Transcript profiling of individual twin blastomeres derived by splitting 2-cell stage murine embryos

We have examined whether twin blastomeres from 2-cell stage mouse embryos differ in mRNA content. Amplified mRNA from 12 blastomeres derived from six embryos approximately mid-way through their second cell cycle was analyzed. Probes displaying normalized values greater than 0.25 were selected and examined for consistent bias in expression within blastomere pairs. Although transcript content varied both between individual embryos and twin blastomeres, no consistent asymmetries were observed for the majority of genes. On the other hand, 769 genes displayed a greater than 1.4-fold difference in expression across 5 of 6 pairs of blastomeres and 178 genes differed across all 6 pairs. These genes separated into two groups by class discovery clustering. Of the 769 differentially expressed genes, 163 were significantly up- or down-regulated in one sister blastomere compared to the other. Transcripts encoding proteins implicated in RNA processing and cytoskeletal organization were highly represented among the most abundant, differentially distributed mRNA. We conclude that there are many differences that distinguish twin blastomeres derived from a single 2-cell stage embryo but that only a few of these differences are consistent across multiple pairs of embryos. We hypothesize that a stochastically-based lack of synchrony in cell cycle progression between the two cells might explain some or all of the asymmetries in transcript composition. 6 pairs of blastomeres were analyzed for a total of 12 samples.