Transplantation Experiments in Embryology
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Questions and Answers

What is the primary role of Engrailed in the Hedgehog signaling pathway?

  • Expresses Hedgehog, facilitating paracrine signaling (correct)
  • Serves as a receptor for Wingless on neighboring cells
  • Stimulates the production of Wingless signaling
  • Acts as a feedback inhibitor of Hedgehog signaling

What is one of the consequences of the overexpression of Let-7 miRNA in mammals?

  • Repression of oncogenes linked to tumor formation
  • Increased cell differentiation and normal development
  • Association with various types of cancers (correct)
  • Activation of tumor suppressor mechanisms

How does GLD-1 influence the translation of GLP-1 mRNA in C. elegans?

  • GLD-1 enhances the expression of GLP-1 protein in all cells
  • GLD-1 stabilizes GLP-1 mRNA in anterior cells
  • GLD-1 actively promotes translation in posterior cells
  • GLD-1 represses translation by binding to GLP-1 mRNA (correct)

What is the initial step in the In Situ Hybridization technique for mRNA localization?

<p>Synthesize a single-stranded complementary RNA probe (D)</p> Signup and view all the answers

Which of the following best describes the mechanism of action of Let-7 miRNA?

<p>It targets and represses specific genes to control developmental transitions (B)</p> Signup and view all the answers

What is the consequence of transplanting the dorsal lip of the blastopore in Xenopus laevis embryos?

<p>Development of two separate dorsal lips (D)</p> Signup and view all the answers

Which gene is primarily responsible for the reversed polarity and formation of extra digits in limb buds?

<p>Sonic Hedgehog (Shh) (A)</p> Signup and view all the answers

How do cis-acting mutations typically affect phenotypes?

<p>They can produce normal functions despite the mutation (D)</p> Signup and view all the answers

Which of the following correctly describes the role of homeotic genes in Drosophila?

<p>They specify the developmental fate of body parts (B)</p> Signup and view all the answers

What is the result of the misexpression of the Shh gene in atypical limb regions?

<p>Induction of polydactyly (A)</p> Signup and view all the answers

What technique is used for detecting mRNA localization within cells?

<p>In Situ Hybridization (B)</p> Signup and view all the answers

Which of the following accurately depicts the expression pattern of maternal genes in Drosophila development?

<p>They create gradients that activate gap genes (B)</p> Signup and view all the answers

Which of the following is NOT a role of segment polarity genes in Drosophila?

<p>Influence overall body length (A)</p> Signup and view all the answers

In the context of Hox gene expression during embryogenesis, which statement is true?

<p>The order of Hox genes corresponds to body plan positioning (B)</p> Signup and view all the answers

Which pair of homeotic mutants demonstrates incorrect body part identity due to misexpression of adjacent genes?

<p>Bithorax and Antennapedia mutations (D)</p> Signup and view all the answers

Flashcards

Hedgehog (Hh)

A paracrine signaling factor produced by "engrailed" cells. It binds to the Patched receptor on neighboring cells, activating a signaling pathway.

Patched

A cell surface receptor that binds Hedgehog (Hh) and triggers a signaling cascade, ultimately leading to the production of Wingless (Wg).

MicroRNA (miRNA)

A short non-coding RNA molecule that can bind to messenger RNA (mRNA) and regulate its stability and translation. They can be derived from genes or introns.

Translational Control

A process in which mRNA molecules are bound by specific proteins, preventing their translation into proteins. This plays a critical role in cell fate determination.

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In Situ Hybridization

A technique used to detect the location of specific mRNA molecules within cells or tissues. It involves the use of labeled probes that bind to complementary mRNA sequences.

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Sonic Hedgehog (Shh)

A signaling molecule that helps determine the patterning of digits in developing limbs. If its expression is altered, it can result in extra digits or a mirror-image arrangement.

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Homeosis

A process where the identity of a body part is determined by the specific expression of genes. For instance, mutations in homeotic genes can affect the development of limbs and antennae.

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Zone of Polarizing Activity (ZPA)

A region in the developing limb bud that contains the signaling molecule Sonic Hedgehog. Transplanting this region can lead to the formation of extra digits and mirror-image polarity.

