Totipotent 8Cell human embryos may be naturally susceptible to aneuploidy

Abstract

OBJECTIVE: To compare gene expression in totipotent 8Cell human embryos with pluripotent human embryonic stem (hES) cells. DESIGN: Expression patterns of 74 genes involved in pluripotency in hES cells were compared by whole human genome microarray analyses of mRNAs in two pools of 8-Cell human embryos, two lines of pluripotent hES cells, and fibroblasts before and after induced pluripotency (iPS cells). MATERIALS AND METHODS: The 8Cell microarray studies were reviewed and approved by institutional review boards in Boston, MA and Athens, Greece. Two pools of 5 normal appearing 8Cell embryos were subjected to RNA extraction and hybridization to Agilent whole human genome microarrays and compared with two lines of hES cells for 74 pluripotency genes. Statistical analyses indicated 7-fold higher or lower levels of fluorescence were potentially biologically relevant. RESULTS: Thirty pluripotency genes were over- or under-expressed by the 8Cell embryos, including the six transcription factors: KLF4, LIN28, MYC, NANOG, POU5F1, and SOX2, shown to transform normal human fibroblasts to iPS cells. Of the six, only MYC and KLF4 were over-detected on the 8-Cell arrays, along with DPPA5, ELOF1, IMP4, TCL1A, ZNF738. LEFTY1 and -2 were surprisingly quiet in the 8-cell embryos, as was DNMT3B, GAL, PODXL, TDGF1 and TERF1. CONCLUSION: Taken together, the findings indicate the totipotent embryo cells may be naturally susceptible to aneuploidy. Since most cells in pre-blastocyst embryos will give rise to placenta, only the few cells giving rise to the pluripotent inner cell mass (ICM) must be faithfully euploid. The microarrays emphasize striking differences in gene expression profiles between totipotent 8-Cell human embryos and lines of human embryonic stem cells cultured from ICMs, suggesting checkpoints to ensure accurate chromosomal allocation to daughter cells may be established in the ICM.