Genetic variation in mouse apolipoprotein A-IV due to insertion and deletion in a region of tandem repeats.

We have detected three unique apolipoprotein A-IV (apoA-IV) charge isoforms in strains of commensal mice. The cDNA sequences for one representative of each isoform (Mus domestesticus strains C57BL/6J and 129/J and Mus castaneus) revealed a polymorphism within a series of four imperfect repeats encoding the sequence Glu-Gln-Ala/Val-Gln. Insertions or deletions of 12 nucleotides within this repetitive region have given rise to three genotypes characterized by three (129), four (C57BL/6), or five (M. castaneus) copies of the repeat unit. To ascertain the extent of this variation among other species of the Mus genus, we sequenced this region of apoA-IV cDNAs from eight additional M. domesticus inbred strains and from five wild-derived Mus species. All eight additional M. domesticus strains examined had four repeat units, as found in C57BL/6. Among wild-derived mice, however, one species (Mus spretus) had three repeats, two species (Mus cookii and Mus cervicolor) had four repeats, and two species (Mus hortulanus and Mus minutoides) had five repeats. A lack of correlation between the number of repeat units and the phylogeny of Mus species indicates that independent mutations may have occurred throughout the evolution of specific mouse lineages. We suggest that the repetitive nature of the polymorphic sequence may predispose this region to slippage errors during DNA replication, resulting in frequent deletion/insertion mutations.     

Genome comparison in the genus Mus: a study with B1, MIF (mouse interspersed fragment), centromeric, and Y-chromosomal repetitive sequences

Using four repetitive sequences, we compared DNAs isolated from Mus caroli, M. cookii, M. hortulanus, M. musculus, M. pahari, M. saxicola, and M. spretus. Except for B1, these probes showed species-specific hybridization patterns. Mouse interspersed fragment (MIF) sequences were present in all species examined, but those defined by the 1.3-kb EcoR1 band were fewer in M. pahari and M. saxicola than in the other species. The Y-chromosomal probe showed male-specific accumulation only in M. hortulanus, M. musculus, and M. spretus, which are known to be closely related. The genetic difference between M. spretus and the other two species (M. hortulanus and M. musculus) was clearly demonstrated by a M. musuclus centromeric sequence that hybridized strongly to M. hortulanus and M. musculus DNA but was underrepresented in the genome of M. spretus. These results may suggest the usefulness of these repetitive sequences in the classification of Mus species that display only subtle morphological differences.     

Developmental expression, cellular localization, and testosterone regulation of alpha 1-antitrypsin in Mus caroli kidney

alpha 1-Antitrypsin (alpha 1-protease inhibitor), an essential plasma protein, is synthesized predominantly in the liver of all mammals. We have previously shown that Mus caroli, a Southeast Asian mouse species is exceptional in that it expresses abundantly alpha 1-antitrypsin mRNA and polypeptide, in the kidney as well as the liver (Berger, F.G., and Baumann, H. (1985) J. Biol. Chem. 260, 1160-1165) providing a unique model for examination of the evolution of genetic determinants of tissue-specific gene expression. In the present paper, we have further characterized alpha 1-antitrypsin expression in M. caroli. The extrahepatic expression of alpha 1-antitrypsin is limited to the kidney, specifically within a subset of the proximal tubule cells. The developmental pattern of alpha 1-antitrypsin mRNA expression in the kidney differs from that in the liver. In the kidney, alpha 1-antitrypsin mRNA is present at only 2-4% adult level at birth and increases very rapidly to adult level during puberty between 26 and 36 days of age. There are no significant changes in liver alpha 1-antitrypsin mRNA levels during this period. Testosterone, while having only modest affects on alpha 1-antitrypsin mRNA accumulation in the adult kidney, causes a 20-fold induction of the mRNA in the pre-pubertal kidney. This suggests that the increase in alpha 1-antitrypsin mRNA expression during puberty is testosterone mediated. Southern blot analyses of Mus domesticus and M. caroli genomic DNA and a cloned M. caroli alpha 1-antitrypsin genomic sequence, indicate that a single alpha 1-antitrypsin gene exists in M. caroli, whereas multiple copies exist in M. domesticus. These data show that the alteration in tissue specificity of alpha 1-antitrypsin mRNA accumulation that has occurred during Mus evolution is associated with distinctive developmental and hormonally regulated expression patterns.     

