IgH-2 cells: a reptilian model for apoptotic studies.

Regulation of proper cell number in tissues depends upon a balance between cell proliferation and cell death. The process of apoptosis has thus far been studied in a variety of multicellular organisms from humans to higher plants. In order to broaden our perspective and identify another metazoan system with which to deepen our understanding of the function and evolution of the apoptotic machinery, we have characterized cell death in a reptilian cell line. We show that the death of IgH-2 Iguana (Iguana iguana) heart cells [Clark, H.F., Cohen, M.M., Karzon, D.T., 1970. Characterization of reptilian cell lines established at incubation temperatures of 23 to 36 degrees. Proc. Soc. Exp. Biol. Med. 133, 1039-1047.] is, in response to DNA damaging agents, accompanied by classic morphological changes of apoptosis including detachment from the substrate, cell shrinkage, nuclear pyknosis and externalization of the plasma membrane phospholipid phosphatidylserine. Our biochemical studies show that the death of IgH-2 cells is accompanied by internucleosomal DNA fragmentation and activation of caspases. Our studies with the pan-caspase inhibitor zVAD.fmk implicate caspases in the apoptotic process we observe. This work represents the first detailed molecular and biochemical analysis of apoptosis in cells of an organism of class Reptilia and establishes IgH-2 cells as a suitable model system with which to investigate the phenomenon of caspase dependent apoptosis and the apoptotic machinery in a reptilian model.