Meeting Abstract

P1.122  Friday, Jan. 4  The mechanism of blastula expansion in sand dollars VON DASSOW, M; Duke Univ. Marine Lab mvondass@gmail.com

Because of its simple geometry, blastula expansion in echinoids provides an ideal model system for studying how biomechanics mediates interactions between environment and development. To realize this potential, we need to know the mechanism of blastula expansion. One model proposes that the osmotic pressure of the blastocoel fluid drives expansion. Another model suggests that blastula expansion is due to the geometric constraints of packing dividing cells into a single layer. To test these hypotheses, sand dollar (Dendraster excentricus) embryos were allowed to develop in solutions containing polymers (20 kD polyethylene glycol or 148 kD dextran) which osmotically squeeze the embryo since they cannot penetrate the fertilization envelope surrounding the embryo. The expansion of the cell layer, expansion of the extracellular matrix, and recovery after squeezing were investigated. Preliminary results suggest that osmotic squeezing causes the embryo to buckle and collapse, rather than shrink uniformly. This indicates that the cell layer continues to expand as the embryo is squeezed from the outside. This early result suggests that the expansion of the cell layer is not driven by swelling of the blastocoel, but by the dividing cells maintaining themselves in a single layer. Interestingly, this result contrasts with results seen in other echinoids, suggesting that different mechanisms may drive blastula expansion in different species. These different mechanisms could affect their responses to salinity variation.