A Repeated Segment on the Mouse Y Chromosome Is Composed of Retroviral-Related, Y-Enriched and Y-Specific Sequences

We report the isolation and characterization of two recombinant clones containing DNA derived from the Y chromosome of the C57BL/10 inbred mouse strain. Both clones were isolated from a lambda phage library derived from a partial EcoRI digest of C57BL/10 male DNA using the murine retrovirus M720. Characterization of these clones showed they were derived from a repeated segment present on the C57BL/10J Y chromosome that contains sequences found elsewhere in the genome. In addition, one clone contained a sequence, designated YB10, that is unique to the Y chromosome and present in approximately 500 copies on the C57BL/10J Y chromosome. Analysis of Southern blots containing DNAs prepared from females and males of representative species from four subgenera of Mus probed with pYB10 and the 3'LTR from one of the Y-associated retroviruses (MuRVY) revealed that, with the exception of a single fragment observed in both female and male DNA of Mus saxicola, hybridization to pYB10 was observed only to male DNA of the species Mus spretus, Mus hortulanus, Mus musculus, Mus domesticus and Mus abbotti. In addition, the pattern and intensity of hybridization to YB10 and the MuRVY-LTR indicated that sequence of divergence was followed by amplification of Y chromosome sequences containing YB10 and MuRVY. The divergence and amplification occurred separately in each of the ancestral lineages leading to M. spretus, M. hortulanus, M. abbotti, M. musculus and M. domesticus. We suggest that acquisition and amplification of DNA sequences by the mammalian Y chromosome has contributed to its evolution and may imply that the mammalian Y chromosome is evolving at a faster rate than the rest of the genome.     

Evolution of androgen-regulated mRNA expression in mouse kidney

To gain information on the evolution of mammalian gene expression patterns, we studied the androgen-inducible expression of three kidney mRNAs in several mouse species (genus Mus). The RP2, ornithine decarboxylase, and beta-glucuronidase mRNAs have each evolved independently, in that the pattern of variation among species is unique for each. This suggests a role for gene-specific, cis-acting genetic elements. Relationships between the regulatory phenotypes and the species phylogeny suggest that the variations in hormone-inducible mRNA expression were generated by a series of independent mutations that occurred in specific lineages, resulting in modifications of the progenitor phenotype. Alternatively, the variations may have preexisted within the progenitor population as polymorphisms that were fixed during establishment of individual lineages. Thus, significant alterations in the androgen-regulated mRNA phenotype have occurred either prior to or during speciation within the Mus genus. These alterations are presumed to be in regulatory sequences that control the expression of the corresponding genes and their response to testosterone; as such, they should be useful in further studying the genetic determinants of gene expression and its evolution.      

Reduced nucleotide variability at an androgen-binding protein locus (Abpa) in house mice: evidence for positive natural selection.

Previous work has shown that the gene for the alpha subunit of androgen-binding protein, Abpa, may be involved in premating isolation between different subspecies of the house mouse, Mus musculus. We investigated patterns of DNA sequence variation at Abpa within and between species of mice to test several predictions of a model of neutral molecular evolution. Intraspecific variation among 10 Mus musculus domesticus alleles was compared with divergence between M. m. domesticus and M. caroli for Abpa and two X-linked genes, Glra2 and Amg. No variation was observed at Abpa within M. m. domesticus. The ratio of polymorphism to divergence was significantly lower at Abpa than at Glra2 and Amg, despite the fact that all three genes experience similar rates of recombination. Interspecific comparisons among M. m. domesticus, Mus musculus musculus, Mus musculus castaneus, Mus spretus, Mus spicilegus, and Mus caroli revealed that the ratio of nonsynonymous substitutions to synonymous substitutions on a per-site basis (Ka/Ks) was generally greater than one. The combined observations of no variation at Abpa within M. m: domesticus and uniformly high Ka/Ks values between species suggest that positive directional selection has acted recently at this locus.     

Genetic differences in the histochemically defined structure of oligosaccharides in mice

A wide range of tissues from three interfertile species of mice and an interspecific hybrid was examined with lectins conjugated to peroxidase to localize specifically glycoconjugates containing terminal alpha-N-acetylgalactosamine, alpha-galactose, and alpha-fucose, and the terminal disaccharide galactose-(beta 1----3)-N-acetylgalactosamine. This battery of lectins disclosed marked heterogeneity of glycoconjugates in different histological sites in a given animal and even between cells in a presumably homogeneous cell population within an organ. No variation with any lectin was observed between individuals of two closely related inbred strains of Mus domesticus at any specific histological or cytological site. In contrast, littermates of an outbred strain of Mus castaneus differed in binding of certain lectins at various sites, attesting to a genetic basis for individual variation. Hybrids between castaneus and domesticus mice also showed individual variation. Moreover, extensive differences between the mouse species were demonstrable with every lectin in glycoconjugates of stored secretions, Golgi cisternae, and apical or basolateral plasmalemma in many cell types. Totaling the differences in tabulated staining intensities for each possible species pair gave a measure of the overall extent of difference at 53 histological sites. According to this measure, the three species are about equally divergent from one another. Some differences between species appeared to depend on histological rather than histochemical variation, as, for example, a greater abundance of granular duct cells in the sublingual and submandibular glands in Mus hortulanus. Other differences were apparently derived from pathological change, as exemplified by casts and lymphoid infiltrates in kidney and structurally atypical submandibular gland lobules in Mus castaneus, and possibly by infiltrating cells in intestinal lamina propria and epithelium in Mus castaneus and hortulanus.     

