Subgenus Mus Research Articles

Morphological and Molecular Recharacterization of the Rodent Genus Mus from Nepal Based on Museum Specimens

The taxonomy and phylogeny of the subgenus Mus, the Eurasian lineage of the genus Mus, remain unresolved, even for the house mouse (Mus musculus). While the subgenus is diverse in Asia, few studies cover both its morphology and molecular phylogeny. We re-examined 70 specimens identified as M. cervicolor that were collected from central Nepal in 1968 and 1975 and are currently deposited in the Hokkaido University Natural History Museum. To compare morphological features, we examined skull geometric morphometrics and body coloration, and performed a phylogenetic analysis of the mitochondrial cytochrome b gene sequences of representative specimens. The specimens were most likely either M. booduga or M. musculus. The best morphological characteristics for distinguishing the two species were the nasal length ratio, which was high and low, respectively. Mus booduga was found to inhabit altitudes lower than 1000 m and have light ventral fur, while M. musculus inhabited various altitudes up to 3000 m and had variable fur color depending on the altitude. We also discuss the taxonomic status of the fawn-colored mouse M. cervicolor.

ZP4 Is Present in Murine Zona Pellucida and Is Not Responsible for the Specific Gamete Interaction.

Mammalian eggs are surrounded by an extracellular matrix called the zona pellucida (ZP). This envelope participates in processes such as acrosome reaction induction, sperm binding, protection of the oviductal embryo, and may be involved in speciation. In eutherian mammals, this coat is formed of three or four glycoproteins (ZP1–ZP4). While Mus musculus has been used as a model to study the ZP for more than 35 years, surprisingly, it is the only eutherian species in which the ZP is formed of three glycoproteins Zp1, Zp2, and Zp3, Zp4 being a pseudogene. Zp4 was lost in the Mus lineage after it diverged from Rattus, although it is not known when precisely this loss occurred. In this work, the status of Zp4 in several murine rodents was tested by phylogenetic, molecular, and proteomic analyses. Additionally, assays of cross in vitro fertilization between three and four ZP rodents were performed to test the effect of the presence of Zp4 in murine ZP and its possible involvement in reproductive isolation. Our results showed that Zp4 pseudogenization is restricted to the subgenus Mus, which diverged around 6 MYA. Heterologous in vitro fertilization assays demonstrate that a ZP formed of four glycoproteins is not a barrier for the spermatozoa of species with a ZP formed of three glycoproteins. This study identifies the existence of several mouse species with four ZPs that can be considered suitable for use as an experimental animal model to understand the structural and functional roles of the four ZP proteins in other species, including human.

Evolutionary history of the subgenus Mus in Eurasia with special emphasis on the House Mouse Mus musculus

Elucidation of the evolutionary history of the subgenus Mus, including the House Mouse Mus musculus, is essential to understanding species diversification mechanisms in the Indomalayan region, which is a global biodiversity hotspot. In terms of interspecific relationships, the topography of India, Myanmar, and other Southeast Asian regions has been proposed to explain the speciation process and ecological niche diversification followed by range overlap after speciation. Recent research into mitochondrial DNA clocks has created the opportunity to reconstruct the detailed dynamics of M. musculus as affected by human activity. The resultant evolutionary scenarios are in good accordance with archaeological evidence observed in Asia, especially in China, Korea, and Japan.

Molecular Characterization of Species of the Subgenus Mus from Myanmar.

The species composition and genetic diversity of the subgenus Mus in Myanmar are not yet fully understood. In this study, mice were trapped in rural areas near the Ayeyarwady River basin, spanning five Myanmar cities from north to south: Mandalay, Bagan, Magway, Pyay, and Yangon. Mitochondrial cytochrome b (Cytb) and nuclear melanocortin 1 receptor (Mc1r) gene sequences were determined for mice sampled and revealed a widespread occurrence of Mus nitidulus in central Myanmar in addition to its previously known occurrence in the Yangon district of southern Myanmar. Analyses of Cytb revealed two haplogroups with a genetic distance of 2.0%, suggestive of divergence several hundred thousand years ago. Mus caroli and M. musculus were confined to Yangon and Mandalay/Bagan/Magway, respectively. Mice collected from a locality on the eastern side of the Ayeyarwady River in Pyay were identified using Cytb and Mc1r sequences as M. fragilicauda, which was previously identified only in Laos and Thailand. The species M. booduga and M. cervicolor previously predicted to be common in the study area were not found. These findings elucidate the species and genetic diversity of the subgenus Mus in the Indo-Malayan Region.

