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 activities are modulated by a nuclear LIM binding protein family called Ldb/NLI/Clim. Here we characterize the Ldb/NLI/Clim orthologue ldb-1 of the nematode Caenorhabditis elegans. Two alternatively spliced variants exist, which differ in their amino-termini. The ldb-1 orthologue of Caenorhabditis briggsae has the same structure as that of C. elegans and is highly conserved throughout the open reading frame, while conservation to fly and vertebrate proteins is restricted to specific domains: the dimerization domain, the nuclear 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 ldb-1 is not required for the differentiation of neurons that express the respective LIM-HD genes or for LIM-HD gene autoregulation. In contrast, ldb-1 is necessary for several neuronal functions mediated by LIM-HD proteins, including the transcriptional activation of mec-2, the mechanosensory neuron-specific stomatin.