In Drosophila, loss-of-function Ultrabithorax mutations result in the posterior thoracic segments differentiating into body parts with an identity normally found in the anterior thoracic segments. When the Ultrabithorax gene was cloned, it was shown to encode a transcription factor and to be expressed only in the posterior region of the thorax. Thus, Ultrabithorax acts to specify the identity of the posterior thoracic segments. Similar genes were soon discovered in other animals, including mice and humans. You have found that mice possess two closely related genes, Hoxa7 and Hoxb4, which are orthologs of Ultrabithorax. You wish to know whether the two mouse genes act to specify the identity of body segments in mice.
How will you determine where and when the mouse genes are expressed?

Verified step by step guidance

1. Step 1: Design an experiment to determine the spatial expression of Hoxa7 and Hoxb4 in mice. Use in situ hybridization or immunohistochemistry techniques to visualize the location of mRNA or protein expression in mouse tissues. Prepare tissue sections from various developmental stages and regions of the mouse body.
2. Step 2: Create probes or antibodies specific to Hoxa7 and Hoxb4. For in situ hybridization, synthesize labeled RNA probes complementary to the mRNA sequences of Hoxa7 and Hoxb4. For immunohistochemistry, generate or obtain antibodies that specifically bind to the Hoxa7 and Hoxb4 proteins.
3. Step 3: Apply the probes or antibodies to the prepared tissue sections. For in situ hybridization, hybridize the labeled RNA probes to the tissue sections under conditions that allow specific binding to the target mRNA. For immunohistochemistry, incubate the tissue sections with the antibodies to detect the proteins.
4. Step 4: Visualize the expression patterns using appropriate detection methods. For in situ hybridization, use fluorescence or enzymatic detection to observe the bound probes under a microscope. For immunohistochemistry, use secondary antibodies conjugated to fluorescent dyes or enzymes to visualize the protein localization.
5. Step 5: Analyze the results to determine the spatial and temporal expression patterns of Hoxa7 and Hoxb4. Compare the expression patterns to the development of body segments in mice to infer whether these genes specify segment identity, similar to Ultrabithorax in Drosophila.

Key Concepts

Gene Expression

Gene expression refers to the process by which information from a gene is used to synthesize functional gene products, typically proteins. Understanding when and where a gene is expressed is crucial for determining its role in development and function. Techniques such as in situ hybridization and quantitative PCR can be employed to analyze gene expression patterns in specific tissues or developmental stages.

Transcription Factors

Transcription factors are proteins that bind to specific DNA sequences to regulate the transcription of genes. They play a critical role in determining the identity and fate of cells during development. In the context of the Ultrabithorax gene, its function as a transcription factor suggests that it influences the expression of downstream target genes that specify segment identity in the thorax.

Orthologs

Orthologs are genes in different species that evolved from a common ancestral gene and typically retain the same function. The identification of Hoxa7 and Hoxb4 as orthologs of Ultrabithorax indicates that they may have similar roles in segment identity specification in mice. Studying orthologs can provide insights into evolutionary conservation of gene function across species.