| During gastrulation in the sea urchin embryo the archenteron, or primitive gut, is formed by an initial process of invagination at the vegetal pole of the embryo, followed by extension across the blastocoel toward the future mouth. Neither the genetic basis of gastrulation nor the detailed movement of the cells involved in archenteron formation is well understood. This thesis describes a new 4D imaging methodology by which embryonic lineage and gene regulatory states can be connected to cell behavior by tracking individual cells of the living embryo through developmental time. The work presented in this thesis shows directly the dramatic cellular rearrangement that comprises gastrulation. Furthermore, it shows that this rearrangement occurs in the veg2 lineage of cells expressing foxa, and not in the adjacent veg1 lineage of cells expressing brachyury. Very late in gastrulation some veg1 cells move in as a coherent truncated cone to produce the hindgut. However, veg1 cells located outside the vegetal ring of brachyury expression prior to gastrulation never contribute to the archenteron. |
