Two types of mouse (Mus musculus domesticus) Y chromosomes in Quebec.

A Y chromosomal repetitive sequence identified two types of Y chromosomes in mice (Mus musculus domesticus) caught near Ste. Anne de Bellevue, Quebec. One type is apparently identical to the Y chromosome found in Maryland, Delaware, and California, whereas the other type is similar, but not identical, to the Y chromosome present in M.m. poschiavinus, an Alpine race of M.m. domesticus. These findings suggest that the domesticus Y chromosome is highly polymorphic and thus useful for elucidating the relationships among American and European house mouse populations.     

C57BL/6J-T-associated sex reversal in mice is caused by reduced expression of a Mus domesticus Sry allele

C57BL/6J-T-associated sex reversal (B6-TAS) in XY mice results in ovarian development and involves (1) hemizygosity for Tas, a gene located in the region of Chromosome 17 deleted in T(hp) and T(Orl), (2) homozygosity for one or more B6-derived autosomal genes, and (3) the presence of the AKR Y chromosome. Here we report results from experiments designed to investigate the Y chromosome component of this sex reversal. Testis development was restored in B6 T(Orl)/+ XY(AKR) mice carrying a Mus musculus Sry transgene. In addition, two functionally different classes of M. domesticus Sry alleles were identified among eight standard and two wild-derived inbred strains. One class, which includes AKR, did not initiate normal testis development in B6 T(Orl)/+ XY mice, whereas the other did. DNA sequence analysis of the Sry ORF and a 5' 800-bp segment divided these inbred strains into the same groups. Finally, we found that Sry is transcribed in B6 T(Orl)/+ XY(AKR) fetal gonads but at a reduced level. These results pinpoint Sry as the Y-linked component of B6-TAS. We hypothesize that the inability of specific M. domesticus Sry alleles to initiate normal testis development in B6 T(Orl)/+ XY(AKR) mice results from a biologically insufficient level of Sry expression, allowing the ovarian development pathway to proceed.     

Sex reversal in the mouse (Mus musculus) is caused by a recurrent nonreciprocal crossover involving the X and an aberrant Y chromosome

Satellite DNA (Bkm) from the W sex-determining chromosome of snakes, which is related to sequences on the mouse Y chromosome, has been used to analyze the DNA and chromosomes of sex-reversed (Sxr) XXSxr male mice. Such mice exhibit a male-specific Southern blot Bkm hybridization pattern, consistent with the presence of Y-chromosome DNA. In situ hybridization of Bkm to chromosomes of XXSxr mice shows an aberrant concentration of related sequences on the distal terminus of a large mouse chromosome. The XYSxr carrier male, however, shows a pair of small chromosomes, which are presumed to be aberrant Y derivatives. Meiosis in the XYSxr mouse involves transfer of chromatin rich in Bkm-related DNA from the Y-Y1 complex to the X distal terminus. We suggest that this event is responsible for the transmission of the Sxr trait.     

Genetic analysis of the hybridization zone between two subspecies Mus musculus domesticus and Mus musculus musculus in Bulgaria

The hybrid zone between the two subspecies of mice Mus musculus domesticus and Mus musculus musculus, which has been studied extensively in Denmark, crosses Europe to the Black Sea through the Alps and the Balkans. Two hundred and seventy-nine animals were captured in 22 localities along a transect across the Balkans. The animals were characterized for seven diagnostic nuclear loci by protein electrophoresis and by restriction pattern analysis of their mitochondrial DNA. The nuclear data show a sharp transition between the two subspecies, most of the variations in allele frequencies (from 0.9 to 0.1) occurring within a 36-km section of the transect. The introgression varies from one locus to the other and is more pronounced, in terms of distance, in M. m. musculus territory. Mitochondrial DNA introgression is important but occurs in one direction only, i.e. from M. m. musculus to M. m. domesticus, while a cytoplasmic transfer from M. m. domesticus to M. m. musculus has been reported. A previous study showed that no Y chromosome introgression occurs. The different behaviour of these three types of markers could be due to the interaction between selection against hybrid genomes and meiotic recombination. Objectively, it would appear that the genes that can introgress are neutral or nearly so and have been separated from deleterious genes they were linked to by recombination. This could explain the differential introgression between autosomal loci. The mitochondrial and Y chromosomes undergo no or very little recombination and each is transmitted as a whole. Their degree of introgression is thus indicative of the intensity of selection resulting from the amount of functional differentiation between the two taxa, which seems to be strong for the Y chromosome and weak for mitochondrial DNA. We propose that the asymmetry of nuclear introgression is due to different population structures. As M. m. musculus is relatively less structured, the rapid spreading of introgressed genes would be favoured. Such a scheme, however, can hardly account for the unidirectionality of the mitochondrial flow, which could be due to sex-dependent behaviour.     

Mitochondrial DNA in the hybrid zone between Mus musculus musculus and Mus musculus domesticus: a comparison of two transects

We studied mtDNA introgression across the contact zone between Mus musculus musculus and M. m. domesticus in two independent transects in the Czech Republic and Bavaria, Germany. A total of 1270 mice from 98 localities in the Czech transect and 456 mice from 41 localities in the Bavarian transect were examined for presence or absence of a Bam HI restriction site in the mt-Nd1 gene. Using this simple mtDNA marker, variants that belonged to the M. m. domesticus lineage (presence of restriction site) could be unequivocally distinguished from those belonging to the M. m. musculus lineage (absence of restriction site). The extent of introgression of mtDNA, three autosomal allozymes and the X chromosome was compared. The introgression of X markers was more limited than was that of the allozymes and mtDNA. In the Czech transect, the centre for the mtDNA cline was shifted about 3.6 km to the west relative to the X chromosome cline, with asymmetric introgression from M. m. musculus to M. m. domesticus . Interestingly, in the Bavarian transect, the centre of the mtDNA cline was shifted about 10.9 km to the east relative to the X chromosome cline, with asymmetric introgression from M. m. domesticus to M. m. musculus, opposite in direction to that observed in the Czech transect.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 363–378.     

