MICE ARE, as it were, the guinea pigs of science. And these days they are often genetically engineered guinea pigs, to boot. The emergence of covid-19, for example, has created demand for laboratory animals that have human versions of a protein called the ACE2 receptor. This molecule is the hook that SARS-COV-2, the virus which causes covid-19, uses to attach itself to a cell before entering and turning that cell into a virus factory. The murine version of ACE2 is, however, the wrong shape for the virus to link up with. That means unmodified mice cannot catch the infection. Hence the need for genetic engineering. The first version of such a mouse has recently become available courtesy of the Jackson Laboratory, a not-for-profit bio-medical research institution in Maine that specialises in breeding laboratory mice. By luck, the team that produced it had a head start. The original sars virus (now known as SARS-COV-1), which came close to causing a pandemic in 2003, also uses ACE2 as its point of entry. As a consequence Stanley Perlman and Paul McCray of the University of Iowa, who were researching SARS, created a mouse with human ACE2 receptors in 2007.
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