Expression profiling of tetraploid mouse embryos in the developmental stages using a cDNA microarray analysis.

Tetraploid embryos normally develop to the blastocyst stage before implantation, but fail to survive after implantation. To better understand these characteristics of the tetraploid embryo, we produced tetraploid embryos by electrofusion and analyzed expressed genes that participated in mammalian embryogenesis using a DNA microarray analysis and a publicly available bioinformatics analysis of hatched tetraploid and diploid blastocysts. Transcriptome analysis with the DNA microarray revealed that the expression level of most genes was almost the same between diploid and tetraploid blastocysts. We found that the expression levels 2,800 genes were increased, but the expression levels over 1,600 genes were decreased in tetraploid blastocysts, which have a genomic composition identical to that of diploid blastocysts. In tetraploid blastocysts, the levels of 15 genes were decreased more than two-fold compared with the levels in diploid blastocysts. Among these downregulated genes, Ccnb1 (cyclin B1), which was decreased by 3-fold, seemed to play a particularly important role in the cellular organization of the tetraploid blastocyst. To classify the major functional classes of all the genes differentially expressed between diploid and tetraploid blastocysts, we employed a publicly available bioinformatics database, the VisuaL Annotation Display (VLAD). VLAD revealed several altered pathways in tetraploid blastocysts. Some of the enhanced biological processes were moderately involved with chromosome organization, while the suppressed processes were significantly involved with cell division and the mitotic cell cycle, metabolic processes and protein localization and transport. Taken together, our results revealed a large population of downregulated genes in tetraploid hatched blastocysts, and our convergent data suggest that the downregulation might primarily individualize the tetraploid phenotype in hatched blastocysts.