The complete mitochondrial genome of the servant mouse, Mus famulus

In this article we report the complete mitochondrial genome of the servant mouse, Mus famulus for the first time. The genome size is 16,291 bp. The mitogenome contained a total of 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and 1 control region. The base composition was A (34.4%), C(24.1%), G (12.2%), and T(29.3%), indicating that the percentage of A and T (63.7%) was higher than that of G and C. Most of these genes were distributed on the H-strand, except for the ND6 subunit gene and eight tRNA genes. A phylogenomic analysis of the 10 complete chloroplast genomes supports that M. famulus is a member of the subgenus Mus.

Evolution of the structure and composition of house mouse satellite DNA sequences in the subgenus Mus (Rodentia: Muridea): a cytogenomic approach

The composition and orientation of the house mouse satellite DNA sequences (minor, major, TLC) were investigated by a FISH and CO-FISH approach in 11 taxa belonging to three clades of the subgenus Mus. Using a phylogenetic framework, our results highlighted two distribution patterns. The TLC satellite, the most recently discovered satellite, was present in all clades but varied quantitatively among species. This distribution supported its appearance in the ancestor of the subgenus followed by independent evolution in species of each clade. In contrast, the minor and major satellites occurred in only two clades of the subgenus indicating the simultaneous and recent amplification of these sequences. In addition, although qualitative differences in the composition and orientation of the satellite sequences were observed among the taxa, none of the features studied were unique to the house mouse and could account for the extensive chromosomal plasticity evidenced in Mus musculus domesticus.

The telocentric tandem repeat at the p-arm is not conserved in Mus musculus subspecies

Mouse chromosomes, with the exception of the Y chromosome, are telocentric. The telomere at the p-arm is separated from the centromere by the tL1 sequence and TLC tandem repeats. A previous report showed that the TLC array was also conserved in other strains of the subgenus Mus. These results suggest that the TLC arrays promote the stable evolutionary maintenance of a telocentric karyotype in the subgenus Mus. In this study, we investigated the degree of conservation of TLC arrays among a variety of wild-derived inbred strains, all of which are descendants of wild mice captured in several areas of the world. Genomic PCR analysis indicates that the sequential order of telomere-tL1 is highly conserved in all strains, whereas tL1-TLC is not. Next, Southern blot analysis of DNAs isolated from a panel of mouse subspecies showed both Mus musculus domesticus and Mus musculus castaneus subspecies possess TLC arrays. Unexpectedly, this repeat appears to be lost in almost all Mus musculus musculus and Mus musculus molossinus subspecies, which show a clear geographic divide. These results indicate that either other unknown sequences were replaced by the TLC repeat or almost all M. m. musculus and M. m. molossinus subspecies do not have any sequence between the telomere and minor satellites. Our observation suggests that the TLC array might be evolutionarily unstable and not essential for murine chromosomal conformation. This is the first example of the subspecies-specific large genome alterations in mice.

Mus lepidoides(Muridae, Rodentia) of Central Burma is a Distinct Species of Potentially Great Evolutionary and Biogeographic Significance

Mus lepidoides of central Burma (Myanmar) was described 75 years ago but has since been dismissed as a regional variant of the Indian field mouse, M. booduga. DNA sequences of multiple mitochondrial and nuclear genes from recently collected specimens, combined with a fresh morphological reassessment, reaffirm the distinctiveness of M. lepidoides from M. booduga and from all other species of Mus. Mus lepidoides is so distinct in fact that it warrants placement in its own Species Group within subgenus Mus. Molecular and morphological assessments of phylogenetic affinities converge on the exciting possibility that M. lepidoides represents the previously elusive sibling taxon to the Mus musculus Species Group. If confirmed, this relationship would provide the previously missing connection between the main radiation of subgenus Mus in Southeast and South Asia, and the radiation of the M. musculus Species Group in western Asia and Europe. We speculate that a common ancestor of M. lepidoides and the M. musculus Species Group occupied a continuous but episodic tract of xeric habitat that linked central Burma with northern India at various times during the late Pliocene and Quaternary. Further molecular and cytogenetic studies on the phylogenetic position of M. lepidoides clearly represent a high priority in mouse research.

