Expression of glucose phosphate isomerase in interspecific hybrid (Mus musculus x Mus caroli) mouse embryos.

Hybrid Mus musculus x Mus caroli embryos were produced by inseminating M. musculus (C57BL/OlaWs) females with M. caroli sperm. Control M. caroli embryos developed more rapidly than did control M. musculus embryos and implanted approximately 1 day earlier. At 1 1/2 days, both the hybrid embryos and those of the maternal species (M. musculus) had cleaved to the 2-cell stage. By 2 1/2 days some of the hybrids were retarded compared to M. musculus, and by 3 1/2 days most were lagging behind. This is consistent with the idea that the rate of development of hybrid embryos declines once it becomes dependent on embryo-coded gene products. We have used this difference in rate of preimplantation development, between hybrid and M. musculus embryos, to try to determine whether the activation of embryonic Gpi-1s genes, that encode glucose phosphate isomerase (GPI-1), is age-related or stage-related. In control M. musculus embryos (both mated and Al groups), the GPI-1AB and GPI-1A allozyme, indicative of paternal gene expression, were detected in 7 of 9 samples of 3 1/2-day compacted morula stage embryos and were seen in all 19 samples of 3 1/2-day blastocysts. In hybrid embryos, these allozymes were detected 1 day later. They were not detected in any 3 1/2-day samples (12 samples of compacted morulae) but were consistently detected at 4 1/2 days (4 samples of blastocysts and 2 samples of uncompacted morulae). Our interpretation of the results is that gene activation in hybrid embryos is stage-specific, rather than age-specific, and probably begins around the 8-cell stage, with detectable levels of enzyme accumulating later. Analysis of GPI-1 electrophoresis indicated that both the paternal (M. caroli) and maternal (M. musculus) Gpi-1s alleles were equally expressed in hybrid embryos and that the paternally derived allele was not activated before the maternally derived allele.     

Gene amplification in a mouse embryo? Double minutes in cell lines independently derived from a Mus musculus x M. caroli fetus

Double minutes (DM) were found to be present in six of seven clones derived from a 16-day female Mus musculus x M. caroli fetus. The DM-positive clones derived from three primary populations independently set up from the fetus, and included clones with an active M. caroli X chromosome as well as clones with an active M. musculus X. The simplest explanation of these findings is that DM were already present in cells of the M. musculus x M. caroli embryo at the time of X chromosome inactivation and persisted during in vivo development and in vitro culture. This suggests that gene amplification occurred in the early embryo, or even the fertilized egg, perhaps because of interactions between components of germ cells contributed by the M. musculus and M. caroli parents. Alternatively, induction may have occurred independently in these lines, requiring that amplification is an unusually common occurrence in cells from interspecific hybrids.     

Chromosome composition of interspecies hybrid embryonic stem cells in mice

Chromosome complements of 20 hybrid clones obtained by fusing Mus musculus embryonic stem cells (ESCs) and Mus caroli splenocytes were studied. The use of two-color fluorescence hybridization in situ with chromosome- and species-specific probes has allowed us to reliably reveal the parental origin of homologs of any chromosome in hybrid cells. Depending on the ratio of parental chromosome homologs, all 20 hybrid clones were separated in several groups ranging from the clones that contain cells that are nearly tetraploid with two diploid sets of M. musculus and single M. caroli chromosomes to clones with a marked predominance of the M. caroli chromosome. In eight hybrid cell clones, we observed the pronounced prevalence of chromosomes of the pluripotent partner over chromosomes of the somatic partner in a ratio of 5: 1 to 3: 1. In other hybrid cell clones, the ratio of M. musculus to M. caroli chromosomes was either equal (1: 1; 2: 2) or with the prevalence of the pluripotent (2: 1) or differentiated (1: 2) partner. In three hybrid cell clones, for the first time, we observed the predominant segregation of ESC-derived pluripotent chromosomes. This might indicate the compensation for the epigenetic differences between parental chromosomes of the ESC and splenocyte origin.     

Genetic analysis of protein variations in Mus musculus using two-dimensional electrophoresis

We have investigated the variation of proteins from crude homogenates of mouse kidneys in several strains of Mus musculus by means of two-dimensional electrophoresis. In this study, we have used the strains C57BL/6J, DBA/2J, CD-1, M. m. castaneus, and M. m. molossinus, as well as offspring from crosses among these strains. Out of the 100 loci screened, we have found nine loci showing interstrain differences. We have been able to identify three proteins as Id-1, Car-2, and Sep-1. The remaining variants are probably new loci in the mouse. Most of the variants (seven) can be mapped to a chromosome. We have found also that differences in the protein pattern as seen on two-dimensional gels are small among subspecies of Mus musculus.     

