Recently, proteins from a new family of neuron-specific EF-hand calcium binding proteins have been described. Members of this family are highly conserved through evolution. These proteins are though to be calcium sensors/modulators and upon Ca2+ binding should interact with target proteins and alter their activity. They are found mainly in neurons and are likely to be involved in the fine-tuning of calcium-dependent processes in the nervous system. This emerging branch of the superfamily of EF-hand calcium binding proteins forms the growing family of Neuron specific Calcium Sensors (NCS) often called the recoverin or the vilip family. In the chick brain, we have been able to isolate a novel member of the NCS family that we named NCS-1. We have also characterized its ortholog in the rat which has 100% of amino acid identity. To study the function of NCS-1, we decided to use the C. elegans system. Therefore, we first cloned the NCS-1 homolog in C. elegans that was named Ce-NCS-1 [localization X: -18.85; cDNA: genbank name CELNCS1, accession L33680; Protein: Swiss Prot name NCS1_CAEEL, accession
p36608]. This protein has 75% of amino acid identity with rat/chick NCS-1. NCS-1 is also the only NCS protein that as an homolog in yeast (with, ~62% for S. Cerevisiae and ~70% for S. Pombe, amino acid identity with the rat/chick NCS-1). Therefore NCS-1 is so far the most conserved member of the NCS family. (We also characterized an other C. elegans NCS protein: Ce-NCS-2 [localization I:4.46; cDNA: genbank name CELNCS2, accession L33681; Protein: Swiss Prot name NCS2_CAEEL, accession
p36609] which possesses only 45% of amino acid identity with Ce-NCS-1 and rat/chick NCS-1). In order to localize the expression of Ce-NCS-1 we have produced transgenic worms harboring a
ncs1-promotor::GFP construct, generated antibodies against the purified recombinant Ce-NCS-1 and performed immunolocalization. To get insight into the in vivo function of Ce-NCS-1 we have also isolated a Tc1 deletion derivative mutant with the
ncs1 gene deleted. From both immunofluorescence (IF) and GFP data, Ce-NCS-1 appears to be expressed mainly in sensory neurons. We observe staining in 10 sensory neurons, 2 inter-neurons and in 1 motor-neuron as well as in a pharyngeal muscle cell. On the IF only, there is also staining in the vulva muscles and in the anal depressor muscle. We are currently testing the
ncs1 mutant for chemosensory defects. This mutant seems to have a lower chemotaxis index for some volatile attractants. We are now testing chemosensory adaptation as well as threshold sensibility. This mutant should also be tested for egg-laying and defecation defects.