Methods for Using the Mouse Lymphoma Assay to Screen for Chemical Mutagenicity and Photo-Mutagenicity

The mouse lymphoma assay (MLA) quantifies genetic alterations affecting expression of the thymidine kinase (Tk ) gene which is located on chromosome 11. This assay is widely used for evaluating the genotoxic potential of various agents. It can also be used for photo-mutagenicity. The Tk -deficient mutants in the MLA result not only from point mutations but also from gross structural and numerical changes at the chromosomal level. The MLA has been recommended as one component of the genotoxicity test battery in many regulatory authorities, countries, and international organizations. The protocol for the MLA has been optimized and adopted by many laboratories around the world. In this chapter, the authors provide an example of the application of the MLA by detailing the procedures that are used for performing the assay in their laboratory and analyzing and interpreting the data generated from both the soft-agar and microwell versions of the assay. In addition, they provide information for using the assay for the analysis of potential photo-mutagenicity.