Hydra Model Organism: Regeneration Abilities and Anatomy
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Questions and Answers

What is the primary function of gland cells in Hydra?

  • To facilitate digestion (correct)
  • To regulate water flow
  • To provide structural support
  • To aid in locomotion

    • How do Hydra typically reproduce?

  • Through sexual reproduction
  • Through budding when well fed (correct)
  • By laying eggs
  • By fragmentation

    • What is the significance of Hydra in environmental monitoring?

  • They are a natural predator of aquatic pests
  • They are a keystone species in freshwater ecosystems
  • They are an indicator species for pollution (correct)
  • They are a food source for aquatic animals

    • What is the purpose of BrdU staining in Hydra research?

    <p>To label newly synthesized DNA</p> Signup and view all the answers

    Which of the following cell types is NOT found in the hypostome of Hydra?

    <p>Interstital stem cells</p> Signup and view all the answers

    What is the characteristic body shape of Hydra?

    <p>Radial symmetry</p> Signup and view all the answers

    What is the function of interstital stem cells in Hydra?

    <p>For stinging</p> Signup and view all the answers

    Where are the endodermal epithelial cells located in Hydra?

    <p>On the interior of the animal</p> Signup and view all the answers

    Which part of the Hydra body does not undergo mitosis?

    <p>Tentacles</p> Signup and view all the answers

    What is the typical length of a Hydra individual?

    <p>A few millimeters</p> Signup and view all the answers

    What role does apoptosis play in head regeneration according to the text?

    <p>Apoptosis triggers the initial release of Wnt3 in head regeneration.</p> Signup and view all the answers

    Which signaling molecule is crucial for the development of the proliferative zone during head regeneration?

    <p>Wnt</p> Signup and view all the answers

    What would be the outcome if Sp5 is blocked during head regeneration?

    <p>Multiple ectopic heads</p> Signup and view all the answers

    What happens when beta-catenin is inhibited during foot regeneration?

    <p>More normal phenotype</p> Signup and view all the answers

    Why is Bra1 protein expression significant during head regeneration but not during foot regeneration?

    <p>Bra1 translation is specifically inhibited during foot regeneration.</p> Signup and view all the answers

    What role does Sp5 play in the context of Wnt signaling?

    <p>Represses Wnt3 expression</p> Signup and view all the answers

    What happens to the animal when Bra1 translation is not appropriately regulated during foot regeneration?

    <p>Formation of ectopic patches of basal discs</p> Signup and view all the answers

    What effect does Wnt signaling have when Wnt3 is inhibited?

    <p>Loss of proliferative staining in the head</p> Signup and view all the answers

    Why is beta-catenin important for both head and foot regeneration?

    <p>It regulates foot regeneration independently of Bra1.</p> Signup and view all the answers

    What is the key role of the Head inhibitor in the process of regeneration?

    <p>Preventing head formation</p> Signup and view all the answers

    What percentage of cells are lost at extremities and shed in Hydra?

    <p>15%</p> Signup and view all the answers

    What is the timeframe for the tentacle zone to begin to regrow after cutting the body column in half horizontally?

    <p>48-72 hours</p> Signup and view all the answers

    What is the result of grafting a hypotosome onto the host trunk budding region?

    <p>Induces a secondary axis with another head</p> Signup and view all the answers

    What is the role of the hypostome in Hydra?

    <p>It acts as an organizer, having inductive properties</p> Signup and view all the answers

    What is the molecular signal provided by the transplanted tissue in Hydra bud formation?

    <p>Wnt</p> Signup and view all the answers

    Which of the following cell types is NOT required for regeneration in Hydra?

    <p>Interstitial stem cells (ISCs)</p> Signup and view all the answers

    What is the result of removing Interstitial stem cells (ISCs) from Hydra?

    <p>No effect on regeneration</p> Signup and view all the answers

    What is the role of Wnt in Hydra?

    <p>It is the head organizer</p> Signup and view all the answers

    What is the result of activating Wnt in the budding region of Hydra?

    <p>Formation of ectopic hypostomes everywhere</p> Signup and view all the answers

    What is the purpose of the head inhibition gradient in Hydra?

