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Ch. 13 - Regulation of Gene Expression in Eukaryotes
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 13 - Regulation of Gene Expression in EukaryotesProblem 18b
Chapter 13, Problem 18b

The UG4 gene is expressed in stem tissue and leaf tissue of the plant Arabidopsis thaliana. To study mechanisms regulating UG4 expression, six small deletions of DNA sequence upstream of the gene-coding sequence are made. The locations of deletions and their effect on UG4 expression are shown here. Why does deletion D raise UG4 expression in leaf tissue but not in stem tissue?

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1
Understand the context: The UG4 gene is expressed in both stem and leaf tissues, and the question asks why deletion D specifically raises UG4 expression in leaf tissue but not in stem tissue. This suggests that the deleted region contains regulatory elements that influence tissue-specific expression.
Recall the concept of regulatory elements: Genes are regulated by sequences such as enhancers, silencers, and promoters. These elements can be tissue-specific, meaning they interact with transcription factors that are present only in certain tissues.
Analyze the effect of deletion D: Deletion D raises UG4 expression in leaf tissue. This implies that the deleted region likely contains a silencer or repressor element that normally suppresses UG4 expression in leaf tissue. Removing this silencer allows for increased expression in leaves.
Consider why stem tissue is unaffected: The deletion does not change UG4 expression in stem tissue, suggesting that the silencer or repressor element in the deleted region is not active in stem tissue. This could be because the transcription factors required to activate the silencer are absent in stem tissue.
Conclude the reasoning: Deletion D removes a leaf-specific silencer or repressor element, leading to increased UG4 expression in leaf tissue. However, since this silencer is not functional in stem tissue, UG4 expression remains unchanged in that tissue.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gene Regulation

Gene regulation refers to the mechanisms that control the expression of genes, determining when and how much of a gene product is made. This can involve various elements such as promoters, enhancers, and silencers, which interact with transcription factors to modulate gene activity. Understanding these regulatory elements is crucial for interpreting how specific deletions can affect gene expression in different tissues.
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Review of Regulation

Tissue-Specific Expression

Tissue-specific expression is the phenomenon where certain genes are expressed in specific tissues or developmental stages of an organism. This is often regulated by the presence of unique transcription factors or regulatory elements that are active only in those tissues. In the case of the UG4 gene, its differential expression in leaf versus stem tissue suggests that distinct regulatory mechanisms are at play in these tissues.
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Deletion Mutations

Deletion mutations involve the removal of a segment of DNA, which can impact gene expression by altering the regulatory regions that control transcription. Depending on the location and size of the deletion, it can either enhance or repress gene expression. In this scenario, understanding how deletion D affects the regulatory landscape upstream of the UG4 gene is key to explaining its increased expression in leaf tissue.
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Related Practice
Textbook Question

A hereditary disease is inherited as an autosomal recessive trait1. The wild-type allele of the disease gene produces a mature mRNA that is 1250 nucleotides (nt) long. Molecular analysis shows that the mature mRNA consists of four exons that measure 400 nt (exon 1), 320 nt (exon 2), 230 nt (exon 3), and 300 nt (exon 4). A mother and father with two healthy children and two children with the disease have northern blot analysis performed in a medical genetics laboratory. The results of the northern blot for each family member are shown here. Identify the genotype of each family member, using the sizes of mRNAs to indicate each allele. (For example, a person who is homozygous wild type is indicated as '1250/1250.')

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Textbook Question

A hereditary disease is inherited as an autosomal recessive trait1. The wild-type allele of the disease gene produces a mature mRNA that is 1250 nucleotides (nt) long. Molecular analysis shows that the mature mRNA consists of four exons that measure 400 nt (exon 1), 320 nt (exon 2), 230 nt (exon 3), and 300 nt (exon 4). A mother and father with two healthy children and two children with the disease have northern blot analysis performed in a medical genetics laboratory. The results of the northern blot for each family member are shown here. Based on your analysis, what is the most likely molecular abnormality causing the disease allele?

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Textbook Question

The UG4 gene is expressed in stem tissue and leaf tissue of the plant Arabidopsis thaliana. To study mechanisms regulating UG4 expression, six small deletions of the DNA sequence upstream of the gene-coding sequence are made. The locations of deletions and their effect on UG4 expression are shown here. Explain the differential effects of deletions B and F on expression in the two tissues.

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Textbook Question

The UG4 gene is expressed in stem tissue and leaf tissue of the plant Arabidopsis thaliana. To study mechanisms regulating UG4 expression, six small deletions of DNA sequence upstream of the gene-coding sequence are made. The locations of deletions and their effect on UG4 expression are shown here. Why does deletion E lower expression of UG4 in leaf tissue but not in stem tissue?

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Textbook Question

Diagram and explain how the inducibility of a gene—for instance in response to an environmental cue—could be mediated by an activator. Then show how it could be mediated by a repressor.

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Textbook Question

A muscle enzyme called ME1 is produced by transcription and translation of the ME1 gene in several muscles during mouse development, including heart muscle, in a highly regulated manner. Production of ME1 appears to be turned on and turned off at different times during development. To test the possible role of enhancers and silencers in ME1 transcription, a biologist creates a recombinant genetic system that fuses the ME1 promoter, along with DNA that is upstream of the promoter, to the bacterial lacZ (β-galactosidase) gene. The lacZ gene is chosen for the ease and simplicity of assaying production of the encoded enzyme. The diagram shows bars that indicate the extent of six deletions the biologist makes to the ME1 promoter and upstream sequences. The blue deletion labeled D is within the promoter whereas the gray bars span potential enhancer/silencer modules. The table displays the percentage of β-galactosidase activity in each deletion mutant in comparison with the recombinant gene system without any deletions.



Does this information indicate the presence of enhancer and/or silencer sequences in the ME1 upstream sequence? If so, where is/are the sequences located? 

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