Meeting Abstract

P3.110  Jan. 6  Characterization of a C.elegans Orai1 homolog and its role in store-operated Ca²⁺ entry LORIN-NEBEL, C.**; YAN, X.; STRANGE, K.; Vanderbilt University, Nashville; Vanderbilt University, Nashville; Vanderbilt University, Nashville catherine.lorin-nebel@Vanderbilt.edu

Depletion of Ca²⁺ from endoplasmic reticulum (ER) stores activates plasma membrane Ca²⁺ influx, a process termed store-operated Ca²⁺ entry (SOCE). SOCE is believed to be an important mechanism for Ca²⁺ influx in numerous non-excitable cell types. Several recent studies have shown that two proteins, Stim1 and Orai1, play essential roles in SOCE. Orai1 likely encodes a store-operated Ca²⁺ channel and Stim1 functions as an ER Ca²⁺ sensor. We cloned a full-length C.elegans cDNA that encodes a 293 amino acid protein with 34-37 % sequence identity to human Orai1-3. GFP reporters demonstrated that C.elegans orai-1 is expressed in or close to the plasma membrane of the intestine, spermatheca, gonad sheath cells and hypodermis. C. elegans stim-1 shows an overlapping expression pattern and appears to be localized primarily to an intracellular compartment. Knockdown of orai-1 or stim-1 expression by RNA interference (RNAi) causes sterility due to loss of sheath cell and spermatheca contractile activity required for ovulation. Transgenic worms expressing a Stim1 mutant that constitutively activates SOCE in Drosophila and mammalian cells are sterile and exhibit severe posterior body wall muscle contraction (pBoc) arrhythmia. orai-1 RNAi suppresses the pBoc arrhythmia indicating that orai-1 and stim-1 function in a common pathway. Co-expression of orai-1 and stim-1 in HEK cells increases store-operated Ca²⁺ currents >100-fold. These results demonstrate that the molecular basis of SOCE is conserved in organism from worms to humans. Combining powerful forward and reverse genetic analyses with direct physiological measurements in C. elegans will likely provide unique insights into physiological and pathophysiological functions of SOCE and the molecular mechanisms of SOCE channel regulation.