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 and result in persistent cell corpses. We have cloned both
ced-5 and
ced-7 by transformation rescue. Six stretches of amino acid sequence across CED-5 are homologous to those of a yeast gene of unknown function identified by the Yeast genome sequencing project.
ced-5, like the engulfment genes
ced-2 and
ced-10, is required for the engulfment of cell corpses as well as for proper distal tip cell (DTC) migration. Five of six
ced-5 alleles isolated affect both processes. The sixth allele
n2002 has the same number of persistent corpses as the null allele
n1812, but has almost no DTC migration defect. The
n2002 allele has a nonsense mutation, presumably deleting the C-terminal half of the CED-5 protein. This result suggests that the truncated CED-5 protein may be sufficient to function in DTC migration but not in the engulfment of cell corpses. We raised antibodies against the C-terminal half of the CED-5 protein. On western blots, CED-5 antibodies detected an ~180 kD protein in N2 but not in the
ced-5 mutants
n2002 or
n2691. The same band was also detected in
ced-3,
ced-4 and
ced-9(gf) mutant embryos, in which programmed cell deaths are blocked. This result implies that CED-5 expression does not require the process of cell death.
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 has two similar halves, each with six transmembrane domains and an ATP binding site. By introducing mutations into either ATPbinding site, we found that the N-terminal site plays a more important functional role in engulfment of cell corpses than does the C-terminal site. CED-7 antibodies recognized an ~170 kD protein in N2 but not in the
ced-7 mutants
nl997 or
n2094. In wild-type embryos, CED-7 antibodies stained the plasma membrane of most or all cells. In wild-type larvae and adults, CED-7 antibodies stained germline precursors or germline respectively and more faintly stained a few unidentified cells in the head and the tail. The same staining pattern was detected in engulfment mutants (
ced-1,
ced-2,
ced-5,
ced-6 and
ced-10), suggesting that none of these genes regulates CED-7 expression or localization. We are currently attempting to determine if
ced-5 and
ced-7 function in the dying cells or in the engulfing cells.