BACKGROUND:

Preimplantation development is a crucial step in early human development. However, the molecular basis of human preimplantation development is not well known.

METHODOLOGY:

By applying microarray on 397 human oocytes and embryos at six developmental stages, we studied the transcription dynamics during human preimplantation development.

PRINCIPAL FINDINGS:

We found that the preimplantation development consisted of two main transitions: from metaphase-II oocyte to 4-cell embryo where mainly the maternal genes were expressed, and from 8-cell embryo to blastocyst with down-regulation of the maternal genes and up-regulation of embryonic genes. Human preimplantation development proved relatively autonomous. Genes predominantly expressed in oocytes and embryos are well conserved during evolution.

SIGNIFICANCE:

Our database and findings provide fundamental resources for understanding