The mouse genetics toolkit: revealing function and mechanism

Abstract

Large-scale projects are providing rapid global access to a wealth of mouse genetic resources to help discover disease genes and to manipulate their function.

Figure 1

Gene targeting strategies used in mouse ES cells. Targeting is achieved by recombination (black crosses) between homology arms (red lines). (a) A knockout vector replaces an entire gene with a selection cassette containing drug resistance (D^R), enabling the selection of successfully targeted ES cell clones. (b) A knock-in vector allows the expression of a transgene, such as LacZ or Cre, by the promoter (gray arrow) of the targeted gene. (c) Insertion vectors can interfere with splicing by disrupting a target gene by the introduction of an exon with an early termination codon or a 5' splice acceptor site (SA). They typically target the genome with a single crossover event. (d) A conditional allele with directional DNA sequences (LoxP, green triangles) either side of a critical exon. Recombination between the sites will result in a null allele. (e) LoxP sites can also be targeted megabases apart, either side of a larger cluster of genes, enabling chromosome engineering. (f) Heterospecific Lox sites, such as LoxP and Lox511, are targeted by the site-specific recombinase Cre. Recombinase-mediated cassette exchange (RMCE) enables the efficient swapping of one targeted cassette containing incompatible target sites for another cassette flanked by an identical pair of sites. This enables the rapid generation of new alleles, such as introducing a point mutation in a critical exon.

Figure 2

Phenotypic screening of genetically modified mice. Mutant mice available to the community are systematically screened for a range of phenotypes by the Sanger Mouse Genetics Project and the data published online [10]. Some examples of observed phenotypes are shown. (a) An outwardly protruding xiphoid process in Fam73b^{tm1a(KOMP)Wtsi} homozygous mice (top), compared with wild-type controls (bottom). (b) The formation of uroliths (bladder stones) in Clnd16^{tm1a(KOMP)Wtsi} homozygous mice (top), not present in controls (bottom). (c) Underdeveloped molars in Sparc^{tm1a(EUCOMM)Wtsi} homozygous mice (top), compared with control mice (bottom). (d) Abnormal skeletal muscle in Zfp106^{tm1a(KOMP)Wtsi} homozygous mice (top), compared with controls (bottom). (e) A shortened, upturned snout in Smc3^{tm1a(EUCOMM)Wtsi} heterozygous mice. (f) Metacarpophalangeal joint fusion in Dnase1l2^{tm1(KOMP)Wtsi} homozygous mice. (g) Spots of retinal hyperpigmentation in Slc9a8^{tm1a(KOMP)Wtsi} homozygous mice. (h) LacZ reporter gene expression in the adult mammary gland of Myh9^{tm1a(EUCOMM)Wtsi} heterozygous mice.