Dichlorvos toxicity in the white-footed mouse (Peromyscus leucopus)

The organophosphate pesticide, dichlorvos (DDVP), is used commonly to control ectoparasites in laboratory rodents colonies. This compound is relatively nontoxic to Mus musculus at dosages several times the therapeutic level. However, usage of a similar therapeutic level in the white-footed mouse (Peromyscus leucopus) resulted in substantial mortality. To determine whether P. leucopus is more susceptible than M. musculus to the toxic effects of DDVP, both species were exposed to 0, 3 and 6 g of pelleted DDVP per cage. In a subsequent experiment, P. leucopus were exposed to 0 and 1 g of DDVP per cage. Mortality was not observed in M. musculus at any dosage level. P. leucopus exposed to 1, 3 and 6 g of DDVP exhibited mortalities of 3%, 20% and 53%, respectively. Mean serum cholinesterase in P. leucopus exposed to 3 and 6 g of DDVP was 0.35 and 0.21 U/ml as compared to 3.13 U/ml in unexposed mice. The analogous values for M. musculus were 1.60 and 0.79 U/ml while the level in unexposed mice was 6.79 U/ml. In the second experiment, mean serum cholinesterase in P. leucopus exposed to 1 g of DDVP was 0.32 U/ml as compared to 2.33 U/ml in unexposed mice. Histopathology revealed no lesions in the brain, liver or kidneys. The increased susceptibility of P. leucopus to the toxic effects of DDVP was related to the lowered serum cholinesterase. This indicates that DDVP should not be used for control of ectoparasites in P. leucopus.     

Diverse wild mouse origins of xenotropic, mink cell focus-forming, and two types of ecotropic proviral genes

We analyzed wild mouse DNAs for the number and type of proviral genes related to the env sequences of various murine leukemia viruses (MuLVs). Only Mus species closely related to laboratory mice carried these retroviral sequences, and the different subclasses of viral env genes tended to be restricted to specific taxonomic groups. Only Mus musculus molossinus carried proviral genes which cross-reacted with the inbred mouse ecotropic MuLV env gene. The ecotropic viral env sequence associated with the Fv-4 resistance gene was found in the Asian mice M. musculus molossinus and Mus musculus castaneus and in California mice from Lake Casitas (LC). Both M. musculus castaneus and LC mice carried many additional Fv-4 env-related proviruses, two of which are common to both mouse populations, which suggests that these mice share a recent common ancestry. Xenotropic and mink cell focus-forming (MCF) virus env sequences were more widely dispersed in wild mice than the ecotropic viral env genes, which suggests that nonecotropic MuLVs were integrated into the Mus germ line at an earlier date. Xenotropic MuLVs represented the major component of MuLV env-reactive genes in Asian and eastern European mice classified as M. musculus molossinus, M. musculus castaneus, and Mus musculus musculus, whereas Mus musculus domesticus from western Europe, the Mediterranean, and North America contained almost exclusively MCF virus env copies. M. musculus musculus mice from central Europe trapped near the M. musculus domesticus/M. musculus musculus hybrid zone carried multiple copies of both types of env genes. LC mice also carried both xenotropic and MCF viral env genes, which is consistent with the above conclusion that they represent natural hybrids of M. musculus domesticus and M. musculus castaneus.     

Genetics of intracisternal-A-particle-related envelope-encoding proviral elements in mice.

Intracisternal-A-particle-related envelope-encoding (IAPE) proviral elements in the mouse genome encode and express an envelope-like protein that may allow transmission of IAPEs as infectious agents. To test IAPE mobility and potential transmission in mice, we have analyzed the distribution of IAPE elements in the genomes of Mus spretus and Mus musculus inbred strains and wild-caught animals. Potential full-length (IAPE-A) proviral elements are present as repetitive copies in DNA from male but not female animals of M. musculus inbred strains and Mus musculus castaneus. Analysis of IAPE-cellular junction fragments indicates that fixation of most IAPEs in the germ line occurred in M. musculus and M. spretus after speciation but before M. musculus inbred strains were derived.     