Altered Turnover of Hypoxanthine Phosphoribosyltransferase in Erythroid Cells of Mice Expressing Hprt a and Hprt b Alleles

We have previously shown that mice expressing Hprt a allele(s) have erythrocyte hypoxanthine phosphoribosyltransferase (HPRT) levels that are approximately 25-fold (Mus musculus castaneus) and 70-fold (Mus spretus) higher than in mice that express the Hprt b allele (Mus musculus domesticus; C57BI/6J; C3H/HeHa), and that these differences in erythrocyte HPRT levels are due to differences in the turnover rates of the HPRT A and B proteins as reticulocytes mature to erythrocytes. We show here that: the taxonomic subgroups of the genus Mus are essentially monomorphic for the occurrence of either the Hprt a or the Hprt b allele, with Hprt a being common in the aboriginal species (M. spretus, Mus hortulanus and Mus abbotti) and in several commensal species (Mus musculus musculus, M. m. castaneus, Mus musculus molossinus), while Hprt b is common in feral M. m. domesticus populations as well as in all inbred strains of mice tested; in all these diverse Mus subgroups there is a strict association of Hprt a with high and Hprt b with low levels of erythrocyte HPRT; and, the association between the occurrence of the Hprt a allele and elevated erythrocyte HPRT levels is retained following repeated backcrosses of wild-derived Hprt a allele(s) into the genetic background of inbred strains of mice with the Hprt b allele. Collectively, these observations indicate that the elevated and low levels of erythrocyte HPRT are specified by differences in the Hprt a and b structural genes.(ABSTRACT TRUNCATED AT 250 WORDS)     

DNA insertions distinguish the duplicated renin genes of DBA/2 and M. hortulanus mice.

In a survey of inbred and wild mouse DNAs for genetic variation at the duplicate renin loci, Ren-1 and Ren-2, a variant Not I hybridization pattern was observed in the wild mouse M. hortulanus. To determine the basis for this variation, the structure of the M. hortulanus renin loci has been examined in detail and compared to that of the inbred strain DBA/2. Overall, the gross features of structure in this chromosomal region are conserved in both Mus species. In particular, the sequence at the recombination site between the linked Ren-1 and Ren-2 loci was found to be identical in both DBA/2 and M. hortulanus, indicating that the renin gene duplication occurred prior to the divergence of ancestors of these mice. Renin flanking sequences in M. hortulanus, however, were found to lack four DNA insertions totaling approximately 10.5 kb which reside near the DBA/2 loci. The postduplication evolution of the mouse renin genes is thus characterized by a number of insertion and/or deletion events within nearby flanking sequences. Analysis of renin expression showed little or no difference between these mice in steady state renin RNA levels in most tissues examined, suggesting that these insertions do not influence expression at those sites. A notable exception is the adrenal gland, in which DBA/2 and M. hortulanus mice exhibit different patterns of developmentally regulated renin expression.     

Y Chromosome Evolution in the Subgenus Mus (Genus Mus)

A 305 base pair DNA sequence isolated from the Y chromosome of the inbred mouse strain C57BL/10 was used to investigate the pattern and tempo of evolution of Y chromosome DNA sequences for five species in the subgenus Mus, including Mus spretus, Mus hortulanus, Mus abbotti, Mus musculus and Mus domesticus. Variation in hybridization patterns between species was characterized by differences in fragment lengths of both intensely and faintly hybridizing fragments, whereas variation in hybridization patterns within species was characterized primarily by differences in fragment lengths of faintly hybridizing fragments. Phylogenetic analyses were conducted based on fragment size variation within and among species. Phylogenetic relationships inferred from these analyses partly agree with the phylogenetic relationships obtained from biochemical and mitochondrial DNA data. We conclude that a set of DNA sequences common to the Y chromosomes of a closely related group of species in the subgenus Mus has evolved rapidly as reflected by sequence divergence and sequence amplification.     

