Phagocytosis of apoptotic cells is a tightly controlled cellular process regulated by pathways highly conserved from the nematode C.elegans to humans. The best-characterized feature that distinguishes dying cells from normal cells is the exposure of phosphatidylserine (PS), which serves as a general eat me signal for the removal of apoptotic cells. How PS is exposed and recognized is still elusive. Our previous study identified
psr-1, the C. elegans phosphatidylserine receptor (PSR-1), as a potential upstream receptor that recognizes exposed PS and transduces the engulfment signal through
ced-2/ced-5/ced-10/ced-12 signaling pathway (1). PSR-1 is unlikely the only engulfment receptor in this pathway because the
psr-1 deletion mutant (
tm469) displays much weaker engulfment defect than that of the
ced-2,
ced-5,
ced-10 or
ced-12 mutants. In order to identify other engulfment receptors or components that function redundantly with
psr-1, an enhancer screen was performed to search for mutations that enhance the engulfment defect of the
psr-1(
tm469) mutant. From a screen of 3600 haploid genomes, we identified two new genes, which are named pens (
psr-1 enhancers) genes. Here we report genetic and phenotypic characterization of
pens-1 and
pens-2. Examination of
pens-1 (
sm211) and
pens-2 (
sm237) mutant embryos reveals that significantly higher numbers of cell corpses were accumulated in
pens-1(
sm211) or
pens-2(
sm237) embryos than in wild type embryos at all embryonic stages. This increase of embryonic cell corpses in
pens-1 and
pens-2 animals is not dependent on the
psr-1(
tm469) mutation and does not appear to be due to a defect in the cell death activation process. Double mutants among
pens-1,
pens-2 and other engulfment genes (
ced-1,
ced-6,
ced-7 and
ced-2,
ced-5,
ced-10,
ced-12) are being constructed. We are also in the process of mapping and cloning these two genes. Genetic characterization and molecular cloning of
pens-1 and
pens-2 will facilitate our understanding of how these two genes may function to affect the cell corpse engulfment process in C. elegans. 1. Wang, X.C., Wu, Y.C., Fadok, V., Lee, M.C., Gengyo-Ando, K., Cheng, L.C., Ledwich, D., Hsu, P.K., Chen, J.Y., Chou, B.K., Henson, P., Mitani, S., and Xue, D. (2003). Cell Corpse Engulfment Mediated by C. elegans Phosphatidylserine Receptor Through CED-5 and CED-12. Science 302, 1563-1566.