Evolution of Duplicated -Globin Genes and the Structural Basis of Hemoglobin Isoform Differentiation in Mus

The functional diversification of multigene families may be strongly influenced by mechanisms of concerted evolution such as interparalog gene conversion. The beta-globin gene family of house mice (genus Mus) represents an especially promising system for evaluating the effects of gene conversion on the functional divergence of duplicated genes. Whereas the majority of mammalian species possess tandemly duplicated copies of the adult beta-globin gene that are identical in sequence, natural populations of house mice are often polymorphic for distinct two-locus haplotypes that differ in levels of functional divergence between duplicated beta-globin genes, HBB-T1 and HBB-T2. Here, we use a phylogenetic approach to unravel the complex evolutionary history of the HBB-T1 and HBB-T2 paralogs in a taxonomically diverse set of species in the genus Mus. The main objectives of this study were 1) to reconstruct the evolutionary history of the different HBB haplotypes of house mice, 2) to assess the role of recombinational exchange between HBB-T1 and HBB-T2 in promoting concerted evolution, 3) to assess the role of recombinational exchange between HBB-T1 and HBB-T2 in creating chimeric genes, and 4) to assess the structural basis of hemoglobin isoform differentiation in species that possess distinct HBB paralogs. Results of our phylogenetic survey revealed that the HBB-T1 and HBB-T2 genes in different species of Mus exhibit the full range of evolutionary outcomes with respect to levels of interparalog divergence. At one end of the spectrum, the two identical HBB paralogs on the Hbb(s) haplotype (shared by Mus domesticus, Mus musculus, and Mus spretus) represent a classic example of concerted evolution. At the other end of the spectrum, the two distinct HBB paralogs on the Hbb(d), Hbb(p), Hbb(w1), and Hbb(w2) haplotypes (shared by multiple species in the subgenus Mus) show no trace of gene conversion and are distinguished by a number of functionally important amino acid substitutions. Because the possession of distinct HBB paralogs expands the repertoire of functionally distinct hemoglobin isoforms that can be synthesized during fetal development and postnatal life, variation in the level of functional divergence between HBB-T1 and HBB-T2 may underlie important physiological variation within and among species.

Quantitative variation of LINE-1 sequences in five species and three subspecies of the subgenus Mus and in five Robertsonian races of Mus musculus domesticus

The quantitative variation of a conserved region of the LINE-1 ORF2 sequence was determined in eight species and subspecies of the subgenus Mus (M. m. domesticus, M. m. musculus, M. m. castaneus, M. spicilegus, M. spretus, M. cervicolor, M. cookii, M. caroli) and five Robertsonian races of M. m. domesticus. No differences in LINE-1 ORF2 content were found between all acrocentric or Robertsonian chromosome races, whereas the quantitative variation of the LINE-1 ORF2 sequences detected among the eight taxa partly matches with the clades into which the subgenus is divided. An accumulation of LINE-1 ORF2 elements likely occurred during the evolution of the subgenus. Within the Asiatic clade, M. cervicolor, cookii, and caroli show a low quantity of LINE-1 sequences, also detected within the Palearctic clade in M. m. castaneus and M. spretus, representing perhaps the ancestral condition within the subgenus. On the other hand, M. m. domesticus, M. m. musculus and M. spicilegus showed a high content of LINE-1 ORF2 sequences. Comparison between the chromosomal hybridization pattern of M. m. domesticus, which possesses the highest content, and M. spicilegus did not show any difference in the LINE-1 ORF2 distribution, suggesting that the quantitative variation of this sequence family did not involve chromosome restructuring or a preferential chromosome accumulation, during the evolution of M. m. domesticus.

New data on the distribution of Mus spicilegus Petenyi, 1882 (Rodentia, Muridae) and a distinct mtDNA lineage in the southern Balkans

Despite extensive zoogeographical and taxonomical studies in the subgenus Mus, several issues still remain unresolved. In this context, the distribution area of the mound-building mouse, Mus spicilegus, remains undetermined at the southernmost parts of the species’ range, possibly due to low population densities and seasonal character of mound building. The new records from Greece, presented here, significantly expand the knowledge on Mus spicilegus distribution but also reveal eastern Greek populations which are genetically differentiated from all the other Greek and European ones. These results support an additional colonization route to eastern Greece as part of the migration and expansion process of the mound building mouse in Europe.

