Chapter 15: transcription regulation in eukaryotes

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Questions and Answers

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

Acts as a receptor for Hedgehog. (correct)

Stimulates the expression of engrailed.

Inhibits Wingless production.

Promotes negative feedback in the signaling pathway.

Which of the following describes the function of Let-7 microRNA in mammals?

Enhances transcriptional activity in stem cells.

Promotes uncontrolled cell division.

Regulates protein expression during cell differentiation. (correct)

Inhibits the function of mRNA-binding proteins.

How does GLD-1 affect GLP-1 mRNA translation in C. elegans?

It facilitates the transcription of GLP-1.

It represses translation by binding to mRNA. (correct)

It completely degrades the mRNA.

It enhances the translation process.

What is the initial step in performing in situ hybridization for mRNA localization?

Synthesize a single-stranded RNA probe complementary to the target mRNA. Signup and view all the answers

Which gene targets are linked to the tumor suppressor function of let-7 microRNA?

Myc, Cyclin D, and CDK6. Signup and view all the answers

What was the result of transplanting the dorsal lip of the blastopore in Xenopus laevis embryos?

Induction of a secondary embryonic axis Signup and view all the answers

Which gene is responsible for inducing reverse polarity and extra digit formation in chick limb buds?

Sonic Hedgehog (Shh) Signup and view all the answers

What is a characteristic of cis-acting mutations affecting gene regulation?

They can have dominant phenotypic effects. Signup and view all the answers

Which type of mutation in Drosophila is characterized by legs developing where antennae normally are?

Antennapedia Mutant Signup and view all the answers

What method is used to visualize mRNA localization in gene expression studies?

In Situ Hybridization Signup and view all the answers

What is the role of maternal gene Bicoid during early* Drosophila* embryogenesis?

To activate anterior gene expression Signup and view all the answers

In the context of Drosophila development, which genes regulate large segment areas?

Gap Genes Signup and view all the answers

Which of the following genes affects odd-numbered segments in Drosophila?

Even-skipped Signup and view all the answers

What defines the order of Hox genes on a chromosome in Drosophila?

The body region they control Signup and view all the answers

Which gene gradient creates a posterior expression pattern in Drosophila development?

Nanos Signup and view all the answers

Study Notes

Transplantation Experiments

Dorsal Lip of Blastomere (Spemann's Organizer)
- Experiment: Transplant dorsal lip of blastomere 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.

Why Xenopus laevis?

Pigmented eggs, allowing clear identification of the dorsal surface (black).

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 complexes of related genes that control the body plan of an embryo along the anterior-posterior axis.
- Antennapedia (controls head and thoracic segments).

Methods for Gene Expression Visualization

In Situ Hybridization: Detect mRNA localization.
Antibody-based protein expression and cDNA clones:
- Spatially restricted domains: Hox genes express early in embryogenesis, controlling segment.
- 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:
- Kruppel, 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 gene combinations.
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 explores key transplantation experiments, including the role of Spemann's Organizer in Xenopus laevis and the implications of the Zone of Polarizing Activity in limb bud development. It examines the mechanisms leading to phenomena like polydactyly and the contributions of Sonic Hedgehog in digit formation. Test your understanding of embryonic induction and limb patterning.