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Initial differentiation of blastomeres in 4-cell human embryos and its significance for early embryogenesis and implantation


This brief review is devoted to the nature of early blastomere differentiation in human 4‐cell embryos and its consequences for embryonic development. Precursor cells of inner cell mass, germline, and trophectoderm may be formed at this stage, the clearest evidence being available for trophectoderm. The sites of these precursor cells in the embryo could be ascertained using markers for animal and vegetal poles, observing specific cleavage planes, and assessing gene and protein expression. This opens new opportunities for studying 4‐cell embryos and removing or replacing specific cells. Knowledge of the properties of individual blastomeres should help in improving assisted human reproduction, performing preimplantation genetic diagnosis, and perhaps establishing specific stem cell lines. Special attention is paid to well-characterized trophectoderm, the trophectoderm stem cell, and possible new forms of clinical application.

Keywords: blastomere allocation, germline, inner cell mass, preimplantation human embryogenesis, stem cells, trophectoderm.


a Chief Editor, Reproductive BioMedicine Online, Duck End Farm, Dry Drayton, Cambridge CB3 8DB, UK

b Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, University of Southern California Keck School of Medicine, 1240 North Mission Road, Los Angeles, CA 90033, USA

* Corresponding author.

# Original publication: Edwards, R.G. and Hansis, C., 2005. Initial differentiation of blastomeres in 4‐cell human embryos and its significance for early embryogenesis and implantation. Reprod. BioMed. Online 11, 206–218.