BioProject

Preimplantation development is a crucial step for successful implantation and pregnancy. More...

Preimplantation development is a crucial step for successful implantation and pregnancy. Although both compaction and blastocyst formation have been extensively studied, mechanisms regulating early cell division stages before compaction have remained unclear. Here, we show that ERK MAP kinase function is required for early embryonic cell division and normal cell-cell adhesion before compaction. Our analysis demonstrates that inhibition of ERK activation in the late 2-cell stage embryos leads to a reversible arrest in G2 phase in the 4-cell stage. The G2 arrested, 4-cell stage embryos show weakened cell-cell adhesion as compared to control embryos. Remarkably, microarray analyses show that most of the programmed changes of upregulated and downregulated gene expression during the 4- to 8-cell stages normally proceed in the 4-cell stage-arrested embryos, except for a portion of the genes whose expression profiles closely parallel the stages of embryonic development when arrested in G2 and released to resume development. These parallel genes include the genes encoding intercellular adhesion molecules, whose expression is found to be positively regulated by the ERK pathway. We also show that while ERK inactivation in the 8-cell stage embryos does not lead to cell division arrest, it does cause cell division arrest when cadherin-mediated cell-cell adhesion is disrupted. These results demonstrate an essential role of ERK function in the G2/M transition and the expression of adhesion molecules during the 2-cell to 8-cell stage embryos, and suggest a loose parallelism between the gene expression programs and the developmental stages before compaction. Keywords: preimplantation development Overall design: We examined expression profiles of genes during early cell division stages in mouse preimplantation development. We performed the genome-wide analysis by using Affymetrix GeneChip oligonucleotide microarrays, and examined the effect of the ERK pathway inhibitor U0126 on the expression profiles. Two independent experiments were carried out. We collected embryos at six points as follows; control embryos at day 1.5 (cont. 1.5, 2-cell stage), day 2.5 (cont. 2.5, 4- to 8-cell), and day 3.5 (cont. 3.5, morula to blastocyst), and the U0126-treated embryos at day 2.5 (U2.5, 4-cell arrested), embryos released from the U0126-induced arrest at day 3.5 (U3.5, 8-cell) and at day 4.5 (U4.5, morula to blastocyst). Hybridization was carried out with the Mouse Genome 430 2.0 array following Affymetrix instructions. Hybridized arrays were scanned using an Affymetrix GeneChip Scanner. Expression analysis was performed using GeneChip Operating Software v. 1.2 (GCOS) and GeneSpring 7.3. Less...