The AR gene provides instructions for making androgen receptor (AR), a nuclear receptor activated by androgen-receptor binding complex in the cytoplasm and then nuclear translocation, which mainly serves as a DNA-binding transcription factor for the regulation of gene expression, that the androgen-regulated genes are critical for male sexual phenotype development and maintenance (Bennett et al., 2010). As sex hormone, androgen production sustains throughout the whole life. However, during prenatal development and puberty, the critical periods for the sexual differentiation of the brain, there are significant increases in its production. In this way, AR allows appropriate responses of body to androgens.
For Mus musculus, known as house mouse, Huber et al. (2017) suggested that prenatal AR activity has organizational morphological effects in it as brain constitution and individual’s behaviour are hugely influenced by androgens. By the Organizational-activational Hypothesis as stated in Huber et al., the effects of sex hormones would lead to irreversible body and brain structural and functional changes persisting throughout life. For example, handedness and the second-to-fourth digit (2D:4D) ratio are found to be affected by androgen exposure during pre-natal period. Handedness marks cerebral lateralization and expresses brain asymmetry, and experimental evidence shows that it is also on mice exhibiting a paw preference. The ratio, acknowledged for prenatal exposure to androgen, is the length ratio of the second digit to the fourth digit, which is reversely proportional to the exposure to androgen. In Wistar rats, it was influenced by increased levels in testosterone (a type of androgen), that it was masculinized and being sexually dimorphic: smaller in male than in female.
Other parameters, like head size, body length and tail length, were also measured in Huber et al., which demonstrate that body morphology is affected by prenatal androgen exposure. Utilising muscle-specific androgen receptor knockout (ARKO) mice, Davey et al. (2017) found that AR is essential for hind-limb muscle mass accrual in males with myocytic expression, reinforcing that androgens exerts anabolism on mice skeletal muscle mass. These findings demonstrate that the AR gene is significant in the development of body morphology and also the positive regulation of fast-twitch hind-limb muscle mass and physical activity in male mice.
Concerning the genome, Mus musculus strain C57BL/6J has garnered scientists a more comprehensive understanding on rodent-specific biology, as its C57BL/6J genome assembly has fewer gaps and larger size of novel sequence compared with the earlier MGSCv3 draft genome assembly, which, in turn, enables the defining work of 20,120 protein-coding genes and identification of 439 long, non-protein coding RNAs with evidence for transcribed orthologs in human (Church et al., 2009; 2011). Further to the comparison, complex and repetitive landscape of the sequence that was missing or misassembled in the previously published assembly were analysed with the aid of C57BL/6J genome assembly in Church et al. (2009). Thus, the finished C57BL/6J genome assembly of Mus musculus provides the understanding of the derived ancestral biological functions that rodents share with human.