Fig. 5. A model for CED-9 function in mitochondrial homeostasis. In C. elegans, CED-9 does not appear to be essential for mitochondrial homeostasis. Mitochondrial fusion, which probably involves the mitofusin FZO-1, can occur in the absence of CED-9. Similarly, mitochondrial fission, which involves DRP-1 can also occur in the absence of CED-9. This and other studies (Delivani et al., 2006; Jagasia et al., 2005), however, suggest that CED-9 may play a role in potentiating the activities of both DRP-1 and FZO-1. Additionally, CED-9 may itself be regulated by the mitochondrial fission protein DRP-1. If true, regulation of CED-9 by DRP-1 would provide a mechanism for cross-regulation between the mitochondrial fission and fusion machineries. Such a pathway would allow DRP-1 to promote mitochondrial fission both directly, and through downregulation of FZO-1 by way of inhibiting CED-9.