Molecular cloning of cellular apoptosis susceptibility (CAS) gene in Oreochromis niloticus and its proposed role in regulation of non-specific cytotoxic cell (NCC) functions

Cellular apoptosis susceptibility (CAS) gene is a homologue of the chromosome segregation gene (CSE) in yeast, involved in multiple cellular mechanisms associated with cell proliferation as well as cell death. CAS is highly expressed in proliferating cells but at a lower level in quiescent cells and tissues. Therefore it appears that CAS may play an important role in cancer development. We have previously identified CAS in tilapia non-specific cytotoxic cells (NCC) with a cross-reacting monoclonal antibody. Its expression was up-regulated in NCC in response to apoptosis regulatory factors. In the present report, the molecular cloning and expression of CAS in NCC is described, suggesting the importance of this protein in regulation of teleost immune functions. Furthermore, CAS expression is proposed as one of the mechanisms of regulation of activation induced programmed cell death (AIPCD) in these cytotoxic cells. As CAS expression is ubiquitous, we expect that these studies will help identify proliferating cells protected from apoptosis in additional tissues.