Analysis of breeding and pathology helps refine management practices of a large-scale N'-ethyl-N'-nitrosourea mouse mutagenesis programme

Genetic Modifier Screens in Mice

ENU mutagenesis is a forward genetics strategy in which random mutagenesis and phenotypic screening is used to identify genes based on the phenotype induced when they are mutated. A modifier screen is a type of screen in which mice with a pre-existing phenotype are utilized to identify mutations that can enhance or suppress this phenotype. This approach has the potential to uncover missing pathway members, reveal novel genetic interactions, and pinpoint new drug targets. Considerations when planning a suppressor screen include current knowledge, genomic footprint, penetrance, variance, robustness, latency of the starting phenotype, viability, fertility, genetic background and ENU tolerance of starting strain, screening assay, mouse numbers required, and mutation identification strategy. Practical advice on each of these is provided in this review. Curr. Protoc. Mouse Biol. 2:75-87 © 2012 by John Wiley & Sons, Inc.

A hearing and vestibular phenotyping pipeline to identify mouse mutants with hearing impairment

We describe a protocol for the production of mice carrying N-ethyl-N-nitrosourea (ENU) mutations and their screening for auditory and vestibular phenotypes. In comparison with the procedures describing individual phenotyping tests, this protocol integrates a set of tests for the comprehensive determination of the causes of hearing loss. It comprises a primary screen of relatively simple auditory and vestibular tests. A variety of secondary phenotyping protocols are also described for further investigating the deaf and vestibular mutants identified in the primary screen. The screen can be applied to potentially thousands of mutant mice, produced either by ENU or other mutagenesis approaches. Primary screening protocols take no longer than a few minutes, apart from ABR testing which takes upto 3.5 h per mouse. These protocols have been applied for the identification of mouse models of human deafness and are a key component for investigating the genes and genetic pathways involved in hereditary deafness.

Welfare Phenotyping of Genetically-Modified Mice

Technologies that enable the targeted manipulation of the genome have created new opportunities to study the role and interplay of specific genes in both the regulation and function of physiological and behavioural processes and in the development of pathological conditions. Despite the potential benefits, there are ethical issues in relation to the application of these technologies, some of which relate to the impact on the welfare of the animals involved. Matters of concern include the methods involved in the derivation and production of genetically-modified (GM) animals and resulting phenotypes, where animal welfare is compromised. In the case of the latter, this may be the predicted consequence of the genetic modification, but the occurrence of unforeseen animal welfare complications is a major challenge in the management of GM animals. There has been a rapid escalation in the development of new GM lines, most of them involving mice. Databases of available lines have been developed by national and international consortia, and researchers have developed standard protocols to describe the phenotype of a new line; increasingly, such data are entered into these databases. The inclusion of animal welfare assessments with these data would provide a powerful and sophisticated tool to promote refinement. The scope, level and frequency of monitoring would facilitate the identification of unpredicted effects and the management of humane endpoints, and would identify opportunities to manage the animals so as to ameliorate negative impacts. Furthermore, by highlighting the subtleties of gene–environment interactions, such data have wider implications in achieving the goals of refinement.