Sea Urchin Development - BIO361_SeaUrchin_7Oct24 PDF

 Holoblastic cleavage: Radial Meridion al Equatori al “3” Axes of symmetry* 1 Axis of symmetry Example: Sea urchin Figure 10.3 Micrographs of clea...

 Holoblastic cleavage: Radial Meridion al Equatori al “3” Axes of symmetry* 1 Axis of symmetry Example: Sea urchin Figure 10.3 Micrographs of cleavage in live embryos of the sea urchin Lytechinus variegatus, seen from the side Time-lapse imaging of sea urchin cleavage Cleavage will give rise to: Mesomeres Macromeres Micromeres  Holoblastic cleavage: Radial Meridion al Equatori al Biochemic ally isotropic Biochemic ally anisotropic Example: Sea urchin  Evidence that the 1-cell zygote is biochemically asymmetric 1-cell zygote “Maternal Determinants” Complete Animalization Maternal Determinant ABSENT Maternal Determinant PRESENT Cilia Permanent "blastula" of Maternal determinant ciliated epidermal cells present in vegetal pole formed by experimental of embryo ensures isolation of animal pole development of all cells of the sea urchin three germ layers embryo  What is the Maternal Determinant? Egg Dishevelled Rotate 90 o eitzel et al., 2004, Development What is the Function of Dishevelled? Answer: To Prevent Degradation of b-catenin (Canonical Pathway) LiCl  Is b-catenin Localized to Vegetal Cells? Dishevelled Cell outline b-catenin  Dishevelled and b-catenin Localize to the Micromere and Veg2 Cells Dishevelle d & b- catenin David McClay lab @ Duke University  Based on what we know, we can propose two hypotheses Dishevelle d & b- catenin Hypothesis 1: Stabilizing b-catenin everywhere should alter the fates of an1 and an2 cells. Hypothesis 2: Inhibiting b-catenin translocation to the nucleus should alter the fates of veg1 and veg2 cells. thesis 1: Stabilizing b-catenin everywhere should alter the fates of an1 and an2 LiCl LiCl Gsk3 b-catenin Results are similar to this experiment’s results Hypothesis 2: Preventing b-catenin from entering the nucleus should alter the fates of veg1 and veg2 cells. Results are similar to this experiment’s results  The micromeres (site of b-catenin expression) are SPECIAL! 64-cell stage 16 16 8 ∑ = 64 8 8 8 Autonomously specified  I. The Large Micromeres are Fated to Become Skeleton Pluteus Cheers and Ettensohn, 2005, Dev Bio Remove d/dx SkeletonCell fate is SPECIFIED Gene Regulatory Networks and Logic Gates: Double-negative gate Skeletogenic Fate of the Micromeres is Tied to the Maternal Determinant, b-cate X Bottom Line: b-catenin activates Pmar1 expression in micromeres. Pmar1 expression inhibits HesC. Without HesC, skeleton-forming genes are expressed. Figure 10.9 “Logic circuits” for gene expression Double-negative Feed-forward gate: A repressor circuit: A signal of a repressor amplification mechanism Notch Signaling What What type type of of signaling signaling is is this? this? Autocrine Autocrine Endocrine Endocrine Juxtacrine Juxtacrine Paracrine Paracrine II. The Large Micromeres have Inductive Potential  II. The Large Micromeres have Inductive Potential Transplant How do small/large micromeres redirect developmental pathway of animal hemisphere? How do small/large micromeres redirect developmental pathway of animal hemisphere? Egg Region where micromeres come from Dishevelled  II. The Large Micromeres have Inductive Potential …Animal cell fate is CONDITIONALLY SPECIFIED Transplant Non-neutral Environment …Micromere cell fate is AUTONOMOUSLY SPECIFIED  Gastrulation in Sea Urchin These cells are ingressing Figure 10.11 Ingression of skeletogenic mesenchyme cells Hyaline layer: A clear substrate, composed of the protein hyaline Recall that deuterostome cells in G and I phases all have LAMIN: Notice how it breaks down in (C). Note arrangement of ECM fibers parallel to direction of travel. Recall that mesenchymal cells preferential secrete collagen. Secretion of CSPG causes water absorption in the inner lamina, which in turn causes the lamina to expand and ‟push” cells in towards the blastocoel  Ingression of micromeres leads to loss of b-catenin expression Upon INGRESSION, micromeres become primary mesenchymal cells (PMC) PMCs aggregate at FGF sites of high b- PMCs migrate to catenin expression FGF FGF regions of FGF expression E-Cadherin b-catenin Mesenchymal marker. Note that Micromeres ingress: micromeres no Micromeres express FGF longer express b- receptors on their plasma catenin membrane. What type of receptor activity is present on Figure 10.12 Positioning of skeletogenic mesenchyme cells in the sea urchin (Part 3) From a signal transduction FGF perspective, what’s going on here? Where else have you seen a similar phenomenon involving the same signal transduction mechanism? FGF Receptor  The PMCs (now called skeletogenic mesenchyme) form a syncytium Syncytial cables Secretion of calcium carbonate leads to skeleton formation romeres  Primary Mesenchyme Cells (PMC)  Skeletogenic Mesenchyme  Skele Gastrulation in Sea Urchins Starts with Invagination Blastopore Formation is the Beginning of Gastrulation Blastopore  Gastrulation in Sea Urchin Archenteron (Primitive Gut) The archenteron is formed using cell shape changes, cell rearrangements, filopodial extensions, and convergent extension. Gastrulation forms the Archenteron (Primitive Gut) Filipodial extensions Recall that Lamellipodia and Filopodia are cytoskeletal structures found in mesenchymal cells. They localize towards the direction of movement. Figure 10.15 Extension of the archenteron in sea urchin embryos Figure 10.15 Extension of the archenteron in sea urchin embryos