The Drosophila even-skipped (eve) gene is expressed in seven stripes in the segmentation pattern of the embryo. A sequence segment of 8 kb 5' to the transcription start site (shown as in the accompanying figure) is required to drive expression of a reporter gene (lacZ) in the same pattern as the endogenous eve gene. Remarkably, expression of most of the seven stripes appears to be specified independently, with stripe 2 expression directed by regulatory sequences in the region 1.7 kb 5' to the transcription start site. To further examine stripe 2 regulatory sequences, you create a series of constructs, each containing different fragments of the 1.7-kb region of the 5' sequence. In the lower part of the figure, the bars at left represent the sequences of DNA included in your reporter gene constructs, and the + and − signs at right indicate whether the corresponding eve-lacZ reporter gene directs stripe 2 expression in Drosophila embryos transformed through P element mediation. How would you interpret the results—that is, where do the regulatory sequences responsible for stripe 2 expression reside?

검증된 단계별 안내

Identify the purpose of the experiment: to determine which DNA fragments within the 1.7 kb region are responsible for directing stripe 2 expression of the eve gene.

Examine the constructs: each construct contains different fragments of the 1.7 kb region linked to a reporter gene (lacZ).

Analyze the results: look at the + and − signs indicating whether each construct successfully directs stripe 2 expression.

Determine the minimal sequence: identify the smallest fragment that still results in a + sign, indicating successful stripe 2 expression.

Conclude the location of regulatory sequences: the minimal fragment that directs stripe 2 expression contains the necessary regulatory sequences.

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영상 길이:

주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Gene Regulation

Gene regulation refers to the mechanisms that control the expression of genes, determining when and how much of a gene product is produced. In the context of the Drosophila even-skipped (eve) gene, regulatory sequences located upstream of the transcription start site play a crucial role in directing the spatial and temporal expression patterns of the gene, such as the formation of stripes in the embryo.

Transcriptional Enhancers

Transcriptional enhancers are specific DNA sequences that enhance the transcription of associated genes. They can be located far from the gene they regulate and function by binding transcription factors, which then interact with the transcription machinery. In this case, the regulatory sequences within the 1.7 kb region upstream of the eve gene are likely enhancers that specifically drive the expression of stripe 2.

Reporter Gene Assays

Reporter gene assays are experimental techniques used to study gene expression and regulatory sequences by linking a reporter gene, such as lacZ, to the regulatory elements of interest. The expression of the reporter gene provides a measurable output, allowing researchers to determine the activity of specific regulatory sequences. In this scenario, the presence or absence of stripe 2 expression in the transformed Drosophila embryos indicates the functionality of the regulatory sequences tested.

관련 실천

교과서 질문

The majority of this chapter focused on gene regulation at the transcriptional level, but the quantity of functional protein product in a cell can be regulated in many other ways as well. Discuss possible reasons why transcriptional regulation or posttranscriptional regulation may have evolved for different types of genes.

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교과서 질문

Microbiologists describe the processes of transcription and translation as 'coupled' in bacteria. This term indicates that a bacterial mRNA can be undergoing transcription at the same moment it is also undergoing translation. Is coupling of transcription and translation possible in single-celled eukaryotes such as yeast? Why or why not?

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교과서 질문

Using the components in the accompanying diagram, design regulatory modules (i.e., enhancer/silencer modules) required for 'your' gene to be expressed only in differentiating (early) and differentiated (late) liver cells. Answer the three questions presented below by describing the roles that activators, enhancers, repressors, silencers, pioneer factors, insulators, chromatin remodeling complexes, and chromatin readers, writers, and erasers will play in the regulation of expression of your gene, that is, what factors will bind and be active in each case? Specify which transcription factors need to be pioneer factors. How will expression be prevented in other cell types?

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