On target in the rat

The rat is a widely used animal model for studying human physiology and disease, but functional genomics and genetic research have been stifled by the limited availability of genetargeting tools. QiLong Ying and colleagues have now established gene targeting by homologous recombination in rat embryonic stem cells, and have generated for the first time p53 geneknockout rats, suitable for physiological and pharmacological studies of the ubiquitous tumour suppressor p53. [Letter p. 211; News & Views p. 161]