Transplantation Experiments and Mutants in Embryology
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Questions and Answers

The receptor for Hedgehog (Hh) on neighboring cells is called ______.

Patched

MicroRNA (miRNA) is processed by ______ to form double-stranded RNA.

Dicer

Let-7 miRNA plays a crucial role in cell differentiation and is linked to ______ when overexpressed.

cancers

GLD-1 represses translation in posterior cells by binding to ______ mRNA.

<p>glp-1</p> Signup and view all the answers

In situ hybridization is used for ______ localization in fixed embryos or tissues.

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

Transplanting the dorsal lip of the blastopore in Xenopus laevis leads to the formation of a Siamese twin due to the induction of a secondary embryonic ______.

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

Sonic Hedgehog (Shh) is responsible for reverse polarity and the formation of extra ______ in chick embryos.

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

Cis-acting mutations often result in dominant ______ due to their regulatory effects.

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

Homeotic genes in Drosophila control the identity of ______ parts.

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

The method known as In Situ Hybridization is used to detect mRNA ______.

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

Bicoid, expressed at the anterior, helps establish a gradient to activate anterior ______.

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

Even-skipped is a pair-rule gene that affects ______-numbered segments in Drosophila.

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

The gene cluster known as Bithorax controls thoracic and ______ segments in Drosophila.

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

Engrailed and Wingless are crucial in segment patterning, dictating anterior vs. ______ borders.

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

Mutations in regulatory elements can affect the expression of Sonic Hedgehog (Shh) without altering the ______ region.

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

Flashcards

Hedgehog (Hh)

A signaling molecule that acts as a paracrine factor, meaning it influences neighboring cells. It's produced by cells expressing the engrailed gene.

Patched (Ptc)

A receptor on the surface of cells that binds to Hedgehog, activating downstream signaling pathways. When it binds Hh, it triggers the production of another signaling factor called Wingless (Wg).

Feedback Loop

A regulatory mechanism where the product of a signaling pathway influences the expression of its own regulators, helping to maintain stable signaling levels.

MicroRNAs (miRNAs)

Short non-coding RNA molecules that regulate gene expression by binding to messenger RNA (mRNA) and either blocking translation or promoting its degradation.

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GLD-1

A protein that prevents the translation of mRNA by binding to it. It's involved in determining cell fate by blocking the production of GLP-1 protein in posterior cells of C. elegans.

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Spemann's Organizer

A region in the dorsal lip of the blastopore in amphibian embryos, responsible for inducing the formation of the secondary embryonic axis.

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Zone of Polarizing Activity (ZPA)

A region in the posterior limb bud that acts as a signaling center, controlling the development of digits and their polarity.

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Sonic Hedgehog (Shh)

A signaling molecule that plays a crucial role in digit development, specifically in the ZPA. It determines the polarity of the digits and can induce formation of additional digits when misexpressed.

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Polydactyly

A condition characterized by the presence of extra fingers or toes. It can be caused by various genetic factors, including mutations in the Shh gene.

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Homeotic Genes

Genes that control the identity of body parts during development in Drosophila, influencing the formation of specific structures such as wings, legs, and antennae.

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Antennapedia Complex

One of the two main groups of homeotic genes in Drosophila that controls the development of the head and thoracic segments. Mutants in this gene family can lead to the development of legs in place of antennae.

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Bithorax Complex

One of the two main groups of homeotic genes in Drosophila that controls the development of the thoracic and abdominal segments. Mutants in this gene family can lead to the development of wings on the third thoracic segment instead of halteres.

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Hox Genes

Genes that are expressed in a spatially restricted domain, with their position on the chromosome reflecting their corresponding body region.

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In Situ Hybridization

A method used to visualize mRNA localization in cells and tissues, revealing the spatial expression patterns of genes throughout development.

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Gap Genes

A group of genes whose mutations result in defects in large body segments, affecting multiple segments simultaneously. These genes act downstream of maternal genes and regulate the expression of pair-rule genes.

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Study Notes

Transplantation Experiments

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

Polydactyly

  • Misexpression 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 (misrepresentation of wing genes).
    • Antennapedia Mutant: Legs develop where antennae normally are (misrepresentation of leg genes).
  • Hox Genes: Two group of related genes that control the body plan of an embryo along the anterior-posterior axis.
  • Comprises:
    • Antennapedia (controls head and thoracic segments)
  • Methods for Gene Expression Visualization
    • In Situ Hybridization: Detect mRNA localization.
    • Antibody-based: Detect protein expression and cDNA clones.
    • Hox Gene Expression:
      • Spatially restricted domains: Hox genes express early in embryogenesis, controlling segment identity.
      • Mutagenesis screens (Wieschaus, Lewis, Nüsslein-Volhard): Discovered maternal and zygotic genes controlling Hox gene expression.

Drosophila Development: Gene Gradients

  • Maternal Genes:
    • Bicoid: Expressed at the anterior; establishes gradient to activate anterior genes.
    • Nanos: Expressed at the posterior; creates gradient for posterior genes.
  • Gap Genes:
    • Krüppel, knirps, Giant, hunchback: Control large segment areas.
    • Bicoid mutants: Missing anterior; Hunchback gene activated.
  • Pair-rule Genes:
    • Even-skipped: Affects even-numbered segments.
    • Fushi tarazu: Affects odd-numbered segments.
    • Stripe formation: Controlled by maternal and gap genes.
  • Segment Polarity Genes: Dictate anterior vs. posterior borders of segments.
    • Engrailed and Wingless: are key in segment patterning.

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Description

This quiz covers key experiments in embryology such as Spemann's Organizer and the effects of polydactyly through Shh misexpression. Additionally, it discusses homeotic mutants in Drosophila, particularly the mechanisms controlling body part identity. Test your understanding of these concepts in developmental biology.

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