51.4 Thursday, Jan. 5 Blastomere deletions reveal organizing activity in the polychaete annelid Capitella teleta AMIEL, Aldine; HENRY, Jonathan Q.; SEAVER, Elaine C.*; University of Hawaii; University of Illinios; University of Hawaii email@example.com
The formation of a transient structure in the embryo called the organizer is crucial for establishment of the body axes. The vertebrate organizer is a specialized group of cells that orchestrates the formation of entire animal via cell-cell signaling and morphogenetic movements during gastrulation. In spiralian animals, organizing activity is localized to 1 -2 cells in the early cleavage stage embryo, namely 3D in the mollusks L. obsoleta and C. fornicata, and 2d plus 4d in the oligochaete annelid T. tubifex. The purpose of the present study is to investigate whether a similar organizing activity is found in the polychaete annelid Capitella teleta, a model well-suited for embryological approaches. The identity of organizer activity has not been characterized in polychaetes. The stereotypic spiralian cleavage program in Capitella and its known cell lineage allows for identification of each cell and its resulting larval fate. Over 12 uniquely identifiable individual blastomeres were ablated in Capitella using a laser ablation system and resulting larval phenotypes analyzed. For many of the blastomere ablations, resulting larvae lacked structures that normally arise from the ablated cell, but were otherwise normal. Our results show that organizer activity in Capitella arises from a cell in the D quadrant, although not the same cell as in molluscs (3D), and its activity occurs at an earlier stage of development. Furthermore, only the D/V axis is disrupted following D quadrant cell ablations. These results highlight variation among spiralians, and may ultimately give insight into how changes in the highly conserved spiralian developmental program generate the enormous diversity of body plans in the Lophotrochozoa.