PROGRAMMED CELL-DEATH IN AVIAN THYMOCYTES - ROLE OF THE APOPTOTIC ENDONUCLEASE

Apoptosis, or programmed cell death, is a physiological process whereb y a target cell dies in response to a specific signal. A prominent mod el system used to study this process is the glucocorticoid-mediated ki lling of immature thymocytes. Following glucocorticoid treatment, apop totic thymocytes undergo a series of distinct morphological alteration including cellular shrinkage, blebbing of the cytoplasmic membrane, a nd chromatin condensation. The chromatin condensation that occurs duri ng apoptosis is associated with a characteristic endonuclease activity that degrades the genome at internucleosomal sites. To study this cha racteristic endonuclease activity further, nuclear extracts were prepa red from thymocytes of glucocorticoid-treated chicks and nuclease acti vity present in the protein extracts was analyzed using chicken red bl ood cell nuclei as a substrate. Using this in vitro assay system, it w as demonstrated that the avian endonuclease activity degrades chromati n at internucleosomal sites and can be inhibited by EDTA and zinc ions . Current efforts are focused on purifying the avian apoptotic endonuc lease and further characterizing this nuclease activity.