BIO 131 Study Guide Chapter 43 Part Two PDF

Summary

This document is a study guide on sea urchin gastrulation, part of a larger chapter on the formation of germ layers in embryos. It details the process by which ectoderm, mesoderm and endoderm are created and the movement of cells in the sea urchin.

Full Transcript

Study guide chapter 43 part two Gastrulation - the process by which the three germ layers of the animal embryo are formed: ectoderm, mesoderm, and endoderm. Three Germ Layers formed during Gastrulation 1) Ectoderm – Outer layer (skin/nervous system) 2) Mesoderm – Middle layer (muscles and organs) 3)...

Study guide chapter 43 part two Gastrulation - the process by which the three germ layers of the animal embryo are formed: ectoderm, mesoderm, and endoderm. Three Germ Layers formed during Gastrulation 1) Ectoderm – Outer layer (skin/nervous system) 2) Mesoderm – Middle layer (muscles and organs) 3) Endoderm – innermost layer digestive and respiratory tract. - three model systems we used to examine gastrulation sea urchin, frog, chick Sea Urchin Gastrulation 1 - Blue : ectoderm precursor - Yellow: endoderm precursor - Red: Mesoderm precursor - Black: some type of micromeres??? (part of mesoderm???) [he calls them micromere descendents] - Image A: Blastomeres (pre-blastula formation) Color-coding based on different contents and have different sizes (micromeres/macromeres) but similar morphology Image B: Blastula formed Differentiation has occurred in the cells --- cell morphology has changed - no longer round and surface area has been molded such that the cells are more conducive to the attachment of cells --- Increased cell adhesion proteins (cells stick together along their membrane surface) and proteins involved in ion transport cells form cialis (hairlike structures) which are a sign that the cell has been differentiated Note color coordination Image C: The vegetal hemisphere (bottom half where mesoderm and endoderm precursors are located) gets flattened Sea Urchin Gastrulation 2 Image D: The mesoderm precursor cells begin to disassociate from the vegetal hemisphere and make their way into the blastocoel; these cells are now called the Primary mesenchyme cells see "Movement of Primary Mesenchyme cells" term [see Sea Urchin Gastrulation 2 for pics from here] Image E: The cytoskeletons of the micromere descendants (the black part) are drawn to the opposite end of the cell (the animal pole), which drives the entire vegetal pole upward in that direction The cells that eventually become the endoderm are pulled up with it and start to displace the blastocoel --- The inward push has formed a canal that is called the Archenteron, which eventually becomes the passageway used by the anus to dispel waste --- The Blastopore is the indentation at the very tip of the canal which becomes the anus in sea urchins As this indentation happens, additional mesenchyme cells are released called Secondary mesenchyme cells Image G: Mesoderm precursor cells divide and form long structures called skeletal rods that have contractile abilities which help in the movement of the sea urchin Part of the ectoderm (outer layer) begins to form an indentation called to Stomodeum that eventually forms an opening which becomes the mouth At this point we already see the beginning of the anus, gut, and mouth Image I: Distinct structures can be seen in the larval stage (called pluteus) --- anus where blastopore was --- mouth where stomodeum was --- skeletal rods circumvent the entire larva Cilia Hairlike projections that extend from the plasma membrane --- in embryonic development, the presence of cialis is a sign that differentiation has occurred. vegetal hemisphere Bottom portion of the egg which contains the yolk Primary mesenchyme cells Future Mesoderm Cells --- descendants of the micromeres During sea urchin gastrulation, these cells move from vegetal hemisphere to the blastocoel Movement of Primary Mesenchyme Cells - see "Sea Urchin Gastrulation 1", specifically image C-D, for context --- these cells are differentiated by this point --- have cilia Initially, these cells have several cell-adhesion proteins between adjacent cells proteins that bind the cells together --- causes a change in cytoskeleton dynamics so they are cube-shaped These cells are separated from the blastocoel by two layers 1) Basal Lamina, a layer of proteins that covers these cells and acts as an anchor Basal lamina acts as an anchor holding them in place 2) Extracellular matrix fibril, a long string of protein involved in the changing shape of the blastula Dissociation and Movement into Blastocoel Steps: 1) The cells suddenly lose their cell-adhesion proteins 2) Lack of cell adhesion proteins means they are no longer forced to be cube-shaped (cytoskeleton are no longer confined) and so these cells begin to expand/wiggle out from neighboring cells and pass through the basal lamina 4) Cells become more elongated until bit-by-bit they make their way up to the extracellular matrix fibril --- sometimes division can occur in the middle of this process (see pic D-E) archenteron - the primitive gastric cavity of an embryo - ---- eventually becomes the passageway used by the anus to dispel waste Blastopore - In gastrulation, it's the indentation formed at the very tip of the canal ---- becomes the anus in sea urchins secondary mesenchyme cells - are a heterogeneous population of cells with several different fates and behaviours. Taken together, a number of evidence indicates that SMCs function as multipotent stem cells skeletal rods - Part of their body part Stomodeum - primitive mouth in embryo Pluteus - larval stage of sea urchin prism stage just before pluteus (larval stage) SEM of primary mesenchyme cells inside the blastocoel [sea urchin - cross section] SEM of blastopore [sea urchin] SEM showing archenteron [sea urchin - cross section]

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