Mouse

Abstract

The laboratory mouse is an artificial creation, and there is no true "wildtype" laboratory mouse. Furthermore, there is no such thing as "normal" microflora, since laboratory mice are maintained in microbially pristine environments devoid of pathogens and opportunistic pathogens, as well as other commensal flora/fauna. House mice, from which laboratory mice originated, are represented by several species and subspecies native to the Old World. Laboratory mice are largely derived from domesticated "fancy mice" that arose from many years of trading of mouse variants among fanciers in Europe, Asia, North America, and Australia. The laboratory mouse genome, including its retroelements, is a mosaic derived from different subspecies of the Mus musculus complex, including M.m. domesticus, M.m. musculus, M.m. castaneus, M.m. molossinus (a natural hybrid of M.m. musculus and M.m. castaneus), and M. bactrianus.The genome of M.m. domesticus is the predominant contributor to most strains of mice, but many inbred strains share a common "Eve" with a mitochondrial genome of M.m. musculus origin, and a common "Adam" that contributed their Y chromosome from Asian mice. In addition, there is evidence that other Mus species, outside of the M. musculus complex, may have contributed to the genome of some laboratory mouse strains. The C57BL mouse genome contains a contribution from M. spretus. The 1st inbred mouse (DBA), and other strains with DBA genetic contributions, was partially derived from Japanese waltzing mice with M. bactrianus parentage. Perhaps the only laboratory mouse that is derived from a single species (subspecies), M.m. domesticus, is the "Swiss" mouse, but there is a high likelihood that several Swiss stocks and strains have been genetically corrupted.There are over 450 inbred strains of laboratory mice that have arisen during the last century, and these strains, which were selectively inbred to pan-genomic homozygosity for purposes entirely unrelated to modern research, are the foundation upon which literally thousands of spontaneous mutants and GEMs have been built. Additional inbred strains have been developed from wild mice (M.m. castaneus, M. spretus, etc.). Furthermore, "outbred" mice (mostly Swiss mice) are highly homozygous and nearly inbred. There is no such thing as an outbred laboratory mouse with a fully heterozygous genome representative of wildtype M. musculus, and there is no wild mouse genetic counterpart of the laboratory mouse. When working with mice, the pathologist must also become facile with hybrids,