Structural analysis of type II variants within the mouse intracisternal A-particle sequence family.

Intracisternal A-particle (IAP) elements are present in multiple copies in the mouse and other rodent genomes. The bulk of this sequence family in Mus musculus consists of 7 Kb long elements, but the majority of IAP sequences involved in known transpositions have been deleted forms. The present study describes a subset of deleted IAP sequences (type II IAP) characterized by insertion of a particular short sequence element (AIIins). AIIins are interspersed and the majority occur as part of the type II IAP elements in the mouse genome. AIIins sequences are absent or in low copy number outside Mus musculus. We have isolated clones containing AIIins from a mouse genomic DNA library and have sequenced three isolates of AIIins and their surrounding IAP sequences to define the detailed structure of type II elements. AIIins are 272, 268 and 264 bp long and 90% homologous in sequence. They are bracketed by 9 bp duplications, suggesting they may be inserted elements. A 75 bp region containing a core enhancer sequence is repeated at the 5' end in type II IAP elements. Insertion into the IAP genome, with potential to encode an integrase function, may have played a role in the amplification of AIIins.     

Life shortening in mice exposed to fission neutrons and gamma rays. VI. Studies with the white-footed mouse, Peromyscus leucopus

Some of the studies on late effects of neutron and gamma radiation previously carried out with the C57BL6 X BALB/c F1 hybrids of Mus musculus have been repeated with the white-footed mouse, Peromyscus leucopus, a cricetid rodent of a different subfamily, with differing physiological characteristics and a different spectrum of pathologies. Among the more important findings were the following: For both species, the life shortening per rad at low doses of either radiation was the same percentage of the life span. The limiting values of the relative biological effectiveness for life shortening from all causes of death were about the same for the two species, ranging from 8 to 16, depending on the method of calculation. Fractionated neutron exposures failed to produce significant life shortening in Peromyscus over that observed at single doses. Tumor-related deaths accounted for at least 70 to 75% of the radiation-specific excess mortality in Peromyscus.     

Genomic 5-methyldeoxycytidine decreases with age

Significant losses of DNA 5-methyldeoxycytidine residues in old age could disrupt cellular gene expression and contribute to the physiological decline of the animal. Thus, the 5-methyldeoxycytidine content of DNAs, isolated from the tissues of two rodent species of various ages, were determined. Mus musculus lost DNA methylation sites at a rate of about 4.7 X 10(4) (approximately 0.012% of the newborn level)/month. Peromyscus leucopus lost DNA 5-methyldeoxycytidine residues at a rate of only 2.3 X 10(4) (approximately 0.006% of the newborn level)/month. Since P. leucopus generally live twice as long as M. musculus, the rate of loss of DNA 5-methyldeoxycytidine residues appears to be inversely related to life span. Similar losses in genomic 5-methyldeoxycytidine content were also observed to correlate with donor age in cultured normal human bronchial epithelial cells.     

Vascular superoxide and hydrogen peroxide production and oxidative stress resistance in two closely related rodent species with disparate longevity