Genetic differentiation of subspecies of the house mouse Mus musculus and their taxonomic relationships inferred from RAPD-PCR data

Genetic differentiation of six subspecies of the house mouse Mus musculus (Mus musculus musculus. M. m. domesticus, M. m. castaneus, M. m. gansuensis, M. m. wagneri, and M. m. ssp. (bactrianus?) was examined using RAPD-PCR analysis. In all, 373 loci of total length of about 530 kb were identified. Taxon-specific molecular markers were detected and the levels of genetic differences among the subspecies were estimated. Different degree of subspecific genetic differentiation was shown. The most similar subspecies pairs were M. m. castaneus--M. m. domesticus and M. m. musculus--M. m. gansuensis. In our phylogenetic reconstruction, M. m. wagnery proved to be most different from all the other subspecies. Genetic distances between it and other subspecies were two- to threefold higher than those between the "good"' species of the subgenus Mus (e.g., between M. m. musculus and M. spicilegus, M. musculus and M. abbottii). The estimates of genetic similarity and the taxonomic relationships between six house mouse subspecies inferred from RAPD partially conformed to the results based on cytogenetic and allozyme data. However, they were considerably different from phylogenetic reconstructions based on sequencing of the control mtDNA region, which reflects mutual inconsistency of different systems of inheritance.

Rediscovery of Mus nitidulus Blyth (Rodentia: Muridae), an endemic murine rodent of the central basin of Myanmar

A genetically distinct population of mice from south central Myanmar is identified as Mus nitidulus Blyth, a taxon described in 1859 but subsequently treated as a synonym of a more widely distributed Asian mouse—Mus cervicolor Hodgson, 1845. We present molecular sequence data from mitochondrial and nuclear genes which demonstrate that M. nitidulus is distinct from M. cervicolor and from all other species of Mus currently recognized in the Asian region. The molecular data further show that M. nitidulus is a member of the Mus booduga Species Group within subgenus Mus, and thus phylogenetically remote from M. cervicolor. We stabilize the nomenclature of M. nitidulus by designating a lectotype with associated molecular sequence data. We review and illustrate the morphology of M. nitidulus and reassess all previously referred material. Mus nitidulus appears to be confined to the central basin of Myanmar, an area that formerly supported a mosaic of evergreen and deciduous monsoon forests. Today, this region is largely cleared and employed for rainfed rice cultivation. Mus nitidulus is only the second mammal species recorded as endemic to Myanmar. It can be locally abundant in ricefield habitat and is regarded locally as an agricultural pest.

A new endemic species of the subgenus Mus (Rodentia, Mammalia) on the Island of Cyprus

The house mouse (Mus musculus domesticus) and the short-tailed mouse of the eastern Mediterranean area (M. macedonicus) were thought to live sympatrically on Cyprus Island. Recently, a phylogenetic survey has shown that the non-commensal mouse of Cyprus was an unknown sister species of European wild mice. Here, we describe this new species of the genus Mus (Rodentia, Mammalia), namely Mus cypriacus sp. n., based on 19 specimens trapped in the southern part of Cyprus. These animals were first compared to Eurasian species of mice using both molecular genetics (complete D-loop sequences and nuclear gene intron) and cytogenetics to state on its systematic status. Then classical and geometric morphometric analyses on both cranial and dental characters have been performed to compare Mus cypriacus with circum-Mediterranean species and provide diagnositic morphological characters. Genetic data strongly support a sister species relationship of the new species to M. macedonicus, the closest mainland taxon. Morphometric analyses provide satisfying criteria for diagnosis of this species relative to other Mediterranean species. The most obvious phenotypic characteristics are its long tail and the allometric gigantism and shape robustness of its cranial and dental characters compared to other Mediterranean mice. The molecular clock and the history of the murine settlement on Cyprus are congruent and suggest that the common ancestor of M. cypriacus and M. macedonicus arrived on Cyprus during the Middle Pleistocene by a founder event on natural raft. The remoteness of Cyprus through time has prevented introgression from the mainland gene pool, and favoured phenotypic adaptation to competition release, leading to the allopatric speciation of M. cypriacus.

