During Caenorhabditis elegans development, exactly 131 somatic cells undergo apoptosis, their corpses being engulfed by neighbouring cells. This phenomenon provides a powerful tool to study phagocytosis as mutants that are unable to engulf cell corpses (ced mutants) are readily identifiable. So far, six separate genes required for engulfment have been identified and assigned to two, partially redundant, signal pathways; ced-2, ced-5 and ced-10 in one, ced-1, ced-6 and ced-7 in the other. With five of the six genes cloned, the identification of CED-1 by Zhou et al.1xCED-1 is a transmembrane receptor that mediates cell corpse engulfment in C. elegans. Zhou, Z et al. Cell. 2001; 104: 43–56Abstract | Full Text | Full Text PDF | PubMed | Scopus (311)See all References1 completes the list – at least for now.CED-1 is a transmembrane receptor that binds to cell corpses through its extracellular domain. Intriguingly, this binding requires the function of CED-7, a protein previously shown to resemble an ATP-binding cassette (ABC) transporter and encoded by the only ced gene that functions both in dying and in engulfing cells. The function of CED-7 remains unknown, although the authors suggest that it might present a cell-corpse ligand to CED-1.However, the intracellular domain of CED-1, which shows no overall homology to other proteins but contains an NPXY and a YXXL motif, is perhaps its most fascinating feature. Both motifs are necessary for the function of CED-1 and are partially redundant with each other. NPXY motifs bind to phosphotyrosine-binding (PTB) domains. As CED-6 contains a PTB, and is in the same functional group as CED-1, it is possible that CED-6 relays signals from CED-1, although the authors have so far failed to detect binding between the two proteins. YXXL motifs are phosphorylation sites for tyrosine kinases and are found in mammalian Fcγ-receptors, which mediate engulfment of IgG-coated particles.CED-1 is a fascinating evolutionary link – a single molecule that combines motifs found in separate proteins in higher organisms. Now the question is: how does it work?