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Polydactyly

A phenomenon where extra digits are formed, often due to mutations in genes like Sonic Hedgehog that regulate limb development.

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Hox Genes

A group of genes in Drosophila that play a role in determining the identity of body segments. These genes are arranged on the chromosome in the same order as the segments they control.

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Maternal Effect Genes

Maternal genes that are expressed in the egg and establish gradients of gene products across the embryo. These gradients play a crucial role in defining the anterior-posterior axis during development.

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Gap Genes

Genes that control the development of large sections of the embryo. Mutations in these genes can lead to gaps in the development of segments.

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Segment Polarity Genes

A group of genes involved in establishing the boundaries of individual segments in the Drosophila embryo. These genes act in concert with others to ensure proper segment development.

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Pair-rule Genes

A group of genes involved in establishing the pattern of even and odd segments in the Drosophila embryo. Mutations in these genes lead to disruptions in the regular pattern of segments.

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Study Notes

Transplantation Experiments

  • Dorsal Lip of Blastomere (Spemann's Organizer)
    • Experiment: Transplant dorsal lip of blastomere to a ventral region of recipient embryo.
    • Observed two separate dorsal lips and induced a secondary embryonic axis.
    • Resulted in the formation of a Siamese twin in Xenopus laevis embryos.

Limb Bud Development and Zone of Polarizing Activity (ZPA)

  • Setup: Transplant ZPA from posterior to anterior limb bud position in chick embryos.
  • Result: Extra digits form with reverse polarity (mirror image of original digits).
  • Sonic Hedgehog (Shh): Responsible for reverse polarity and formation of extra digits.

Polydactyly

  • Mis-expression of Shh in atypical limb regions induces extra digits.
  • Mutations in cis-acting regulatory elements controlling Shh expression (not coding region).
  • Properties of Cis-acting Mutations
    • Phenotypes are often dominant due to regulatory effects in cis.
    • Specific regulatory elements affected; other gene functions may remain normal.

Homeotic Mutants in Drosophila

  • Homeotic Genes: Control the identity of body parts.
    • Wildtype: One pair of wings on the second thoracic segment, haltere on the third.
    • Bithorax Mutant: Wings develop on the third thoracic segment (mis-expression of wing genes).
    • Antennapedia Mutant: Legs develop where antennae normally are (mis-expression of leg genes).
  • Hox Genes: Two complex of related genes that control the body plan of an embryo along the anterior-posterior.
    • Antennapedia (controls head and thoracic segments).
  • Gene Order: The order on the chromosome corresponds to the body region from head to tail.
  • Methods for Gene Expression Visualization
    • In Situ Hybridization: Detect mRNA localization.
    • Antibody-based protein expression and cDNA clones.
  • Hox Gene Expression
    • Spatially restricted domains: Hox genes express early in embryogenesis, controlling segment.
    • Mutgenesis screens (Wieschaus, Lewis, Nüsslein-Volhard): Discovered materal and zygotic genes controlling Hox gene expression.

Drosophila Development: Gene Gradients

  1. Maternal Genes

    • Bicoid: Expressed at the anterior; establishes gradient to activate anterior genes.
    • Nanos: Expressed at the posterior; creates gradient for posterior genes.

  2. Gap Genes

    • Krüppel, Krüpps, Giant, Hunchback: Control large segment areas. Bicoid mutants; missing anterior; Hunchback gene activated.

  3. Pair-rule Genes

    • Even-skipped: Affects even-numbered segments.
    • Fushi tarazu: Affects odd-numbered segments.
    • Stripe formation: Controlled by maternal and gap gene combinations.

  4. Segment Polarity Genes

    • Dictate anterior vs. posterior borders of segments.
    • Engrailed and Wingless are key in segment patterning.

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Description

Explore key transplantation experiments in embryology, including Spemann's Organizer and limb bud development. Analyze how these experiments led to groundbreaking findings in the field, such as polydactyly and the role of Sonic Hedgehog. Understand the mechanisms behind these phenomena and their implications in developmental biology.

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