Morphological characteristics of dying cells in axial structures of developing human embryos

Programmed cell death (PCD) is a widespread phenomenon in the development o f vertebrates. In most cases, dying cells during development exhibit genera lized morphological features typical of apoptosis. We analyzed the morpholo gical features of dying cells in the developing axial structures of 5 human embryos between 5 and 8 weeks of postovulatory age. Cell death in the axia l structures, i.e. spinal cord, notochord and surrounding mesenchyme and so mites, was analyzed using light and electron microscopy. Tissue samples wer e taken from the cervicothoracic region of normal human conceptuses. Two mo rphological types of cell death were found: apoptosis which was characteriz ed by round or semilunar nuclear chromatin condensations, condensation and shrinkage of the cytoplasm and formation of apoptotic bodies, and cell deat h without the morphological features of apoptosis which was characterized b y pyknotic nuclear chromatin condensations, vacuolated cytoplasm and the fo rmation of numerous intercellular spaces. Apoptotic death occurred during t he 5th week of normal development in all the axial structures. Later, apopt otic death appeared in all the axial structures, with the exception of the notochord, where some dying cells displayed features of secondary necrosis. According to our findings, apoptosis seems to be the most frequently obser ved type of PCD, but it is not the exclusive type of morphological cell dea th during the development of axial structures in human embryos. Copyright ( C) 2001 S. Karger AG, Basel.