Loss-of-Function Mutagenesis for Forward Genetics

Genes are central players regulating biological processes. A general strategy for studying gene function is to impair gene activity and examine its consequences in the organism. The most common and robust approach is abolishing gene function with loss-of-function mutationmutationloss-of-functions. Hermann MullerHermann Muller’s X-ray mutagenesis was the first to demonstrate the isolation of mutations. A drawback of X-ray is that it disrupts more than one gene in most cases by inducing chromosomal breaks. This chapter will discuss forward genetic approaches to generate single gene mutants with chemical mutagens in model organisms. Firstly, the seminal work of Nuesslein-VolhardNuesslein-Volhard and WieschausWieschaus will be introduced to describe the first large-scale mutagenesis for embryonic lethal mutations in Drosophila. This work identified critical genes in embryo body patterning, influencing studies in vertebrate homologs. Secondly, a large-scale genetic screen for loss-of-function mutations in zebrafish will be introduced as a systematic search for essential genes in vertebrates. Thirdly, a forward geneticforward genetic approach for chemical mutagenesis targeting a selected mouse chromosome will be discussed. This screen was the first in the mouse to use a balancer chromosome made with an engineered inversion, resulting in the isolation of many lethal mutations. These examples of large-scale mutagenesis discussed in this chapter demonstrate that genome-wide screens for essential gene mutations initiated in Drosophila can be applied in vertebrates, including mammals.