The sarco-endoplasmic reticulum Ca 2؉ -transport ATPase (SERCA) loads intracellular releasable Ca 2؉ stores by transporting cytosolic Ca 2؉ into the endoplasmic (ER) or sarcoplasmic reticulum (SR). We characterized the only SERCA homologue of the nematode Caenorhabditis elegans, which is encoded by the sca-1 gene. The sca-1 transcript is alternatively spliced in a similar mode as the vertebrate SERCA2 transcript, giving rise to two protein variants: CeSERCAa and CeSERCAb. These proteins showed structural and functional conservation to the vertebrate SERCA2a/b proteins. The CeSERCAs were primarily expressed in contractile tissues. Loss of CeSERCA through gene ablation or RNA interference resulted in contractile dysfunctioning and in early larval or embryonic lethality, respectively. Similar defects could be induced pharmacologically using the SERCA-specific inhibitor thapsigargin, which bound CeSERCA at a conserved site. The conservation of SERCA2 homologues in C. elegans will allow genetic and chemical suppressor analyses to identify promising drug targets and lead molecules for treatment of SERCA-related diseases such as heart disease.

tbstract In this study, we have established that FtsY, the E. coil homolog of the mammalian signal recognition particle (SRP) receptor, is a GTP-binding protein which displays intrinsic GTPase activity. GTP was found to influence the protease sensil ivity of FtsY indicative of a conformational change. FtsY mutated in the 4th GTP-binding consensus element displayed reduced GTP-binding and -hydrolysis which correlated with a reduced ability to interact with SRP. Overexpression of the mutant proteins had a stronger inhibitory effect on protein translocation than overexpression of wild-type FtsY. These observations sugzest that in E. coli GTP is important for proper functioning of ~tsY in protein-targeting.

Autosomal dominant polycystic kidney disease (ADPKD) is a very common inherited disease caused by mutations in PKD1 or PKD2 genes characterized by progressive enlargement of fluid-filled cysts and loss of renal function [1]. Previous studies proposed a role for human polycystin-1 in renal morphogenesis acting as a matrix receptor in focal adhesions and for polycystin-2 as a putative calcium channel [2, 3]. The genome of Caenorhabditis elegans contains 2 new members of the polycystin family: lov-1, the homolog for PKD1; and pkd-2, the homolog for PKD2 [4; this paper]. Mutation analysis in C. elegans showed similarly compromised male mating behaviors in all single and double lov-1 and pkd-2 mutants, indicating their participation in a single genetic pathway. Expression analysis localized LOV-1 and PKD-2 to the ends of sensory neurons in male tails and to the tips of CEM neurons in the head, consistent with functions as chemo- or mechanosensors. Human and C. elegans PKD1 and PKD2 homologs, transfected into mammalian renal epithelial cells, co-localized with paxillin in focal adhesions suggesting function in a single biological pathway. Based on the role of polycystins in C. elegans sensory neuron function and the conservation of PKD pathways we suggest that polycystins act as sensors of the extracellular environment, initiating, via focal adhesion assembly, intracellular transduction events in neuronal or morphogenetic processes.

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