The Hoxd9–13 genes are thought to specify digit identity. You wish to examine the effect of loss-of-function alleles in developing limbs. How would you construct a mouse in which the function of Hoxd9–13 is retained during anterior–posterior embryonic patterning but is absent from developing limbs?

Verified step by step guidance

1. Step 1: Understand the role of Hoxd9–13 genes. These genes are involved in specifying digit identity during limb development and anterior-posterior embryonic patterning. Loss-of-function alleles can help determine their specific role in limb development.
2. Step 2: Use a conditional knockout approach to selectively remove the function of Hoxd9–13 genes in developing limbs while retaining their function in anterior-posterior embryonic patterning. This requires the use of Cre-Lox recombination technology.
3. Step 3: Design a mouse model with a floxed Hoxd9–13 allele. This involves flanking the Hoxd9–13 gene with LoxP sites, which allows the gene to be excised in the presence of Cre recombinase.
4. Step 4: Select a limb-specific Cre driver. For example, use a promoter that is active only in developing limb tissues, such as the Prx1 promoter, to drive Cre expression specifically in the limbs.
5. Step 5: Cross the floxed Hoxd9–13 mouse with the limb-specific Cre mouse. The offspring will have Hoxd9–13 function retained in anterior-posterior embryonic patterning but will lose its function in developing limbs due to Cre-mediated excision of the floxed allele.

Key Concepts

Hox Genes

Hox genes are a group of related genes that determine the body plan and the identity of body segments in animals. They play a crucial role in embryonic development by regulating the expression of other genes that control the formation of limbs and other structures. In particular, the Hoxd9–13 genes are involved in specifying digit identity, influencing how limbs develop and what types of digits are formed.

Loss-of-Function Alleles

Loss-of-function alleles are mutations that result in the reduced or abolished function of a gene. In the context of Hoxd9–13, creating loss-of-function alleles would help researchers understand the specific roles these genes play in limb development. By analyzing the phenotypic consequences of these mutations, scientists can infer how the absence of Hoxd9–13 affects digit identity and limb morphology.

Conditional Gene Knockout

A conditional gene knockout is a genetic engineering technique that allows for the selective inactivation of a gene in specific tissues or at specific developmental stages. This approach is particularly useful for studying essential genes like Hoxd9–13, as it enables researchers to retain gene function in other areas (like anterior-posterior patterning) while eliminating it in developing limbs. Techniques such as Cre-loxP recombination are commonly used to achieve this targeted gene disruption.