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?

Key Concepts

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.