    <p>To inhibit the formation of multiple heads</p> Signup and view all the answers

    What is the primary function of Interstital stem cells in Hydra?

    <p>For regeneration</p> Signup and view all the answers

    What is the significance of Hydra in environmental monitoring?

    <p>As an indicator of pollution</p> Signup and view all the answers

    Which part of the Hydra body undergoes continuous mitosis?

    <p>The trunk</p> Signup and view all the answers

    What is the purpose of BrdU staining in Hydra research?

    <p>To detect new DNA synthesis</p> Signup and view all the answers

    What is the body shape of Hydra?

    <p>Radial symmetric</p> Signup and view all the answers

    What is the fate of Hydra individuals in polluted freshwater ecosystems?

    <p>They decline in population</p> Signup and view all the answers

    What is the location of endodermal epithelial cells in Hydra?

    <p>Interior of the body</p> Signup and view all the answers

    What is the mode of reproduction in well-fed Hydra?

    <p>Asexual reproduction by budding</p> Signup and view all the answers

    What is the function of gland cells in Hydra?

    <p>For digestion</p> Signup and view all the answers

    What is the major food source of Hydra?

    <p>Small aquatic invertebrates</p> Signup and view all the answers

    What is the outcome when apoptosis is inhibited during head regeneration?

    <p>Reduced foot regeneration</p> Signup and view all the answers

    What is the role of Sp5 in head regeneration?

    <p>Inhibits Wnt signaling</p> Signup and view all the answers

    What is the significance of beta-catenin in foot regeneration?

    <p>Necessary for foot regeneration</p> Signup and view all the answers

    What is the outcome of blocking Sp5 during head regeneration?

    <p>Formation of multiple ectopic heads</p> Signup and view all the answers

    What is the role of Wnt signaling in head regeneration?

    <p>Necessary for head regeneration</p> Signup and view all the answers

    What is the significance of apoptosis in head regeneration?

    <p>Triggers the initial release of Wnt3</p> Signup and view all the answers

    What is the role of the hypostome in Hydra?

    <p>Acts as a head organizer</p> Signup and view all the answers

    What is the significance of Bra1 protein expression during head regeneration?

    <p>Occurs only during head regeneration</p> Signup and view all the answers

    What is the outcome of activating Wnt signaling in the context of head regeneration?

    <p>Regeneration of a head</p> Signup and view all the answers

    What is the role of beta-catenin in regulating foot regeneration?

    <p>Independent of Bra1</p> Signup and view all the answers

    What is the main function of the interstitial stem cells in Hydra regeneration?

    <p>Create specialized cells for nerve regeneration</p> Signup and view all the answers

    Which part of the Hydra body is NOT capable of regeneration according to the text?

    <p>Tentacles</p> Signup and view all the answers

    What is the outcome when both hypostome and basal disc tissues are transplanted together in Hydra regeneration experiments?

    <p>Weak growth or no growth</p> Signup and view all the answers

    What is the role of the head activation gradient in Hydra regeneration?

    <p>Promotes tentacle growth</p> Signup and view all the answers

    Why do experiments involving grafting trunk tissue below the head region show reduced capacity for secondary axis formation?

    <p>Mismatch in polarity gradients</p> Signup and view all the answers

    Which molecular signal maintains apical polarity in Hydra regeneration?

    <p>Wnt</p> Signup and view all the answers

    What is the impact of activating Wnt by adding alsterpaullone in the budding region of Hydra?

    <p>Induces head regeneration</p> Signup and view all the answers

    Which set of cells are shown to create extra heads when mixed in mh-1 mutant chimeras?

    <p>Endodermal cells and epithelial cells</p> Signup and view all the answers

    Which cells are required for head regeneration but not for foot regeneration in Hydra?

    <p>Ectoderm</p> Signup and view all the answers

    What is the main function of the basal disc in Hydra regeneration experiments?

    <p>Induce tail formation</p> Signup and view all the answers

    Study Notes

    Hydra Model Organism

    • Hydra is a freshwater cnidarian that lives in unpolluted freshwater ponds, lakes, and streams.
    • They have a radial symmetric body, a few millimeters in length, and eat small aquatic invertebrates.
    • They proliferate asexually by budding when well-fed.
    • Environmentalists use the presence of Hydra as a test of pollution.

