Bcl-xL is a negative regulator of caspase-3 activation in immature neuronsduring development

Caspases and Bcl-xL, the mammalian homologues of the Caenorhabditis elegans (C. elegans) ced-3 and ced-9 genes, respectively, regulate apoptosis of va rious cells. Caspase-3 is processed into an active form (p20 or p17 and p12 ) during apoptosis. We investigated the relation between caspase-3 and Bcl- xL during development by examining activation of caspase-3 and apoptotic ce lls in Bcl-x-deficient (bcl-x(-/-)) mice at embryonic (E) day 11.5, We used a double-staining technique with a cleavage site-directed antibody against caspase-3 (anti-p20/17) and terminal-deoxytransferase-mediated deoxyuridin e triphosphate nick-end labeling (TUNEL). Bcl-xL-deficiency increased both numbers of p20/17-positive and -negative apoptotic cells in dorsal root gan glia (DRG); the numbers of p20/17-positive apoptotic cells in the caudal pa rts of the ventral hindbrain and ventral spinal cord; and the numbers of p2 0/17-negative apoptotic cells in the dorsal midbrain, dorsal hindbrain, and dorsal spinal cord. Thus, Bcl-xL blocks the caspase-3-dependent apoptotic pathway in the restricted regions of the nervous system during development. Furthermore, these observations suggest that Bcl-xL protects against activ ation of the caspase-3-independent apoptotic pathway. Other caspases or apo ptotic mechanisms may also be activated in the nervous systems of bcl-x(-/- ) mice. (C) 1999 Elsevier Science B.V. All rights reserved.