Meeting Abstract
Cell adhesion is a key feature of the multicellular ancestor that was definitive for the origin of Metazoa. Although many of the major cell adhesion systems are ubiquitous and their components were present in the metazoan unicellular ancestors, little is known when and how some of these proteins started to form functional adhesion complexes and/or co-opted to their current functions. The vinculin family of proteins is key to cell-to-cell and cell-to-ECM adhesion complexes. This family includes α-catenin and vinculins, which are well studied in model bilaterian systems, where they regulate actin-based structures, including cadherin- and integrin-based cell adhesions. However, we know nothing about their function in non-bilaterian animals, such as sponges, which could offer a valuable insight into the evolutionary history of these proteins. Here, we examine the function and tissue/subcellular localization of two vinculin-family proteins in the freshwater sponge Ephydatia muelleri. For Vin-1 (a homolog of vinculin), we found evidence for two different cellular populations that function in adherens junctions (cadherin-based cell adhesion) and focal adhesions (integrin based adhesions); these data represent the first experimental molecular evidence for the presence of cell junctions in sponge tissues. In contrast, Vin-2 (an uncharacterized Vin family protein present in all animal clades except vertebrates) was found to localize to the microtubule organizing center (MTOC). Taking into account that choanoflagellates only have one vinculin homolog, which also localizes to the MTOC, these data suggest that genome duplications in the metazoan stem-lineage led to the origin of vinculin and alpha-catenin from a Vin-2-like ancestral protein, which functioned at the MTOC.
