Genotype-dependent participation of coat color gene loci in the behavioral traits of laboratory mice

Coat Color-Facilitated Efficient Generation and Analysis of a Mouse Model of Down Syndrome Triplicated for All Human Chromosome 21 Orthologous Regions

Down syndrome (DS) is one of the most complex genetic disorders in humans and a leading genetic cause of developmental delays and intellectual disabilities. The mouse remains an essential model organism in DS research because human chromosome 21 (Hsa21) is orthologously conserved with three regions in the mouse genome. Recent studies have revealed complex interactions among different triplicated genomic regions and Hsa21 gene orthologs that underlie major DS phenotypes. Because we do not know conclusively which triplicated genes are indispensable in such interactions for a specific phenotype, it is desirable that all evolutionarily conserved Hsa21 gene orthologs are triplicated in a complete model. For this reason, the Dp(10)1Yey/+;Dp(16)1Yey/+;Dp(17)1Yey/+ mouse is the most complete model of DS to reflect gene dosage effects because it is the only mutant triplicated for all Hsa21 orthologous regions. Recently, several groups have expressed concerns that efforts needed to generate the triple compound model would be so overwhelming that it may be impractical to take advantage of its unique strength. To alleviate these concerns, we developed a strategy to drastically improve the efficiency of generating the triple compound model with the aid of a targeted coat color, and the results confirmed that the mutant mice generated via this approach exhibited cognitive deficits.

Regional expression of tyrosinase in central catecholaminergic systems of colored mice

A relationship between coat color and behavioral characteristics has been reported for numerous species. We previously indicated that particular behavioral traits contributing to the genotype at the agouti locus manifest only when possessing a wild-type allele at the albino (i.e., tyrosinase: Tyr) locus. The present study was performed to investigate tyrosinase expression with marked activity in central nervous systems. The whole brain of male B10 and B10-c mice, a B10 congenic strain of the albino locus from BALB/c, at 8 to 9 weeks of age was removed, and obtained several regions of brain, especially catecholaminergic. Comparatively large amounts of Tyr mRNA and its translation products of approximately 68 kDa were found in the regions obtained, and definitely possessed the enzyme activity for the oxidation of L-tyrosine. The present results indicate the possibility that the amount of catecholamines produced in albino mice is higher than that of colored mice due to the deficit in tyrosinase heritably.

Molecular analyses of the agouti allele in the Japanese house mouse identify a novel variant of the agouti gene

It has been thought that the Japanese house mouse carries the A^w allele at the agouti locus causing light-colored bellies, but they do not always show this coloration. Thus, the presence of the A^w allele seems to be doubtful in them. To ascertain whether the A^w allele is present, a two-pronged approach was used. First, we compared lengths of DNA fragments obtained from three PCRs conducted on them to the known fragment sizes generated from mouse strains exhibiting homozygosities of either a/a, A/A, or A^w/A^w. PCR I, PCR II, and PCR III amplify only in the A and A^w alleles, the a and A^w alleles, and the a allele, respectively, and we detected amplifications in strains with A/A and A^w/A^w by PCR I, in those with a/a and the Japanese house mouse by PCR II, and in those with a/a by PCR III. Second, we sequenced the exon 1A region of the agouti gene and obtained sequences corresponding to the above strains and the Japanese house mouse, but their sequences were similar to those of the a allele. We concluded that their agouti allele is not identical to the A^w allele and seems to be a novel type similar to the a allele.

Modulation of social behavior by the agouti pigmentation gene

Agouti is a secreted neuropeptide that acts as an endogenous antagonist of melanocortin receptors. Mice and rats lacking agouti (called non-agouti) have dark fur due to a disinhibition of melanocortin signaling and pigment deposition in the hair follicle. Non-agouti animals have also been reported to exhibit altered behavior, despite no evidence for the expression of agouti outside the skin. Here we confirm that non-agouti mice show altered social behavior and uncover expression of agouti in the preputial gland, a sebaceous organ in the urinary tract that secretes molecules involved in social behavior. Non-agouti mice had enlarged preputial glands and altered levels of putative preputial pheromones and surgical removal of the gland reversed the behavioral phenotype. These findings demonstrate the existence of an autologous, out-of-skin pathway for the modulation of social behavior.

The role of humans in facilitating and sustaining coat colour variation in domestic animals

Though the process of domestication results in a wide variety of novel phenotypic and behavioural traits, coat colour variation is one of the few characteristics that distinguishes all domestic animals from their wild progenitors. A number of recent reviews have discussed and synthesised the hundreds of genes known to underlie specific coat colour patterns in a wide range of domestic animals. This review expands upon those studies by asking how what is known about the causative mutations associated with variable coat colours, can be used to address three specific questions related to the appearance of non wild-type coat colours in domestic animals. Firstly, is it possible that coat colour variation resulted as a by-product of an initial selection for tameness during the early phases of domestication? Secondly, how soon after the process began did domestic animals display coat colour variation? Lastly, what evidence is there that intentional human selection, rather than drift, is primarily responsible for the wide range of modern coat colours? By considering the presence and absence of coat colour genes within the context of the different pathways animals travelled from wild to captive populations, we conclude that coat colour variability was probably not a pleiotropic effect of the selection for tameness, that coat colours most likely appeared very soon after the domestication process began, and that humans have been actively selecting for colour novelty and thus allowing for the proliferation of new mutations in coat colour genes.