Detection of apoptosis by electron microscopy and in situ labelling in the rat olfactory pit.

The purpose of this study was to provide further information upon the cell death process by apoptosis occurring in the olfactory pit during the primary palate formation and the vomeronasal organ detachment. Apoptotic cells were detected by coupling ultrastructural observations and in situ end-labelling of DNA breaks (TUNEL labelling) in E12-E15 rat embryos. During the primary palate formation and the vomeronasal organ closure, a strong apoptotic cell death process was observed along the midline epithelial seam after the epithelial fusion. The topographical distribution of labelled nuclei was in agreement with the morphological distribution of dying cells. One day before the nasal swellings fused, numerous degenerating cells were also detected in the regions of prospective contact which thus appeared as regions of programmed cell death.