Origin of Agouti-Melanistic Polymorphism in Wild Black Rats (Rattus rattus) Inferred from Mc1r Gene Sequences

Abstract

We examined nucleotide changes that underlie coat color variation in Black Rats (the Rattus rattus species complex), which show polymorphism in dorsal fur color, including either grayish brown (agouti) or black (melanistic) forms. We examined the full coding sequence of a gene known to produce melanism in other vertebrates-melanocortin-1-receptor gene Mc1r (954 bp) -using samples of both R. rattus (with 2n = 38) and its close relative Asian Black Rat (R. tanezumi; 2n = 42). We used 61 specimens from Japan with karyotype-known individuals and four samples from Pakistan. We found 11 allele sequences and constructed a network tree that shows two distinct clusters, with allelic segregation according to karyotype and by inference, representing the two species. We found that a nucleotide substitution from G to A at site 280, producing an amino acid change from glutamic acid to lysine, was associated with the dominant trait of the melanistic form of the coat color in R. rattus. Notably, the derived SNP 280A was found in a single allele, with the ancestral SNP 280G present in seven alleles. By contrast, all three alleles for R. tanezumi retain the ancestral SNP 280G. These results suggest a possible recent origin of melanism in R. rattus.

Genetic characterization of Okinawan black rats showing coat color polymorphisms of white spotting and melanism

“…Both genes reportedly affect coat color changes in a variety of mammalian species (e.g., Vage et al, 1997;Eizirik et al, 2003;Hosoda et al, 2005;Kingsley et al, 2009). In a previous study of rats from the Otaru port on Hokkaido, where the dorsal agouti and black polymorphism exist, we found that the Otaru rats have the dominant system of melanism in which a single-nucleotide polymorphism (SNP) of Mc1r, i.e., a change from G to A at site 280 that leads to the replacement of glutamic acid with lysine in the amino acid sequence, causes the melanism (Kambe et al, 2011). To date, the molecular details related to the recessive system of melanism in black rats have not yet been determined.…”

“…Representative individuals were subjected to gene sequence analysis. Mc1r sequences were determined for 11 specimens captured in 2009, 6 of which had been previously analyzed (Kambe et al, 2011).…”

“…R. rattus has been introduced more recently to Japan and has hybridized with the native lineage of R. tanezumi. The introduction of genetic components of R. rattus has been inferred from cytogenetic and molecular analyses (Suzuki et al, 2001;Chinen et al, 2005;Kambe et al, 2011). Such introductions have occurred throughout Japan in a variety of environments, including ports (Otaru and Kagoshima), large towns (Tokyo), and insular regions (the Ogasawara Islands).…”

“…Such introductions have occurred throughout Japan in a variety of environments, including ports (Otaru and Kagoshima), large towns (Tokyo), and insular regions (the Ogasawara Islands). The Mc1r sequences of six individuals from Okinawa have indicated that they are R. tanezumi (Kambe et al, 2011); however, intensive studies assessing the phylogenetic background of Okinawan rats has not yet been conducted. In the present study, we conducted a large-scale survey to determine the frequencies of the coat color variants of white spotting and melanism in Yambaru forests.…”

Variation in the Coat-Color-Controlling Genes,Mc1randAsip, in the House MouseMus musculusfrom Madagascar

“…In the case of black rats (Rattus rattus species complex), efforts to determine the gene responsible for the melanistic form have elucidated evolutionary genetic relationships and possible causative mutations (Kambe et al 2011(Kambe et al , 2012Yasuda et al 2014;Chingangbam et al 2015).…”