Multiple independent pseudogene derivations indicate increased instability of the <Emphasis Type="Italic">Mdm2</Emphasis> locus in <Emphasis Type="Italic">Mus caroli</Emphasis>

Under conditions of genomic stress, the Mdm locus in human and in mouse is prone to instability manifested as amplification and oncogenesis. The Mdm2 gene is a known oncogene that is amplified in approximately one-third of sarcomas and whose protein product interacts with the tumor suppressor p53. Concimitant with such gene amplification events is the activation and mobilization of endogenous retroelements, typically through the relaxation of epigenetic controlling mechanisms. Processed pseudogenes, which can be formed through endogenous LINE retroelement activity, may indicate increased genomic instability. We have isolated processed pseudogenes for Mdm2 in Mus caroli DNA, likely formed from independent events in different individuals. This is the first identification and characterization of an Mdm2 pseudogene in any organism. Multiple retrotransposition events are suggested by the variable sequence and genomic structure of the identified pseudogenes across all exons and the 3UTR. The high degree of similarity between the gene and each pseudogene, as well as the lack of evidence for an Mdm2 pseudogene in several other species of Mus, indicate evolutionarily recent retrotransposition events leading to the formation of the Mdm2 pseudogenes in M. caroli. Previous studies on the Mdm2 locus in Mus caroli showed amplification and overexpression of this gene on double minute chromosomes in a Mus musculus × Mus caroli interspecific hybrid. The identification of an Mdm2 retropseudogene within this species further highlights the predisposition to instability for this region of the genome.     

Counterselection on sex chromosomes in the Mus musculus European hybrid zone

The extent to which alleles can disperse across a hybrid zone depends on the selection they are subjected to in the hybrid genetic background or, for those that are selectively neutral, on their ability to escape from the unfavourable environment by recombination. Three markers spanning a 45 cM segment in the center of the X chromosome were used to investigate the degree to which selection against X chromosome linked genes helps to maintain the barrier to gene flow in the hybrid zone between Mus musculus domesticus and M. m. musculus in Denmark. The introgression of all the sex chromosome specific markers was more limited than that of the autosomal enzymes (Idh1, Amy, Gpd1, Pgm1, Es1, Es2, Mpi, Np1, Es10, Sod1) and the mitochondrial DNA. The cline for DXPas2, which is in the center of the X chromosome, is extremely steep and shows that certain genes located in this region are strongly selected against in the hybrid background. The clines of the other two X-linked markers, Hprt and DXPas1, and of the Y chromosome are not as abrupt and all three have similar asymmetric introgression patterns. Although the musculus variants appear to behave in much the same way as those of the autosomal genes, the domesticus variants do not introgress. The results show that X-linked and to a lesser extent Y-linked genes are more strongly selected against in the hybrid genome than the mitochondrial genome or the different autosomal loci. This suggests that co-adapted gene systems involving the sex chromosomes may play an important role in the hybrid breakdown between the two subspecies.     

Syntheses of 2-Isopropyl-4,5-dihydrothiazole and 6-Hydroxy-6-methyl-3-heptanone,Pheromone Components of the Male Mouse,Mus musculus

Syntheses of 2-isopropyl-4,5-dihydrothiazole and 6-hydroxy-6-methyl-3-heptanone, pheromone components of the male mouse, Mus musculus, were achieved to provide sufficient amounts of samples for biological studies.     

Detection of recombinant haplotypes in wild mice (Mus musculus) provides new insights into the origin of Japanese mice

Japanese house mice (Mus musculus molossinus) are thought to be a hybrid lineage derived from two prehistoric immigrants, the subspecies M. m. musculus of northern Eurasia and M. m. castaneus of South Asia. Mice of the western European subspecies M. m. domesticus have been detected in Japanese ports and airports only. We examined haplotype structuring of a 200 kb stretch on chromosome 8 for 59 mice from throughout Eurasia, determining short segments (≈ 370–600 bp) of eight nuclear genes (Fanca, Spire2, Tcf25, Mc1r, Tubb3, Def8, Afg3l1 and Dbndd1) which are intermittently arranged in this order. Where possible we identified the subspecies origin for individual gene alleles and then designated haplotypes for concatenated alleles. We recovered 11 haplotypes among 19 Japanese mice examined, identified either as ‘intact’ haplotypes derived from the subspecies musculus (57.9%), domesticus (7.9%), and castaneus (2.6%), or as ‘recombinant’ haplotypes (31.6%). We also detected recombinant haplotypes unique to Sakhalin. The complex nature of the recombinant haplotypes suggests ancient introduction of all three subspecies components into the peripheral part of Eurasia or complicated genomic admixture before the movement from source areas. ‘Intact’domesticus and castaneus haplotypes in other Japanese wild mice imply ongoing stowaway introductions. The method has general utility for assessing the history of genetic admixture and for disclosing ongoing genetic contamination.     

