Apoptosis in the human embryo

Preimplantation human embryos are characterized by various degrees of cytop lasmic fragmentation, and a high incidence of developmental arrest before t he blastocyst stage. This review examines the current morphological and bio chemical evidence that apoptosis plays a role in early human development an d embryonic loss. Embryos examined 24 h or more after arrest often show cha racteristic features of apoptosis including cytoplasmic, nuclear and DNA fr agmentation. In contrast, embryos of good morphology that appear to be deve loping normally show no evidence of apoptosis before compaction. However, a t the morula and blastocyst stages, scattered cells with fragmented nuclei and DNA characteristic of cells undergoing apoptosis are common features. A poptosis may result from suboptimal culture conditions, or may be involved in the elimination of abnormal cells. However, the causes, role and regulat ion of apoptosis in the human preimplantation embryo remain to be determine d.