The Caenorhabditis elegans Ldb/NLI/Clim orthologue ldb-1 is required for neuronal function

LIM homeodomain (LIM-HD) and nuclear LIM-only proteins play important roles in a variety of developmental processes in animals. In some cases their ac tivities are modulated by a nuclear LIM binding protein family called Ldb/N LI/Clim. Here we characterize the Ldb/NLI/Clim orthologue ldb-1 of the nema tode Caenorhabditis elegans. Two alternatively spliced variants exist, whic h differ in their amino-termini. The ldb-1 orthologue of Caenorhabditis bri ggsae has the same structure as that of C. elegans and is highly conserved throughout the open reading frame, while conservation to ny and vertebrate proteins is restricted to specific domains: the dimerization domain, the nu clear localization sequence, and the LIM interaction domain. C. elegans ldb -1 is expressed in neurogenic tissues in embryos, in all neurons in larval and adult stages, and in vulval cells, gonadal sheath cells, and some body muscle cells. C. elegans LDB-1 is able to specifically bind LIM domains in yeast two-hybrid assays. RNA inactivation studies suggest that C. elegans l db-1 is not required for the differentiation of neurons that express the re spective LIM-HD genes or for LIM-HD gene autoregulation. In contrast, ldb-1 is necessary for several neuronal functions mediated by LIM-HD proteins, i ncluding the transcriptional activation of mec-2 the mechanosensory neuron- specific stomatin. (C) 2000 Academic Press.