1. If gene transcription is inhibited after fertilization, development past the two-cell stage does not take place in the mouse. However, in frog embryos, this treatment does not disrupt development until late cleavage. Explain this difference.

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Chapter50: Animal Development
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F. Written Response
1. If gene transcription is inhibited after fertilization, development past the two-cell stage
does not take place in the mouse. However, in frog embryos, this treatment does not
disrupt development until late cleavage. Explain this difference.
2. Twist transcription factors (TF) play key roles in embryonic development and are largely
undetectable in normal adult tissues; however, their expression is reactivated during tumor
progression and correlates with invasive and metastatic lesions. Transcription of the Twist
gene is activated by Wnt signals and the Twist TF represses the gene for E-cadherin.
Answer the following questions as briefly as possible, based on what was presented in class,
not an internet search (complex answers that go beyond class material may lose points)
a. Outline the steps from the Wnt signal to the E-cadherin gene (inclusive);
e.g., A → B → C (with some clarifications such as "binds to", "activates", "represses")
b. What are the normal cellular and embryonic (morphological) consequences of Twist expression?
c. How would inappropriate expression contribute to cancer?
3. Propose a model that outlines, step-by-step, events that could generate the gradients of
transcription factors shown in the lower panel of the figure below. The upper panel
illustrates gradients formed during the first step - start here. The gradients are marked with
letters or numbers and should be used to identify the gradients in your answer. A & B may or
may not represent the same molecules in the lower panel (e.g., A may or may not become 1).
All 4 "general lessons" of spatial regulation of gene expression by morphogen gradients
must be illustrated in the answer.
Relative protein concentration
Ventral
A
↑
2
/B
Dorsal
Transcribed Image Text:F. Written Response 1. If gene transcription is inhibited after fertilization, development past the two-cell stage does not take place in the mouse. However, in frog embryos, this treatment does not disrupt development until late cleavage. Explain this difference. 2. Twist transcription factors (TF) play key roles in embryonic development and are largely undetectable in normal adult tissues; however, their expression is reactivated during tumor progression and correlates with invasive and metastatic lesions. Transcription of the Twist gene is activated by Wnt signals and the Twist TF represses the gene for E-cadherin. Answer the following questions as briefly as possible, based on what was presented in class, not an internet search (complex answers that go beyond class material may lose points) a. Outline the steps from the Wnt signal to the E-cadherin gene (inclusive); e.g., A → B → C (with some clarifications such as "binds to", "activates", "represses") b. What are the normal cellular and embryonic (morphological) consequences of Twist expression? c. How would inappropriate expression contribute to cancer? 3. Propose a model that outlines, step-by-step, events that could generate the gradients of transcription factors shown in the lower panel of the figure below. The upper panel illustrates gradients formed during the first step - start here. The gradients are marked with letters or numbers and should be used to identify the gradients in your answer. A & B may or may not represent the same molecules in the lower panel (e.g., A may or may not become 1). All 4 "general lessons" of spatial regulation of gene expression by morphogen gradients must be illustrated in the answer. Relative protein concentration Ventral A ↑ 2 /B Dorsal
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