Embryo

Regulation of Gene Expression in Bovine Blastocysts in Response to Oxygen and the Iron Chelator Desferrioxamine

Abstract
Low (2%) oxygen conditions during post-compaction culture of bovine blastocysts improve embryo quality and are associated with small increases in the expression of glucose transporter 1 (SLC2A1), anaphase promoting complex (ANAPC1) and myotrophin (MTPN), suggesting a role for oxygen in regulation of embryo development, mediated through oxygen-sensitive gene expression. However, bovine embryos, to at least the blastocyst stage, lack detectable levels of the key regulator of oxygen-sensitive gene expression, hypoxia-inducible 1 alpha (HIF1alpha), while the less-well characterized HIF2alpha protein is readily detectable. Here we report that other key HIF1 regulated genes are not significantly altered in their expression pattern in bovine blastocysts in response to reduced oxygen concentrations post-compaction, with the exception of lactate dehydrogenase A (LDHA), which was significantly increased following 2% oxygen culture. Antioxidant enzymes have been suggested as potential HIF2 target genes, but their expression was not altered following low oxygen culture in the bovine blastocyst. The addition of desferrioxamine, an iron chelator and inducer of HIF regulated gene expression, during post-compaction stages significantly increased SLC2A1, LDHA, inducible nitric oxide synthase (NOS2A) and MTPN gene expression in bovine blastocysts, although development to the blastocyst stage was not significantly affected. These results further suggest that expression of genes, known to be regulated by oxygen via HIF-1 in somatic cells, is not influenced by oxygen during preimplantation postcompaction bovine embryo development. Oxygen regulated expression of LDHA and SLC2A1 in bovine blastocysts suggests that regulation of these genes may be mediated by HIF2 in the bovine embryo. Furthermore, the effect of a reduced oxygen environment on gene expression can be mimicked in vitro through the use of desferrioxamine. These results further support our data that the bovine blastocyst stage embryo is unique in its responsiveness to oxygen compared with somatic cells, in that the lack of HIF1-mediated gene expression reduces the overall response to low (physiological) oxygen environments, which appear to, if anything, favor development.

Key words: Embryo • Environment • Developmental biology • Early development • Gene regulation

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