A new endemic species of the subgenus Mus (Rodentia, Mammalia) on the Island of Cyprus

The house mouse (Mus musculus domesticus) and the short-tailed mouse of the eastern Mediterranean area (M. macedonicus) were thought to live sympatrically on Cyprus Island. Recently, a phylogenetic survey has shown that the non-commensal mouse of Cyprus was an unknown sister species of European wild mice. Here, we describe this new species of the genus Mus (Rodentia, Mammalia), namely Mus cypriacus sp. n., based on 19 specimens trapped in the southern part of Cyprus. These animals were first compared to Eurasian species of mice using both molecular genetics (complete D-loop sequences and nuclear gene intron) and cytogenetics to state on its systematic status. Then classical and geometric morphometric analyses on both cranial and dental characters have been performed to compare Mus cypriacus with circum-Mediterranean species and provide diagnositic morphological characters. Genetic data strongly support a sister species relationship of the new species to M. macedonicus, the closest mainland taxon. Morphometric analyses provide satisfying criteria for diagnosis of this species relative to other Mediterranean species. The most obvious phenotypic characteristics are its long tail and the allometric gigantism and shape robustness of its cranial and dental characters compared to other Mediterranean mice. The molecular clock and the history of the murine settlement on Cyprus are congruent and suggest that the common ancestor of M. cypriacus and M. macedonicus arrived on Cyprus during the Middle Pleistocene by a founder event on natural raft. The remoteness of Cyprus through time has prevented introgression from the mainland gene pool, and favoured phenotypic adaptation to competition release, leading to the allopatric speciation of M. cypriacus.

Tspy is nonfunctional in the Mongolian gerbil but functional in the Syrian hamster

The TSPY gene is conserved in placental mammals and encodes the testis-specific protein, Y encoded. Within the testis, TSPY expression is restricted to germ cells, and it is assumed that TSPY plays a role in the proliferation of germ cells. Since it was first discovered in humans, TSPY orthologous gene families have been subsequently characterized in many mammalian lineages. In contrast to the situation in cattle and primates, in which TSPY is organized in a moderately repetitive cluster, including functional members and pseudogenes, a peculiar situation is observed in rodents, in which Tspy has been become low or single copy and degenerated to a pseudogene in some species of the subgenus Mus. We have extended this approach and investigated Tspy gene evolution in the Syrian hamster ( Mesocricetus auratus) and the Mongolian gerbil ( Meriones unguiculatus). Whereas the Syrian hamster Tspy is functionally conserved, organized in multiple copies, and expressed only in testis, the closely related Mongolian gerbil possesses a single-copy pseudogene that is unable to generate a functional transcript. Thus, the Tspy locus has degenerated at least twice at different points of rodent evolution, strongly supporting the hypothesis that the decay of Y-chromosomal genes is an intrinsic evolutionary process. TSPY is the first example of a Y-chromosomal tandem repetitive gene whose decay could be studied in two independent mammalian lineages.

Origin and Evolution of Processed Pseudogenes That Stabilize Functional Makorin1 mRNAs in Mice, Primates and Other Mammals

We investigate the origin and evolution of a mouse processed pseudogene, Makorin1-p1, whose transcripts stabilize functional Makorin1 mRNAs. It is shown that Makorin1-p1 originated almost immediately before the musculus and cervicolor species groups diverged from each other some 4 million years ago and that the Makorin1-p1 orthologs in various Mus species are transcribed. However, Mus caroli in the cervicolor species group expresses not only Makorin1-p1, but also another older Makorin1-derived processed pseudogene, demonstrating the rapid generation and turnover in subgenus Mus. Under this circumstance, transcribed processed pseudogenes (TPPs) of Makorin1 evolved in a strictly neutral fashion even with an enhanced substitution rate at CpG dinucleotide sites. Next, we extend our analyses to rats and other mammals. It is shown that although these species also possess their own Makorin1-derived TPPs, they occur rather infrequently in simian primates. Under this circumstance, it is hypothesized that already existing TPPs must be prevented from accumulating detrimental mutations by negative selection. This hypothesis is substantiated by the presence of two rather old TPPs, MKRNP1 and MKRN4, in humans and New World monkeys. The evolutionary rate and pattern of Makorin1-derived processed pseudogenes depend heavily on how frequently they are disseminated in the genome.