Phylogeography of Chinese house mice (Mus musculus musculus/castaneus): distribution,routes of colonization and geographic regions of hybridization

House mice (Mus musculus) are human commensals and have served as a primary model in biomedical, ecological and evolutionary research. Although there is detailed knowledge of the biogeography of house mice in Europe, little is known of the history of house mice in China, despite the fact that China encompasses an enormous portion of their range. In the present study, 535 house mice caught from 29 localities in China were studied by sequencing the mitochondrial D‐loop and genotyping 10 nuclear microsatellite markers distributed on 10 chromosomes. Phylogenetic analyses revealed two evolutionary lineages corresponding to Mus musculus castaneus and Mus musculus musculus in the south and north, respectively, with the Yangtze River approximately representing the boundary. More detailed analyses combining published sequence data from mice sampled in neighbouring countries revealed the migration routes of the two subspecies into China: M. m. castaneus appeared to have migrated through a southern route (Yunnan and Guangxi), whereas M. m. musculus entered China from Kazakhstan through the north‐west border (Xinjiang). Bayesian analysis of mitochondrial sequences indicated rapid population expansions in both subspecies, approximately 4650–9300 and 7150–14 300 years ago for M. m. castaneus and M. m. musculus, respectively. Interestingly, the migration routes of Chinese house mice coincide with the colonization routes of modern humans into China, and the expansion times of house mice are consistent with the development of agriculture in southern and northern China, respectively. Finally, our study confirmed the existence of a hybrid zone between M. m. castaneus and M. m. musculus in China. Further study of this hybrid zone will provide a useful counterpart to the well‐studied hybrid zone between M. m. musculus and Mus musculus domesticus in central Europe.     

Polymorphism and linkage for mannosephosphate isomerase in Mus musculus

Electrophoretic variants of the enzyme mannosephosphate isomerase (E.C. 5.3.1.8) (MPI) have been discovered in the mouse. The MPI-IA phenotype was found in Mus castaneus and in the inbred strain MA/J of Mus musculus. Other inbred strains of Mus musculus examined possessed the MPI-1B phenotype. Genetic studies show that the MPI variants segregate as codominant alleles of a single autosomal locus, designated Mpi-1 in linkage group II. The gene order Mod-1-d-Mpi-1 has been established. Human and murine forms of MPI differ and can be detected in in vitro fibroblasts and somatic cell hybrid populations.Supported by GB 18543 of the National Science Foundation, RSA-70-20 of the Connecticut Research Commission, and GM 09966 of the U.S. Public Health Service.     

Selection of Rodent Species Appropriate for mtDNA Transfer to Generate Transmitochondrial Mito-Mice Expressing Mitochondrial Respiration Defects

Previous reports have shown that transmitochondrial mito-mice with nuclear DNA from Mus musculus and mtDNA from M. spretus do not express respiration defects, whereas those with mtDNA from Rattus norvegicus cannot be generated from ES cybrids with mtDNA from R. norvegicus due to inducing significant respiration defects and resultant losing multipotency. Here, we isolated transmitochondrial cybrids with mtDNA from various rodent species classified between M. spretus and R. norvegicus, and compared the O₂ consumption rates. The results showed a strong negative correlation between phylogenetic distance and reduction of O₂ consumption rates, which would be due to the coevolution of nuclear and mitochondrial genomes and the resultant incompatibility between the nuclear genome from M. musculus and the mitochondrial genome from the other rodent species. These observations suggested that M. caroli was an appropriate mtDNA donor to generate transmitochondrial mito-mice with nuclear DNA from M. musculus. Then, we generated ES cybrids with M. caroli mtDNA, and found that these ES cybrids expressed respiration defects without losing multipotency and can be used to generate transmitochondrial mito-mice expressing mitochondrial disorders.     

