Cell death: Defining and misshaping mammalian embryos

Abstract

Cell death has long been known to be a normal part of embryonic development, typically sculpting the body, removing vestigial or sexually incongruent tissues, generating lacunae and separation of tissue layers, and playing other important roles in morphogenesis. The germ line manifests considerable death of supporting cells, presumptively defective cells, and oocytes that may initiate but not complete maturation, and the differentiation of spermatocytes involves apoptosis-like activity. Most of the deaths are apoptotic. Although in nonmammalian embryos one does not encounter nonpathological deaths before the maternal-zygotic transition, in mammalian embryos spontaneous cell death begins at the end of compaction. Many embryonic defects are associated with abnormal patterns of cell death. However, it is usually not clear whether the abnormality is a cause or result of the defect.