Growth hormone gene expression in oocytes and zygotes produced by cows heterozygous (Leu127Val) at GH locus

The present work describes analysis of the growth hormone gene (GH) expression in non-matured and in vitro matured bovine oocytes as well as zygotes after in vitro fertilization. The Leu/Val polymorphism described in the 5th exon of the bovine GH gene was applied to investigate the expression of genetic variants in the analyzed material. Experiments were performed on oocytes collected from heterozygous (LV) cows. Since developmental stages analyzed in this study are not transcriptionally active with regard to the GH gene, the analyzed transcripts were exclusively of maternal origin. According to our findings, GH transcript was observed in each analyzed sample. The expected heterozygous pattern of GH gene expression was found in non-matured oocytes. However, an unexpected variation in allelic distribution was noticed in matured oocytes and zygotes. A tendency was observed of a gradual disappearance of the heterozygous pattern (variant LV) ranging from 100% in non-matured oocytes, 70% in matured cells and 20% in zygotes. In some of analyzed samples, the expected heterozygous pattern was replaced by the VV variant in matured oocytes and either by VV or LL variants in zygotes. Possible mechanisms underlying the described phenomenon (in vitro culture conditions, transcript polyadenylation) are discussed. These results indicate a possible influence of sub-optimal in vitro culture conditions on the distribution of genetic variants of GH gene transcripts in bovine oocytes and zygotes.