Visible and “cryptic” segregation of parental chromosomes in embryonic stem hybrid cells

Chromosome segregation of the parental chromosomes was studied in 20 interspecific hybrid clones obtained by fusion of Mus musculus embryonic stem cells with Mus caroli splenocytes. FISH analysis with labeled species specific probes and microsatellite markers was used for identification of the parental chromosomes. Cytogenetic analysis has shown significant intra- and interclonal variability in chromosome numbers and ratios of the parental chromosomes in the hybrid cells: six clones contained all M. caroli chromosomes, nine clones showed moderate segregation of M. caroli chromosomes (from 1 to 7), and five clones showed extensive loss of M. caroli chromosomes (from 12 to complete loss of all M. caroli autosomes). Both methods demonstrated cryptic segregation of the somatic partner chromosomes. For instance, five clones with near-tetraploid chromosome sets contained only few M. caroli chromosomes (from 1 to 8). The data obtained suggest that the tetraploid chromosome set per se is not a sufficient criterion for conclusion on the absence of chromosome loss in the hybrid cells. Note that cryptic chromosome segregation occurred at a high frequency in the examined hybrid clones. Thus, cryptic segregation should be borne in mind for assessing pluripotency and genome reprogramming of embryonic stem hybrid cells.__________Translated from Ontogenez, Vol. 36, No. 2, 2005, pp. 151–158.Original Russian Text Copyright © 2005 by Pristyazhnyuk, Temirova, Menzorov, Kruglova, Matveeva, Serov.     

The chromosomal distribution of the major and minor satellite is not conserved in the genusMus

The cytological distribution of the major and minor satellite first identified inMus musculus was studied in the karyotypes of three related subspecies and two other species of the genusMus. Both the major and minor satellite showed species dependent hybridization patterns. The major satellite is confined to the centromere region inM. musculus and related subspecies. However, inM spretus andM. caroli, the chromosomal arm regions contain this sequence class. In contrast the minor satellite is found at the kinetochore region inM. musculus and related subspecies but is distributed throughout the entire centromeric domain inM. spretus and appears to be excluded from the chromosomes ofM. caroli. There is an apparent correlation between the chromosomal location of these satellites and their phylogenetic relationship. Determination of the biological roles of the major and minor satellites fromM. musculus must take into account their differential chromosomal distribution in otherMus species.     

Quantitative analysis of mid-gestation mouse aggregation chimaeras: non-random composition of the placenta

Mouse chimaeras were produced by aggregating eight-cell embryos from two different F₂ matings, abbreviated to AF₂ and BF₂ respectively: (C57BL/ OIa.AKR-Gpi-1s ^a, c/Ws female × BALB/c male)F₂ and (C57BL/Ws female × CBA/Ca male)F₂. Quantitative electrophoresis of glucose phosphate isomerase (GPI-1) was used to estimate the proportions of the two cell populations in different tissues of the 12 day chimàeric conceptuses, with the % GPI-1A indicating the percentage of cells derived from the AF₂ embryos. The % GPI-1A was found to be highly positively correlated within the primitive ectoderm lineage (between the fetus, amnion and yolk sac mesoderm) and within the primitive endoderm lineage (between the yolk sac endoderm and the parietal endoderm) but no correlation (either positive or negative) was seen between the two lineages. This confirms the results of a previous,study of chimaeras made between partially congenic strains and suggests the original conclusions have general validity. The % GPI-1A in the placenta was corrected for the expected contribution of maternal GPI-1, based on control experiments involving transfer of homozygous Gpi-1s ^b /Gpi-1s ^b embryos to the uteri of Gpi-1s ^a /Gpi-1s ^a pseudopregnant females. The corrected % GPI- lA in the placenta was positively correlated with that in each of the three primitive ectoderm derivatives. This suggests either (1) exchange of cells between the polar trophectoderm and the underlying part of the inner cell mass that forms the primitive ectoderm or (2) cells are incompletely mixed in the chimaeric blastocyst and patches of AF₂ and BF₂ cells straddle the boundary between the polar trophectoderm and the underlying primitive ectoderm. The second explanation does not imply the existence of shared developmental lineages between trophectoderm and primitive ectoderm in non-chimaeric embryos. Unlike that of any other tissue, the distribution of placental GPI-1A was U-shaped; in 17/28 placenta samples the proportion of the minor component was 10% or less. This suggests that the placental trophoblast is derived from a small number of coherenct clones of polar trophectoderm cells (either a small number of polar trophectoderm cells or a larger number if the two cell populations are not finely intermingled). Thus, although as a population the placentas of chimaeric conceptuses are balanced with respect to the % GPI-1A (mean close to 50%), individually most placentas are extremely unbalanced in their chimaeric composition (< 10% or > 90% GPI-IA). This non-random composition of the chimaeric placentas is in contrast to the widely held assumption that the distribution of cells in chimaeric conceptuses is normally random. Correspondence to: J.D. West     

