Transcript abundance and apoptosis in day-7 porcine blastocyst cultured with exogenous insulin-like growth factor-I

Exogenous growth factors may increase the efficiency of embryo development in vitro. The aim of the present study was to examine the effects of insulin-like growth factor (IGF)-I on porcine embryo development. Porcine embryos obtained by in vitro fertilization were cultured for seven days in the presence of IGF-I (50, 100 or 150ng/ml). Subsequently, relative transcript abundance (RA) of IGF-related genes (IGFR1, IGFBP2, and IGFBP3), glucose transporter genes (SLC2A4 and SLC2A8), and apoptosis-related genes (BAX and BCL-XL) was analyzed. No differences were observed in the cleavage rate on day 2 post insemination (pi) and blastocysts rate on day 7pi between IGF-treated and control embryos. IGF-I treatment did not affect RA of IGFR1, IGFBP3, and SLC2A4 genes, but decreased RA of IGFBP2 and SLC2A8 genes. The percentage of TUNEL-positive nuclei in blastocysts did not differ between the experimental groups. However, RA of BAX and BCL-XL genes decreased in response to all IGF-I concentrations, whereas the BCL-XL/BAX RA ratio was enhanced when embryos were cultured in medium containing 150ng/ml of IGF-I. These results indicate that IGF-I did not stimulate in vitro development of porcine embryos through the IGF signaling system, nor did IGF-I stimulate RA of glucose transporter genes. However, IGF-I at the highest dose was able to increase the BCL-XL/BAX transcript expression ratio. This may indicate that the primary role of IGF-I during the first days of embryo development in the pig is associated with anti-apoptotic actions rather than with growth stimulation.