Molecular phylogeny of the genus Mus (Rodentia: Murinae) based on mitochondrial and nuclear data

The genus Mus encompasses at least 38 species divided into four subgenera: Mus, Pyromys, Nannomys and Co-elomys. The subgenus Mus, which comprises the house mouse and related species, is by far the most extensively studied, although the subgenus Nannomys is the most speciose. Although the relationships within the subgenus Mus are rather well characterized, those between subgenera are still unclear. In the present study, phylogenetic analyses of the whole genus were performed using a larger species sample of Nannomys than in previous studies, and a nuclear gene (IRBP) in addition to mitochondrial data (cytochrome b and 12S rRNA). Members of the Acomyinae and Murinae were used as outgroups. Separate and combined analyses were performed with maximum parsimony, maximum likelihood and Bayesian methods, and divergence times were estimated. The results showed that the monophyly of the genus Mus and of each subgenus was strongly supported by the three genes and the combined analysis. The phylogenies derived from the three genes were on the whole congruent; however, several conflicting topologies were observed such as the relationships between the three Asian species of the subgenus Mus (caroli, cervicolor and cookii). Increasing the taxonomic sampling of Nannomys did not satisfactorily improve the resolution of relationships between the four subgenera. In addition, molecular calibrations indicate that the Mus and Nannomys radiation coincided with major environmental changes.

Phylogenetic relationships in the subgenus Mus (genus Mus, family Muridae, subfamily Murinae): examining gene trees and species trees

Over eight kilobases (kb) of sequence from eight genes including two mitochondrial loci, Cyt b and 12S, and six nuclear loci, B2m , Zp3 , Tcp1, Sry, Smcx and Smcy , were used to investigate phylogenetic relationships among 11 taxa representing eight species within the rodent genus Mus . Particular attention was given to discerning relationships among species within the subgenus Mus including members of a Palearctic clade ( M. musculus , M. spicilegus , M. macedonicus and M. spretus ) and members of an Asian clade ( M. caroli , M. cookii and M. cervicolor ), as previous studies using different datasets have produced different topologies for taxa within these two groups. While parsimony analyses of the combined eight-gene dataset yielded a single, fully resolved tree, support values were lower for nodes resolving relationships within the Palearctic and Asian clades than they were elsewhere in the tree. In addition, a maximum likelihood analysis of the same eight-gene dataset yielded different topologies for both the Palearctic and the Asian clades. Both observations are indicative of clade instability. The nature of this instability was explored through a comparison with our previous study in which we included the two mitochondrial loci and only four of the six nuclear genes, and through an analysis of partitioned data, specifically mitochondrial vs. nuclear genes. This study underscores the importance of considering among-site rate variation in phylogeny reconstruction. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 653‐662.

Temporal, spatial, and ecological modes of evolution of Eurasian Mus based on mitochondrial and nuclear gene sequences

We sequenced mitochondrial (cytochrome b, 12S rRNA) and nuclear (IRBP, RAG1) genes for 17 species of the Old World murine genus Mus, drawn primarily from the Eurasian subgenus Mus. Phylogenetic analysis of the newly and previously available sequences support recognition of four subgenera within Mus ( Mus, Coelomys, Nannomys, and Pyromys), with an unresolved basal polytomy. Our data further indicate that the subgenus Mus contains three distinct ‘species groups’: (1) a Mus booduga Species Group, also including Mus terricolor and Mus fragilicauda (probably also Mus famulus); (2) a Mus cervicolor Species Group, also including Mus caroli and Mus cookii; and (3) a Mus musculus Species Group, also including Mus macedonicus, Mus spicilegus, and Mus spretus. Species diversity in Eurasian Mus is probably explicable in terms of several phases of range expansion and vicariance, and by a propensity within the group to undergo biotope transitions. IRBP and RAG1 molecular clocks for Mus date the origin of subgenera to around 5–6 mya and the origin of Species Groups within subgenus Mus to around 2–3 mya. The temporal pattern of evolution among Eurasian Mus is more complex than that within the Eurasian temperate genus Apodemus.