Comparative gene expression analysis of bovine nuclear-transferred embryos with different developmental potential by cDNA microarray and real-time PCR to determine genes that might reflect calf normality.

Placental abnormalities are the main factor in the high incidence of somatic cell clone abnormalities. The expression of several trophoblast cell-specific molecules is enhanced during gestational days 7 to 14. To determine the possible genes whose expression patterns might reflect calf normality, we first compared the gene expression profiles on day 15 between in vitro-fertilized (IVF) embryos and two types of somatic cell nuclear-transferred embryos with either a high (FNT) or low (CNT) incidence of neonatal abnormalities using a cDNA microarray containing 16 of 21 placenta-specific genes developed from tissues collected across gestation. To identify significant genes from the screening of day 15 embryos, genes with a less than two-fold difference in expression between IVF and CNT embryos, and those with a greater than two-fold difference between IVF and FNT and between CNT and FNT were considered to contribute to clone abnormalities. These two comparisons revealed 18 down-regulated and 18 upregulated genes of the 1722 genes examined. We then examined the expression levels of 10 genes with known functions in eight-cell and blastocyst-stage embryos by real-time PCR. The mRNA expression pattern of interferon (IFN)-tau, a trophectoderm-related gene, differed between IVF, CNT, and FNT eight-cell embryos; few or none of the IVF or CNT eight-cell embryos expressed IFN-tau mRNA, but all eight-cell FNT embryos expressed IFN-tau. IFN-tau mRNA expression was significantly higher in IVF blastocysts, however, than in nuclear-transferred blastocysts. Average IFN-tau mRNA expression in FNT blastocysts was not different from that in CNT blastocysts, due to one CNT blastocyst with high expression. The precise relation between early expression of IFN-tau mRNA and inferior developmental potential in cloned embryos should be examined further.