Download Gastrulation and Neurulation Lecture Key points Frog gastrulation is

Gastrulation and Neurulation Lecture Key points Frog gastrulation is more complex but involves the same cell behaviors—changes in adhesion, apical constriction, and convergent elongation. Experiments allowed us to determine what events (maternal set up of the animal/vegetal axis plus sperm entry) determined the location of the blastopore. Large yolk volume or need to build placental connection to mother further complicate topology of chick or mammalian gastrulation Fly dorsal-­‐ventral patterning allows us to dissect how sequential cell-­‐cell signaling events drive cell fate choices and also drive cell behavior-­‐ in this case apical constriction of the mesoderm Vertebrate neural tube formation involves similar cell machinery to drive apical constriction These events define the three germlayers—ectoderm, endoderm and mesoderm—and the tissues that arise from them In summary, conserved cell shape and cell adhesive changes drive cell movements in shaping all early embryos SAMPLE Learning objectives After this lecture you should be able to: Compare frog gastrulation to that of the sea urchin, pointing out similarities in cell shape change and their cell biological bases, and differences in 3-­‐dimensional movements Summarize the experiments that led to our model for how sperm entry positions the blastopore Contrast in outline chicken and mammalian gastrulation (we cover these in less detail) with that in frogs, and explain the major reasons for the differences Outline the mechanisms by which cell fate decisions are translated into cell shape change, using fruit fly mesoderm as an example Describe the derivatives of the three germ layers Contrast the behavior of cells during neurulation with that of earlier events in gastrulation in terms of cell shape change and cytoskeletal involvement Guided Reading Q’s Read pages 243-­‐248 (Top), Fig 7.10, and 250-­‐251 (Sidelights…), and answer the following questions about events in Xenopus. 1) How is the cell organization of the Xenopus blastula similar to and different from that of the sea urchin? 2) What ratio determines the timing of the mid-­‐blastula transition and how might this occur in molecular terms? 3) What cell shape occurs in the bottle cells and how does this fit into gastrulation? 4) Xenopus gastrulation also involves convergent extension—however, in this case it adds a third dimension—
how does this lead to a one cell thick IMZ?. 5) Describe in your own words the experiment that revealed a role for fibronectin in gastrulation. What proteins form the receptor for fibronectin?. Read pages 305-­‐307 and answer the following questions on mammlian gastrulation. 6) In mammals, which occurs first—gastrulation or initiation of formation of extraembryonic membranes. 7) What cell behavior is exhibited by cells of the primitive groove? Read pages 211-­‐215 and answer the following questions about events in Drosophila gastrulation. 8) The initial cue to set up dorsal-­‐ventral cell fates occurs by signaling between the oocyte and the somatic follicle cells that build the eggshell. What cell signals and what cell receives signals? Which gene encodes the ligand and which the receptor? 9) The next step is signaling from the eggshell protein Spätzle and the oocyte—the side of the embryo that receives the Spätzle will become the dorsal / ventral side. 10) What type of protein does the dorsal gene encode—i.e., what is its job within a cell? 11) Cells that have the highest level of nuclear dorsal become which germ layer (ectoderm, endoderm, or mesoderm)? What transcription factor do they express and what cell shape change do they initiate? Read Figures 9.4, 9.5, and 9.6 and answer the following questions about neurulation 12) What cytoskeletal element would drive the apical constriction of cells in the neural hinge? 13) If the neural tube fails to close anteriorly in humans, this causes ________________ 14) Which cadherin is expressed by cells of the invaginating neural tube?