correlation of expression levels of IGF-II with both of BCL2-L1 (r = 0.91; P < 0.01) and the ratio of BCL2-L1/BAK1 (r = 0.78; P < 0.05) were highly positive. There was no correlation between the expression levels of IGF-II and BAK1 genes. In conclusion, these observations suggested that levels of endogenous IGF-II transcripts might be associated with the quality of IVF embryos by regulating either apoptosis-related genes or mitogenic actions in bovine preimplantation embryos.