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     

Low Diversity of T Haplotypes in the Eastern Form of the House Mouse, Mus Musculus L

In previous studies, 13 different recessive embryonic lethal genes have been associated with t haplotypes in the wild mice of the species Mus domesticus. In this communication we have analyzed five populations of Mus musculus for the presence and identity of t haplotypes. The populations occupy geographically distant regions in the Soviet Union: Altai Mountains, western and eastern Siberia, Azerbaijan and Turkmenistan. No t haplotypes were found in mice from eastern Siberia. In the remaining four populations, t haplotypes occurred with frequencies ranging from 0.07 to 0.21. All the t haplotypes extracted from these populations and analyzed by the genetic complementation test were shown to carry the same lethal gene tcl-w73. In one population (that of western Siberia), another lethal gene (tcl-w5) was found to be present on the same chromosome as tcl-w73. This situation is in striking contrast to that found in the populations of the western form of the house mouse, M. domesticus. In the latter species, tcl-w73 has not been found at all and the different populations are characterized by the presence of several different lethal genes. The low diversity of t haplotypes in M. musculus is consistent with lower genetic variability of other traits and indicates a different origin and speciation mode compared to M. domesticus. Serological typing for H-2 antigenic determinants suggests that most, if not all, of the newly described t haplotypes might have arisen by recombination of tw73 from M. musculus with t haplotypes from M. domesticus either in the hybrid zone between the two species or in regions where the two species mixed accidentally.     

Segregation of restriction fragment length polymorphism in an interspecies cross of laboratory and wild mice indicates tight linkage of the murine IFN-beta gene to the murine IFN-alpha genes.

Southern blot analysis with murine (Mu) interferon (IFN)-alpha cDNA of restricted genomic DNA of three inbred strains of mice belonging to the species Mus musculus domesticus (BALB/c, C57BL/6, and DBA/2) revealed only a limited degree of polymorphism. For example, with HindIII there were only two polymorphic bands out of 14 hybridizing fragments. With Mu IFN-beta cDNA there was no polymorphism at all between BALB/c and C57BL/6 in DNA restricted with seven different enzymes. In contrast, HindIII-restricted DNA of an inbred strain of wild mice (M. spretus Lataste) hybridized with the IFN-alpha probe displayed a high degree of polymorphism compared with the three strains of laboratory mice and was also polymorphic when probed with IFN-beta cDNA. Although M. musculus domesticus and M. spretus Lataste represent different species, certain interspecies crosses are possible in the laboratory. This enabled us to follow segregation of restriction fragment length polymorphism in HindIII-restricted DNA obtained from 18 backcross progeny of a (DBA/2 X M. spretus)F1 X DBA/2 interspecies cross. There was complete coincidence between the segregation of parental (DBA/2) and (DBA/2 X M. spretus)F1-type IFN-beta and IFN-alpha restriction fragment length polymorphism, indicating tight linkage of the IFN-beta and IFN-alpha genes. In addition, in 15 of 18 progeny the segregation coincided with that of the brown locus on chromosome 4, in accord with previous results obtained with the IFN-alpha probe in strains derived from crosses between BALB/c and C57BL/6 mice. Thus, the Mu IFN-beta gene is tightly linked to the Mu IFN-alpha gene cluster on chromosome 4 near the brown locus.     

DNA Sequence Analysis of Sry Alleles (Subgenus Mus) Implicates Misregulation as the Cause of C57bl/6j-Y(pos) Sex Reversal and Defines the Sry Functional Unit

The Sry (sex determining region, Y chromosome) open reading frame from mice representing four species of the genus Mus was sequenced in an effort to understand the conditional dysfunction of some M. domesticus Sry alleles when present on the C57BL/6J inbred strain genetic background and to delimit the functionally important protein regions. Twenty-two Sry alleles were sequenced, most from wild-derived Y chromosomes, including 11 M. domesticus alleles, seven M. musculus alleles and two alleles each from the related species M. spicilegus and M. spretus. We found that the HMG domain (high mobility group DNA binding domain) and the unique regions are well conserved, while the glutamine repeat cluster (GRC) region is quite variable. No correlation was found between the predicted protein isoforms and the ability of a Sry allele to allow differentiation of ovarian tissue when on the C57BL/6J genetic background, strongly suggesting that the cause of this sex reversal is not the Sry protein itself, but rather the regulation of SRY expression. Furthermore, our interspecies sequence analysis provides compelling evidence that the M. musculus and M. domesticus SRY functional domain is contained in the first 143 amino acids, which includes the HMG domain and adjacent unique region (UR-2).