Mutagenesis and phenotype

Phenotypic analysis of the bacterial genome will focus on the development, application and adaptation of high throughput techniques to bacteria of emerging medical, biotechnological and agronomical interest such as Pseudomonads. This will involve the use of available methods for rapid genome sequencing and for functional studies by means of high throughput phenotypic analysis with saturation-tagged mutagenesis in combination with DNA array techniques. Emphasis will be placed on exploiting robotisation opportunities and developing new genetic tools (specialized transposons, gene/genome shuffling instruments, molecular assets for metabolic engineering etc) and concepts for computer assisted (if not fully driven) experimentation. This will be facilitated by the relatively low number of genes under scrutiny in bacteria as compared to higher organisms.

The mouse is the model organism of choice for a genome-wide mammalian mutagenesis programme. The murine and human genomes are roughly the same size, some chromosomal regions are syntenic, and homologous proteins share over 90% sequence identity. Embryonic stem (ES) cell technology allows genetic changes made in cell culture to be introduced into live mice and bred into subsequent generations. Large numbers of new mouse strains are being produced. In phenotype-driven screens, random mutations are generated with mutagens such as ethylnitrosourea (ENU) to derive mice with novel phenotypes from which relevant genes are subsequently identified. The advantages are that no assumptions are made with respect to which genes or mutations are involved, and the approach can lead to mouse models for common forms of human genetic disease involving multiple genes. The identification of the mutant gene is not a trivial undertaking, but successful examples include identification of leptin, deafness genes and a Clock gene. To apply fully the power of genetics, multiple alleles of the same gene such as hypomorphs or hypermorphs are required.

It is important to continue with phenotype-driven mutagenesis screens in the mouse. In particular, to close the 'phenotype gap', the relative deficiency in phenotypes, by generating new mouse mutations. As well as the continued development of novel screens, there will be an increasing emphasis on the development of modifier screens that employ mice already carrying a mutation in a pathway of interest. These sensitised screens will allow us to uncover further genetic loci involved in the pathway. Integration with expression profiling and proteomics will allow us to improve the analysis of novel mutations and to dissect the pathways affected. In nearly all animal facilities, the maintenance of breeding colonies is limited and mouse strains have to be archived in an efficient way. Archiving mouse strains by cryopreservation of spermatozoa offers a reliable way of preserving genetically valuable mouse strains and provides an efficient management strategy for animal facilities.

There is already considerable cooperation and interchange of protocols and results between the prinicipal centres working on the mouse, namely the Mammalian Genetics Unit at Harwell and the GSF at Neuherberg. Both provide a nucleus for phenotype-driven screens within Europe. We need to encourage other groups to become part of the mutagenesis network.