Meeting Abstract
56.5 Jan. 6 &beta-catenin mediated binary specification in the spiral-cleaving polychaete Platynereis dumerilii SCHNEIDER, Stephan Q.*; BOWERMAN, Bruce; Univ. of Oregon, Eugene; Univ. of Oregon, Eugene schneider@molbio.uoregon.edu
&beta-catenin functions in the canonical Wnt-signaling pathway by activating target gene expression in the nucleus. Early roles for &beta-catenin signaling are surprisingly different among animal phyla. To gain insight into the ancestral role of &beta-catenin, we are using the polychaete Platynereis dumerilii. Platynereis embryos deploy a highly stereotypic cell division program called spiral cleavage that generates blastomeres of defined size and cell fate, in a series of animal-vegetal (a-v) oriented cell divisions. We observed a-v asymmetries in the levels of detectable &beta-catenin during embryonic cell divisions, from fertilization through the spiral cleavage stages and up to and beyond the emergence of bilateral symmetry. In each of these a-v oriented cell divisions nuclear &beta-catenin levels are increased in vegetal daughter cells and decreased in animal daughter cells. This asymmetry occurs independent of cell size, cell cycle, cell fate, and cell lineage. Interestingly, the asymmetry is lost only in transverse/bilateral cell divisions, and is reversed during the segregation of germ cell lineages. Furthermore, we demonstrate that treatment with GSK3 inhibitors causes nuclear accumulation of &beta-catenin in animal daughter cells and results in animal to vegetal cell fate transformations. These results are strikingly reminiscent of the anterior-posterior oriented divisions, Wnt pathway asymmetries and functions that occur throughout embryogenesis in C.elegans. We also find similarities to &beta-catenin signaling in early deuterostome and insect embryos. We propose that this a-v asymmetry of &beta-catenin in daughter cells constitutes an ancestral and versatile binary specification mechanism that has been deployed and modified throughout evolution in metazoan embryos.
