Meeting Abstract
Understanding the evolution and ancestral functions of cell-cell adhesion proteins promises to shed light on how animal multicellularity evolved, and how the first animal tissues were assembled. Here, we examined the function of &alpha-catenin/vinculin-related proteins (Vin-family proteins) in choanoflagellates and sponges. Two questions of particular interest are 1) how do Vin-family proteins function in the colonial life stages of choanoflagellates? And 2) how do Vin-family proteins function in the choanoderm tissue (the feeding epithelium) of sponges, which has long been hypothesized to be an ancient animal tissue type based upon its cytological similarities with choanoflagellates? In bilaterians, Vin-family proteins function to regulate actin-based structures, including cadherin- and integrin-based cell adhesions. Our results point to a novel role for a choanoflagellate Vin-family protein that is unrelated to either actin regulation or colony formation. Instead, we find evidence for a discrete cellular population adjacent to the nucleus, a pattern consistent with a role at the centrosome. In sponges, we examine a putative vinculin ortholog (Vin1) and find evidence for at least three different cellular populations that function in adherens junctions (cadherin-based cell adhesion), focal adhesions (integrin based adhesions), and co-localized with actin at roots of microvilli in the choanoderm. These data contribute to a new hypothesis about how Vin-family proteins may have functioned in an ancestral, unicellular context, and provide a new, structural context for understanding the evolutionary links between sponge and bilaterian tissues.