Adaptative evolution of the Vkorc1 gene in Mus musculus domesticus is influenced by the selective pressure of anticoagulant rodenticides

Anticoagulant rodenticides are commonly used to control rodent pests worldwide. They specifically inhibit the vitamin K epoxide reductase (VKORC1), which is an enzyme encoded by the Vkorc1 gene, involved in the recycling of vitamin K. Therefore, they prevent blood clotting. Numerous mutations of Vkorc1 gene were reported in rodents, and some are involved in the resistant to rodenticides phenotype. Two hundred and sixty‐six mice tails were received from 65 different locations in France. Coding sequences of Vkorc1 gene were sequenced in order to detect mutations. Consequences of the observed mutations were evaluated by the use of recombinant VKORC1. More than 70% of mice presented Vkorc1 mutations. Among these mice, 80% were homozygous. Contrary to brown rats for which only one predominant Vkorc1 genotype was found in France, nine missense single mutations and four double mutations were observed in house mice. The single mutations lead to resistance to first‐generation antivitamin K (AVKs) only and are certainly associated with the use of these first‐generation molecules by nonprofessionals for the control of mice populations. The double mutations, probably obtained by genetic recombination, lead to in vitro resistance to all AVKs. They must be regarded as an adaptive evolution to the current use of second‐generation AVKs. The intensive use of first‐generation anticoagulants probably allowed the selection of a high diversity of mutations, which makes possible the genetic recombination and consequently provokes the emergence of the more resistant mutated Vkorc1 described to date.     

Distribution of the molossinus allele of Sry, the testis-determining gene, in wild mice

When the Y chromosome of the laboratory inbred mouse strain C57BL/6 (B6) is replaced by the Y of certain strains of Mus musculus domesticus, testis determination fails and all XY fetuses develop either as hermaphrodites or XY females (XY sex reversal). This suggests the presence of at least two alleles of Sry, the male-determining gene on the Y:M. m. domesticus and B6. The B6 Y chromosome is derived from the Japanese house mouse, M. m. molossinus and therefore carries a molossinus Sry allele. As a first step to determine how the molossinus Sry allele evolved, its distribution pattern was determined in wild mice. The cumulative data of 96 M. musculus samples obtained from 58 geographical locations in Europe, North Africa, and Asia show the molossinus Sry allele is restricted to Japan and the neighboring Asian mainland and confirm that Japanese M. m. molossinus mice were derived in part from a race of M. m. musculus from Korea or Manchuria. Sry polymorphisms, as illustrated by the molossinus Sry allele, can serve as molecular markers for studies on the evolution of wild M. musculus populations and can help determine the role sex determination plays in speciation.      

Behavioural discrimination among chromosomal races of the house mouse (Mus musculus domesticus)

This work is concerned with the extent of behavioural discrimination between three chromosomal races of the house mouse (the standard 40-chromosome race and a 32- and 36-chromosome races) found in the vicinity of a hybrid zone in northern Scotland. Mice were investigated for several elements of their social behaviour. Within-population dyadic encounters did not show consistent behavioural differences attributable to karyotype among five populations (two standard race, two 36-chromosome race, one 32-chromosome race). Between-population dyadic encounters revealed significant differences between three populations. The standard population examined appeared to be the most “open” to foreigners, the 32-chromosome population the most “closed” while the 36-chromosome mice displayed an intermediate response. Differences in behaviour displayed during between-population as compared to within-population dyadic encounters revealed the occurrence of behavioural discrimination between populations. The implication of these results on the dynamics of the hybrid zone are discussed.     

Intermittent stimulation and acceleration of puberty by urinary chemosignals in female mice (Mus musculus domesticus)

A sequence of 17 experiments was used to test the effects of intermittent stimulation with urinary chemosignals on the age of puberty in young female mice. The three chemosignals tested all accelerate the age of sexual maturation: urine from adult males, urine from females in estrus, and urine from females that are pregnant or lactating. The basic technique involved presenting the prepubertal females with 'Nestlets' on which the urine was placed. The 'Nestlets' were placed in the cages of the test females for a 15-min period, removed for a variable period, and then replaced in the cage for 15 min. In this manner it was possible to vary the number of exposures, the total length of exposure, and the total time period over which the exposures occurred. Control procedures, involving exposures of young females to cotton squares with water rather than urine placed upon them, resulted in no alterations in puberty relative to untreated females. For mice exposed to the urine-treated cotton squares, acceleration of puberty occurred with less total stimulus-exposure time when the stimulus was presented in short exposures over a number of hours than in previous investigations when the exposure to the urinary chemosignal occurred in a single block of time of one or two hours. For each of the three acceleratory chemosignals, there was a diminution of acceleratory effect when the ratio of total stimulus-exposure time to total exposure time grew smaller. This diminution was more pronounced for urine from pregnant or lactating females than for urine from males or from females in estrus.(ABSTRACT TRUNCATED AT 250 WORDS)