Expression of glucose-phosphate isomerase in relation to growth of the mouse oocyte in vivo and in vitro

The activity of the enzyme glucose-phosphate isomerase (GPI-1) in mouse oocytes is subject to regulation by the cis-acting gene Gpi-lt^a. Electrophoretic analysis of oocytes from 9- and 10-day-old mice showed that oocyte-specific regulation of GPI-1 is not observed in germ cells that have not started to grow (20 μm diameter) but appears as soon as oocyte growth begins (30 μm or larger). Three in vitro culture systems were used to examine the relation of GPI-1 expression to oocyte growth: culture of intact neonatal ovaries, and co-culture of dissociated oocytes and somatic cells from neonatal and from 13-day foetal ovaries. In all three systems modification of GPI-1 expression always occurred when oocyte growth began, showing that the presence of a normal follicle is not necessary for the expression of the gene Gpi-lt^a.     

Gene flow of unique sequences between Mus musculus domesticus and Mus spretus

Allelic diversity has been examined from a variety of Mus musculus subspecies and Mus spretus strains by sequencing at a 453-bp unique sequence locus. One M. m. domesticus classic inbred strain, C57BL/KsJ, contained a sequence identical to that in the M. spretus wild-derived inbred strain SEG, and other wild M. spretus isolates. Such a result should have been precluded by the expected divergence between the species unless there has been interspecies gene flow. Examination of C57BL/KsJ for M. spretus-specific repetitive sequences shows that it is neither a mis-identified spretus strain nor a domesticus/spretus hybrid. Thus, in addition to the previously reported presence of small amounts of Mus spretus-specific repetitive DNA in M. m. domesticus, there is a detectable flow of unique sequence between the two species. There was also ancestral polymorphism observed among the spretus alleles. The difficulty of distinguishing ancestral polymorphism from horizontal transfer is discussed. Received: 14 May 1999 / Accepted: 5 November 1999     

A molecular characterization of the charismatic Faroe house mouse

Faroe house mice are a ‘classic’ system of rapid and dramatic morphological divergence highlighted by J. S. Huxley during the development of the Modern Synthesis. In the present study, we characterize these charismatic mice using modern molecular techniques, examining specimens from all Faroe islands occupied by mice. The aims were to classify the mice within the modern house mouse taxonomy (i.e. as either Mus musculus domesticus or Mus musculus musculus) using four molecular markers and a morphological feature, and to examine the genetic diversity and possible routes of colonization using mitochondrial (mt) control region DNA sequences and microsatellite data (15 loci). Mice on the most remote islands were characterized as M. m. domesticus and exhibited exceptionally low genetic diversity, whereas those on better connected islands were more genetically diverse and had both M. m. musculus and M. m. domesticus genetic elements, including one population which was morphologically M. m. musculus‐like. The mtDNA data indicate that the majority of the mice had their origins in south‐western Norway (or possibly southern Denmark/northern Germany), and probably arrived with the Vikings, earlier than suggested by Huxley. The M. m. musculus genetic component appears to derive from recent mouse immigration from Denmark. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 471–482.     

Norwegian house mice (Mus musculus musculus/domesticus): distributions, routes of colonization and patterns of hybridization

We investigated the distributions and routes of colonization of two commensal subspecies of house mouse in Norway: Mus musculus domesticus and M. m. musculus. Five nuclear markers (Abpa, D11 cenB2, Btk, SMCY and Zfy2) and a morphological feature (tail length) were used to differentiate the two subspecies and assess their distributions, and mitochondrial (mt) D‐loop sequences helped to elucidate their colonization history. M. m. domesticus is the more widespread of the two subspecies, occupying the western and southern coast of Norway, while M. m. musculus is found along Norway’s southeastern coast and east from there to Sweden. Two sections of the hybrid zone between the two subspecies were localized in Norway. However, hybrid forms also occur well away from that hybrid zone, the most prevalent of which are mice with a M. m. musculus‐type Y chromosome and an otherwise M. m. domesticus genome. MtDNA D‐loop sequences of the mice revealed a complex phylogeography within M. m. domesticus, reflecting passive human transport to Norway, probably during the Viking period. M. m. musculus may have colonized earlier. If so, that leaves open the possibility that M. m. domesticus replaced M. m. musculus from much of Norway, with the widely distributed hybrids a relict of this process. Overall, the effects of hybridization are evident in house mice throughout Norway.