Vascular aging is characterized by increased oxidative stress, impaired nitric oxide (NO) bioavailability and enhanced apoptotic cell death. The oxidative stress hypothesis of aging predicts that vascular cells of long-lived species exhibit lower production of reactive oxygen species (ROS) and/or superior resistance to oxidative stress. We tested this hypothesis using two taxonomically related rodents, the white-footed mouse (Peromyscus leucopus) and the house mouse (Mus musculus), that show a more than twofold difference in maximum lifespan potential (MLSP = 8 and 3.5 years, respectively). We compared interspecies differences in endothelial superoxide (O2-) and hydrogen peroxide (H2O2) production, NAD(P)H oxidase activity, mitochondrial ROS generation, expression of pro- and antioxidant enzymes, NO production, and resistance to oxidative stress-induced apoptosis. In aortas of P. leucopus, NAD(P)H oxidase expression and activity, endothelial and H2O2 production, and ROS generation by mitochondria were less than in mouse vessels. In P. leucopus, there was a more abundant expression of catalase, glutathione peroxidase 1 and hemeoxygenase-1, whereas expression of Cu/Zn-SOD and Mn-SOD was similar in both species. NO production and endothelial nitric oxide synthase expression was greater in P. leucopus. In mouse aortas, treatment with oxidized low-density lipoprotein (oxLDL) elicited substantial oxidative stress, endothelial dysfunction and endothelial apoptosis (assessed by TUNEL assay, DNA fragmentation and caspase 3 activity assays). According to our prediction, vessels of P. leucopus were more resistant to the proapoptotic effects of oxidative stressors (oxLDL and H2O2). Primary fibroblasts from P. leucopus also exhibited less H2O2-induced DNA damage (comet assay) than mouse cells. Thus, increased lifespan potential in P. leucopus is associated with a decreased cellular ROS generation and increased oxidative stress resistance, which accords with the prediction of the oxidative stress hypothesis of aging.     

Peromyscus maniculatus--Mus musculus chromosome homology map derived from reciprocal cross species chromosome painting

The Mus musculus and Rattus norvegicus genomes have been extensively studied, yet despite the emergence of Peromyscus maniculatus as an NIH model for genome sequencing and biomedical research much remains unknown about the genome organization of Peromyscines. Contrary to their phylogenetic relationship, the genomes of Rattus and Peromyscus appear more similar at the gross karyotypic level than either does to Mus. We set out to define the chromosome homologies between Peromyscus, Mus and Rattus. Reciprocal cross-species chromosome painting and G-band homology assignments were used to delineate the conserved chromosome homology map between P. maniculatus and M. musculus. These data show that each species has undergone extensive chromosome rearrangements since they last shared a common ancestor 25 million years ago (mya). This analysis coupled with an inferred homology map with Rattus revealed a high level of chromosome conservation between Rattus and Peromyscus and indicated that the chromosomes of Mus are highly derived.     

Molecular evolution of two lineages of L1 (LINE-1) retrotransposons in the california mouse,Peromyscus californicus.

The large number of L1 [long interspersed elements (LINE)-1] sequences found in the genome is due to the insertion of copies of the retrotransposon over evolutionary time. The majority of copies appear to be replicates of a few active, or "master" templates. A continual replacement of master templates over time gives rise to lineages distinguishable by their own unique set of shared-sequence variants. A previous analysis of L1 sequences in deer mice, Peromyscus maniculatus and P. leucopus, revealed two active L1 lineages, marked by different rates of evolution, whose most recent common ancestor predates the expansion of the Peromyscus species. Here we exploit lineage-specific, shared-sequence variants to reveal a paucity of Lineage 2 sequences in at least one species, P. californicus. The dearth of Lineage 2 copies in P. californicus suggests that Lineage 2 may have been unproductive until after the most recent common ancestor of P. californicus and P. maniculatus. We also show that Lineage 1 appears to have a higher rate of evolution in P. maniculatus relative to either P. californicus or P. leucopus. As a phylogenetic tool, L1 lineage-specific variants support a close affinity between P. californicus and P. eremicus relative to the other species examined.     

Molecular cloning and long terminal repeat sequences of intracisternal A-particle genes in Mus caroli

We isolated DNA clones of intracisternal A-particle (IAP) genes from the genome of an Asian wild mouse, Mus caroli. A typical M. caroli IAP gene was 6.5 kilobase pairs in length and had long terminal repeat (LTR) sequences at both ends. The size of the LTR was 345 base pairs in clone L20, and two LTRs at both ends of this clone were linked to directly repeating cellular sequences of 6 base pairs. Each LTR possessed most of the structural features commonly associated with the retrovirus LTR. The restriction map of the M. caroli IAP gene resembled that of Mus musculus, although the M. caroli IAP gene was 0.4 kilobase pairs shorter than the M. musculus IAP gene in two regions. Sequence homology between the M. caroli and M. musculus IAP LTRs was calculated as about 80%, whereas the LTR sequence of the Syrian hamster IAP gene was about 60% homologous to the M. caroli LTR. The reiteration frequency of the M. caroli IAP genes was estimated as 200 to 400 copies per haploid genome, which is at least 10 times the reported value. These results suggest that the IAP genes observed in the genus Mus are present in multiple copies with structures closely resembling the integrated retrovirus gene.     

