The lateralization and expresses brain asymmetry, and experimental evidence

The AR gene instructs the coding of 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 affected 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 ratio are
found to be affected by exposure to androgen 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 androgen exposure biomarker, refers to the length ratio of the
second digit to the fourth digit of hand, which is reversely proportional to the
androgen exposure. In Wistar rats, it was affected by increased levels in testosterone
(a type of androgen), that it was masculinized and being sexually dimorphic: smaller
in male than in female.

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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. 


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