The asymmetrical distribution of phosphatidylserine (PS) across plasma membrane is disrupted in apoptotic cells, which leads to the exposure of PS on the cell surface that serves as an "eat-me" signal for their clearance. How PS asymmetry is maintained and regulated during apoptosis and in other cellular processes is poorly understood. From a genetic screen for regulators of engulfment signal, we isolated several alleles of
tat-1 (transbilayer amphipath transporters) and one allele of
res-1 (regulator of engulfment signals).
tat-1 encodes a P-type ATPase that is suggested to promote the inward movement of aminophospholipids such as PS and PE, which restricts them to the inner leaflet of cell membrane. Consistent with previous findings (1), we found that in the
tat-1 mutants, the surface-exposed PS is detected not only on apoptotic cells, but also on living cells. Identical phenotypes were also observed in the
res-1(
qx36) mutants, indicating that
res-1 is also involved in maintaining PS asymmetry on plasma membrane. Interestingly, we found that both
tat-1 and
res-1 mutants display severe defects in membrane trafficking including intestinal vacuolation and endocytosis defects in both intestine and coelomocytes. TAT-1 is localized to plasma membrane and intracellular vesicles, which is consistent with its function in maintaining PS asymmetry across cell membrane and in endocytosis (1, 2). Importantly, the membranous and vesicular localization of TAT-1 is totally disrupted in the
res-1(
qx36) mutants. On the other hand, RES-1::GFP showed similar localization pattern to that of TAT-1, which is abolished in the
tat-1(
qx30) mutants. Therefore, RES-1 and TAT-1 likely cooperates with each other to regulate PS asymmetry and membrane trafficking in C. elegans. We will report our characterizations of RES-1 and TAT-1 in the meeting. 1.Monica Darland-Ransom, Xiaochen Wang, Chun-Ling Sun, James Mapes, Keiko Gengyo-Ando, Shohei Mitani, Ding Xue, 2008. Role of C. elegans TAT-1 protein in maintaining plasma membrane phosphatidylserine asymmetry. Science 320: 528-531 2.Anne-Francoise Ruaud, Lars Nilssoon, Fabrice Richard, Morten Krog Larsen, Jen-Louis Bessereau and Simon Tuck, 2009. The C. elegans P4-ATPase TAT-1 regulates lysosome biogenesis and endocytosis. Traffic 10(1): 88-100.