OCCURRENCE OF DNASE GAMMA-LIKE APOPTOTIC ENDONUCLEASES IN HEMATOPOIETIC-CELLS IN XENOPUS-LAEVIS AND THEIR RELATION TO METAMORPHOSIS

DNase gamma has been suggested to be an endonuclease responsible for t hymic apoptosis in mammals. Using the frog, Xenopus laevis, we examine d whether any hematopoietic cells other than thymocytes have DNase gam ma activity. The activity gel assays and HeLa cell nuclear assays for DNase revealed that nuclei from red blood cells and cells in liver (an erythropoietic organ) contain DNase gamma-like activities (molecular mass of 38 and 36 kDa) indicated by their biochemical features (intern ucleosomal DNA cleavage, requirement of Ca2+ and Mg2+, and sensitivity to Zn2+). Distribution of these two (38 and 36 kDa) forms of enzyme w as determined by cell fractionation analysis of liver cells: the 38 kD a form of enzyme was found in erythrocytes/erythroblasts and hepatocyt es, whereas the 36 kDa form was in lymphocytes/macrophages. Interestin gly, these two enzyme activities increased during metamorphic climax, at which time larval-type cells are converted to adult ones. It thus a ppears that these gamma-type DNases are involved in programmed cell de ath during metamorphosis. (C) 1997 Academic Press.