INTERNUCLEOSOMAL DNA FRAGMENTATION AND PROGRAMMED CELL-DEATH (APOPTOSIS) IN THE INTERDIGITAL TISSUE OF THE EMBRYONIC CHICK LEG BUD

In this work we have attempted to characterize the programmed cell dea th process in the chick embryonic interdigital tissue. Interdigital ce ll death is a prominent phenomenon during limb development and has the role of sculpturing the digits. Morphological changes in the regressi ng interdigital tissue studied by light, transmission and scanning ele ctron microscopy were correlated with the occurrence of internucleosom al DNA fragmentation, evaluated using agarose gels. Programming of the cell death process was also analyzed by testing the chondrogenic pote ntial of the interdigital mesenchyme, in high density cultures. Our re sults reveal a progressive loss of the chondrogenic potential of the i nterdigital mesenchyme, detectable 36 hours before the onset of the de generative process. Internucleosomal DNA fragmentation was only detect ed concomitant with the appearance of cells dying with the morphology of apoptosis, but unspecific DNA fragmentation was also present at the same time. This unspecific DNA fragmentation was explained by a preco cious activation of the phagocytic removal of the dying cells, confirm ed in the tissue sections. From our observations it is suggested that programming of cell death involves changes before endonuclease activat ion. Further, cell surface changes involved in the phagocytic uptake o f the dying cells appear to be as precocious as endonuclease activatio n.