The tissue dynamics of heart morphogenesis. I. The phenomena of cell death. A. Identification and morphology.

Abstract

1. The morphology and some histochemical aspects of spontaneous cell death associated with the development of the chick embryo heart were studied. 2. The degenerative phenomena in the bulbar cushions on the 4th to 5th day of incubation, as based on hematoxylin-eosin staining, were ascertained by means of methyl green-pyronine staining, PAS, Feulgen and acid phosphatase reactions, supravital Nile blue sulphate and neutral red stainings as well as electron microscopy. 3. The degenerating, dying or dead cells were found to be Feulgen-positive. Some were PAS-positive. The staining pattern with methyl green-pyronine indicated DNA and RNA materials. 4. The macrophages appearing on the 5th day of incubation in bulbar cushions stained supravitally with Nile blue sulphate and neutral red, and large quantities of acid phosphatase could be demonstrated. 5. The electron microscope studies confirmed increased autophagic activity at the begining of degeneration and the appearance of macrophages in the later stages. 6. With increasing embryonal age large pycnotic figures became rare and fine degeneration granules prevailed. 7. Until the 6th day of incubation the degenerating and/or dead cells were lysed in situ if isolated, or phagocytized by neighbouring mesenchymal cells if present in greater quantities. They could also be expelled to different tissue boundaries. 8. As from the 8th day of incubation, some of the degenerating and dead cells were concentrated around blood vessels. They were also seen in heart cavities and in blood vessel lumina.