Consider the even-skipped regulatory sequences in Figure 18.9.

How are the sharp boundaries of expression of eve stripe 2 formed?

Verified step by step guidance

1. Understand that the sharp boundaries of expression of eve stripe 2 are formed through the interaction of transcriptional activators and repressors binding to specific regulatory sequences in the DNA.
2. Identify the activators involved in the regulation of eve stripe 2. These activators, such as Bicoid and Hunchback, bind to the enhancer region of the eve gene and promote transcription in specific regions of the embryo.
3. Recognize the role of repressors, such as Giant and Kruppel, which bind to the same regulatory region and inhibit transcription in areas where they are expressed, creating sharp boundaries.
4. Analyze the spatial distribution of these activators and repressors in the embryo. The overlapping gradients of these proteins ensure that eve stripe 2 is expressed only in a narrow band where activators are present and repressors are absent.
5. Conclude that the sharp boundaries of eve stripe 2 expression are a result of the precise balance and spatial distribution of activators and repressors, which interact with the regulatory sequences to control gene expression in a highly localized manner.

Key Concepts

Regulatory Sequences

Regulatory sequences are regions of DNA that control the expression of genes. They can include enhancers, silencers, and promoters, which interact with transcription factors to modulate gene activity. In the context of the even-skipped (eve) gene, these sequences are crucial for determining where and when the gene is expressed during development.

Transcription Factors

Transcription factors are proteins that bind to specific DNA sequences to regulate gene expression. They can act as activators or repressors, influencing the transcription of target genes. In the case of eve stripe 2, specific transcription factors bind to the regulatory sequences, creating sharp boundaries of expression by either promoting or inhibiting transcription in adjacent regions.

Positional Information and Morphogens

Positional information refers to the spatial cues that cells use to determine their fate during development. Morphogens are signaling molecules that create concentration gradients, providing this positional information. In the formation of eve stripe 2, morphogen gradients help establish the precise boundaries of gene expression by influencing the activity of transcription factors in a spatially restricted manner.