Diversity of Chromosomal Characteristics Among Mammals: With Special Reference to Laboratory Mouse in Cancer Research

Abstract

The class Mammalia is divided into three subclasses: (1) Prototheria including monotremes, (2) Metatheria including marsupials, and (3) Eutheria that include all other mammalian species. Eutherian mammals, which include humans, have chromosome numbers ranging from 2n = 6 (lowest) to 2n = 102 (highest). The karyotype which consists of the chromosome number and morphology is considered to be the characteristic of a given species. Some mammalian species have either only acrocentric chromosomes, as in the case of laboratory mouse, or only metacentric and/or submetacentric chromosomes, as in the case of most hamster species. Some species, on the other hand, have a combination of acrocentric, submetacentric, and metacentric chromosomes, as in the case of humans. In a few rare mammalian species, the X and the Y chromosomes may be fused to an autosome. With the discovery and application of various chromosome identification (banding) techniques, it became apparent that diverse groups of mammalian species share large chromosomal segments or even many intact chromosomes. Here, I have discussed in brief chromosomal characteristics of various mammalian species with special reference to the laboratory mouse, Mus musculus, and human, Homo sapiens sapiens and concluded that laboratory mouse may not be a suitable animal model representing all mammalian species including humans. In addition, the discussions presented here suggest that mouse is not the best or ideal laboratory animal model for cancer research and anticancer drug development. In the era of personalized medicine, the time has come to use human mini-organs (organoids) produced in culture vessels following the various somatic cell cloning techniques including the somatic cell nuclear transfer (SCNT), induced pluripotent stem (iPS) cells, and other small molecules induced newly discovered reprogramming methods. Such reprogrammed iPS or SCNT stem cells can be monitored in culture to produce patient-specific different human organoids and used instead of using mouse by the pharmaceutical companies and research institutes for testing drug toxicity and production of more effective new anticancer drugs.