Gastrulation Models Gastrulation has been celled "the most important time of your life" (Lewis Wolpert); without it you would be flat like a pancake! Vertebrate gastrulation is the process by which the simple structure of the blastula is transformed into the complex, 3-dimensional structure of the basic body plan by a series of cell shape changes and rearrangements. Due to basic differences in the construction of the early embryos (e.g. amount of yolk), the movements of gastrulation are dramatically different in different orders of animals. The movements of gastrulation have been visualized by staining small regions of the surface. The stained groups of cells were followed, originally manually and recently using time-lapse microscopy. The cells of the blastula can be divided into three groups according to which of the three germ layers they will become. The cells that remain on the outside will give rise to the ectoderm. The cells that end up in the middle to form the gut tube and associated organs are known as the endoderm. The cells that end up in between are the mesoderm. Each group is to construct 4 models depicting sequential stages of amphibian gastrulation using the colored clay that is available. Use the handouts and figures in your text as guides. In keeping with the conventions of developmental biology, use specific colors to represent the different layers and structures as follows: Blue - Ectoderm Red - Mesoderm Yellow - Endoderm Use green to represent neural ectoderm and white for the spaces (blastocoel and archenteron) or yolk. Once the clay models are done, use a wire to cut a saggital section (cut running along the anterior-posterior axis, dividing the embryo into left and right halves) or a transverse section (across the A-P axis). Compare to the figures for accuracy and to each other to examine how structures have moved during gastrulation. Locate the blastopore lip, the blastocoel and the three germ layers. How have the relationships between these changed over time?