After cells undergo programmed cell death, their corpses are engulfed by neighboring cells. Mutations in
ced-5 and
ced-7 prevent dying cells from being engulfed, resulting in persistent cell corpses. We have cloned
ced-5 and
ced-7 by transformation rescue. The sequence of 5.5 kb from overlapping
ced-5 cDNAs suggests that
ced-5 encodes a novel protein. An ~5.6 kb transcript is detected on northern blots, suggesting that our cDNA sequence is very close to full length. On western blots, CED-5 antibodies detect an ~180 kD protein in N2 but not in the
ced-5 mutants
n2002 or
n2691. The same band is also detected in
ced-3,
ced-4,
ced-8 and
ced-9(gf) mutants in which programmed cell deaths are blocked. This result implies that CED-5 expression does not require the process of cell death. The expression of CED-5 also is not altered in other engulfment mutants (
ced-1,
ced-2,
ced-6,
ced-7,
ced-10), suggesting that none of these genes regulates CED-5 expression.
ced-7 encodes a protein similar to ABC (ATP-Binding Cassette) transporters. The CED-7 protein is predicted to be 191 kD in size and appears to have two similar halves, each with several transmembrane domains and an ATP-binding site. So far, we have identified molecular lesions in six
ced-7 alleles. Five alleles have nonsense mutations and exhibit about the same number of persistent corpses in the head of newly hatched animals. The sixth mutant has a mutation in a splicing consensus sequence and is the weakest allele. An antibody against the C-terminal half of CED-7 protein recognizes an ~170 kD protein in N2 but not in the
ced-7 mutant
n1997. To determine whether
ced-5 and
ced-7 are expressed and function in the engulfed cells or in the engulfing cells, we are currently determining their expression patterns using antibodies and performing mosaic analyses.