Latrophilins: Synaptic proteins with a novel epithelial function in Caenorhabditis elegans, and the evolution and function of family B G-protein coupled receptors.

摘要

Latrophilins are cell surface proteins containing an extracellular cell adhesion/interaction domain joined to a serpentine family B G-protein coupled receptor (GPCR) signaling domain. In vertebrates, multiple alternatively spliced paralogs exist and are expressed in the nervous system with proposed synaptic localization. By using BLAST searches and sequence comparison, we identified two C. elegans orthologs, lat-1 and lat-2, that have similar overall protein structure, but unlike the vertebrate orthologs, are not highly alternatively spliced, with only lat-1 having two isoforms. Using lat-1 transcriptional and translational GFP reporters, we see lat-1 expression in two main cell types: developing epithelia and neurons, localizing to dynamic and potential presynaptic surfaces, respectively. RNAi and deletion mutants show defects in embryonic elongation, pharyngeal development and reproductive organ formation, correlating with the expression in the epithelium of these tissues. In comparison, lat-2 expression is limited to the arcade and g1 gland cells with expression cycling during molts. Our data suggests a role for lat-1 in the movement or attachment of developing epithelia, and role for lat-2 in molting.; Additionally, we have identified a total of eight family B GPCR genes in C. elegans: flamingo (fmi-1/F15B9.7), two latrophilin-related proteins (lat-1/B0457.1, lat-2/B0286.2), two methuselah-related proteins (mth-1/F31D5.5, mth-2/F31D5.4), and three presumptive hormone receptors ( seb-1/C13B9.4, seb-2/ZK643.4, seb-3/C18B12.2). We have characterized the coding mRNA and genomic structure by sequencing cDNAs and RT-PCR products, evolution by sequence and domain comparisons, and expression of these genes by promoter-GFP fusions. In addition, our analysis of the ongoing evolutionary processes of the family B GPCRs in C. elegans/C. briggsae and H. sapiens/ M. musculus indicates resistance to large scale changes in overall gene number and structure, and a tolerance to varied amount of change in the protein and DNA sequence. Our analysis of the evolution of this family indicates major alterations of domain structure and multiple duplication events prior to the metazoan radiation, leaving at least five orthologus branches between C. elegans and other present metazoan lineages.