In the development of multicellular organisms, the proper removal of cell corpses generated by programmed cell death prevents the possible dispersal of harmful cellular contents from dying cells. A recent study has shown that
psr-1 , the C. elegans homolog of human PSR (phosphatidylserine receptor), is important for cell-corpse engulfment (Wang et al., 2003). PSR-1 is proposed to function as a receptor and act upstream of the pathway mediated by CED-2, CED-5, CED-10, and CED-12 signaling molecules, possibly through physical interactions with CED-5 and CED-12 to control the engulfment process. In order to understand how PSR-1 interacts with CED-5 and CED-12, we mapped the binding region in PSR-1 for CED-5 and CED-12 interactions. We found that the amino acids 135-257 are required but not sufficient for CED-5 binding and the amino acids 212-257 of PSR-1 are required and sufficient for CED-12 binding. In addition, PSR-1 is predicted to have one tyrosine phosphorylation site. To investigate its function in cell-corpse engulfment we changed the tyrosine to phenylalanine in PSR-1 and found that the mutant PSR-1 failed to rescue the cell-corpse engulfment defect in
psr-1 mutants. Therefore, the tyrosine residue and possibly its phosphorylation is important for PSR-1 function. To explore the expression pattern of PSR-1, we generated polyclonal antibodies against GST-PSR-1 fusion protein. We are currently investigating the subcellular localization of PSR-1. Reference: Wang, X., Wu, Y., Fadok, V.A, Lee, M., Gengyo-Ando. K., Cheng, L., Ledwich, D., Hsu, P., Chen, J., Chou, B., Henson, P., Mitani, S., Xue, D. Science 302, 1563-1566 (2003).