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Comments on Fang Xie et al. (2003) International Worm Meeting "ced-7 Might Be Involved in ced-3-Independent Programmed Cell Death." (0)
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Fang Xie, & Bob Horvitz (2003). ced-7 Might Be Involved in ced-3-Independent Programmed Cell Death presented in International Worm Meeting. Unpublished information; cite only with author permission.
ced-3 encodes a member of the caspase family of cysteine proteases and is essential for almost all programmed cell death in C. elegans. However, a quantitatively low level of programmed cell death still appears to occur in the absence of CED-3 protease function. Such ced-3-independent cell death is indicated by the presence of unengulfed cell corpses in heads of L1 larvae containing strong loss-of-function mutations in both ced-3 and ced-1. (ced-1 is necessary for cell-corpse engulfment.) To investigate if any known cell-death genes are involved in this ced-3-independent death, we are examining whether mutations in other ced genes affect the number of corpses in ced-1; ced-3 animals. To date, we have observed that loss-of-function mutations in ced-7, and possibly in ced-9 and ced-4, decrease the number of corpses in heads of L1 triple mutants. Thus, these genes might play a role in ced-3-independent killing.In addition to CED-3, CED-4S, one of the two alternatively spliced ced-4 products, also has killing activity. By overexpressing CED-4S in ced-1; ced-3 animals, we observed that CED-4S can induce cell death in the absence of CED-3. Overexpression of another cell death activator, EGL-1, however, cannot induce cell death in a ced-1; ced-3 background.We are now using electron microscopy and Annexin V and TUNEL (TdT-mediated dUTP digoxgenin Nick End Labeling) staining to better characterize ced-3-independent cell death. Annexin V specifically labels apoptotic cells by binding to phosphatidylserine exposed on cell surface, while TUNEL labels free DNA ends in apoptotic cells. We are also examining if the caspase homologs csp-1, csp-2 and csp-3 are involved in ced-3-independent cell death.