    Hydra Anatomy

    • Gland cells are responsible for digestion.
    • Interstitial stem cells are responsible for stinging.
    • Hypostome is the location of the mouth.
    • Endodermal epithelial cells are located on the interior, ectodermal epithelial cells on the exterior, and mesoglea in between.

    Cell Division and Apoptosis

    • Cells are continuously undergoing mitosis.
    • BrdU staining shows that new DNA is being made, but only in the animal's trunk, not in the tentacles or extremities.
    • Apoptosis is necessary and sufficient for head regeneration.
    • Apoptotic cells are seen in the regenerating head region.
    • Inhibition of apoptosis leads to an increase in foot regeneration and a reduction in head regeneration.

    Wnt Signaling

    • Wnt3 expression and nuclear beta-catenin are apoptosis-dependent.
    • Wnt signaling is necessary for the development of the proliferative zone.
    • There is no proliferative staining in the head when Wnt or beta-catenin is knocked out.
    • The pathway: Apoptosis -> Wnt/beta-catenin -> cell proliferation/head regeneration.

    Head Inhibitor

    • The inhibitor Sp5 is upregulated during head regeneration, prevents head formation, inhibits Wnt/beta-catenin signaling, and is activated by Wnt/beta-catenin.
    • Blocking Sp5 results in an animal with multiple ectopic heads.
    • Sp5 requires beta-catenin, and inhibiting beta-catenin results in a more normal phenotype.

    Foot Regeneration

    • Beta-catenin is involved in both head and foot regeneration.
    • Inhibition of beta-catenin inhibits foot regeneration.
    • Overexpression of beta-catenin results in too many head tentacles and ectopic patches of basal discs.
    • Beta-catenin is expressed at the beginning of foot and head regeneration.

    Hydra as a Simple Model for Regeneration

    • Hydra has a single apical-basal axis.
    • Hydra cells are continuously dividing, and there are three types of stem cells.
    • Transplantation experiments identify activating/inhibitory gradients for both head and foot regeneration.
    • Hypostome acts as a head organizer, and Wnt signaling appears to be the head activation signal.
    • Sp5 functions as part of the head inhibitory signal.
    • Apoptosis triggers the initial release of Wnt3 in head, but not foot regeneration.
    • The Ectoderm has the capacity to initiate head regeneration.
    • Beta-catenin regulates foot regeneration independent of Bra1.

    Regeneration Capabilities of Hydra

    • Hydra is capable of regenerating head, foot, and tentacles.
    • Hydra is very plastic as an organism, and can reaggregate and form a new Hydra from a chunk of cells.
    • Within 48-72 hours, if you cut the body column in half horizontally, the tentacle zone will begin to regrow.
    • Graft experiments provided evidence of polarity gradients.

    Polarity Gradients

    • Hypostome grafted onto the host trunk budding region induces a secondary axis with another hypostome (head).
    • Grafts of trunk tissue below the head have a reduced capacity to form a secondary axis.
    • Basal disc grafted into the host trunk budding region induces a secondary axis with another tail.
    • Opposing apical and basal gradients may determine where a new bud is formed.
    • A combination of activating and inhibiting head and foot gradients ensures that there is only one head and one foot.

    Hypostome as an Organizer

    • Hypostome acts as an organizer, having inductive properties, and the body cavity has self-organizing properties.
    • Transplanted tissue provides a molecular signal for growth, not the tissue for growth itself.
    • Wnt is the apical organizer that maintains apical polarity.

    Cell Types Required for Regeneration

    • Endoderm, Ectoderm, and Interstitial stem cells (ISCs) are required for regeneration.
    • Interstitial cell lineage is not required for regeneration.
    • Ectoderm cells are required for head regeneration.
    • Endodermal cells contribute to foot regeneration.

    How is Regeneration Triggered?

    • Regeneration is triggered by apoptosis, which leads to Wnt signaling and the development of the proliferative zone.

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    Description

    Learn about the fascinating abilities of hydra, a freshwater cnidarian organism known for its remarkable regeneration capabilities. Explore its radial symmetric body, feeding habits, asexual reproduction through budding, and its significance as an indicator of environmental pollution.

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