Alterations in liver mitochondrial function as a result of fasting and exhaustive exercise

Two-dimensional displays of the restriction fragments from the DNA of Mus musculus revealed a complex species-specific pattern produced from nonsatellite repetitive sequences. The patterns have been used as a guide in the direct purification of a group of broadly interspersed repeated DNA sequences (characterized by a 1350-bp Eco-Bam fragment) that have been studied by molecular cloning, restriction mapping and genomic Southern blotting. These studies show that the cloned representatives originate from an abundant group of sequences that share homology with about 2% of the mouse genome. The sequences do not appear to share homology with mouse-interspersed-family-1 (MIF-1) nor with the major AT-rich satellite sequences of mouse. They appear to be part of a group of larger repetitive elements that is both broadly interspersed and heavily methylated in normal mouse tissue.     

Diverse long terminal repeats are associated with murine retroviruslike (VL30) elements.

The VL30 family is a retroviruslike gene family with no apparent nucleic acid homology to any known retrovirus. Over 100 copies of VL30 DNA elements are dispersed throughout the mouse genome. Sequence analysis of the VL30 long terminal repeat (LTR) units showed that, whereas the LTR units of a given VL30 DNA element were almost identical, the LTR units associated with distinct members of the family were very different from one another. Comparison of the LTR sequences possessed by two particular VL30 DNA elements revealed a pattern of extensively homologous DNA segments adjacent to only distantly related DNA sequences. With the aid of sub-LTR probes, it was shown that a certain LTR is composed of both U5 sequences that are abundantly present in all species of the genus Mus and a U3 region detected only in Mus musculus. In addition, we isolated a VL30 DNA element in which the LTR units were replaced by the LTR units of an apparently novel retroviruslike family. These findings suggest that recombinations have played a role in generating the diverse population of VL30-associated LTRs.     

Molecular cloning of retrovirus-like genes present in multiple copies in the Syrian hamster genome.

Endogenous retrovirus-like sequences homologous to intracisternal type-A particle (IAP) genes, which are present in the inbred mouse (Mus musculus) genome, were cloned from a Syrian hamster gene library. A typical hamster IAP gene was 7 kb long and segments homologous to long terminal repeat (IAP) sequences present in Mus musculus IAP genes were located at both ends of the gene. Contrary to the pattern found in the Mus musculus IAP genes, the organization of the cloned hamster IAP genes was not markedly polymorphic and deletion was not observed among these cloned genes. A sequence about 0.8 kb long and located close to the 3' end of the hamster IAP gene was well conserved in both IAP gene families, although they showed less overall homology with one another. The reiteration frequency of the hamster IAP genes was calculated to be 950 copies per haploid genome. Since such IAP genes with the above properties were not found in the genome of the Chinese hamster, whose progenitors diverged from those of the Syrian hamster about 7.5 Myr ago, the integration of a huge number of Syrian hamster IAP genes must have occurred subsequent to such divergence.     

An evolutionary switch in tissue-specific gene expression. Abundant expression of alpha 1-antitrypsin in the kidney of a wild mouse species

alpha 1-Antitrypsin (AT), one of the major proteinase inhibitors in mammalian serum, is generally considered to be synthesized exclusively in the liver. We have found that a wild-derived Mus species, Mus caroli, expresses AT mRNA in kidney at levels approaching that in liver; no other mouse, inbred or wild-derived, exhibits this striking property. Liver and kidney mRNAs from M. caroli encode very similar AT polypeptides that are distinct from that encoded by Mus musculus liver mRNA. In vivo, liver AT is secreted into the bloodstream, while kidney AT, which is processed differently from the liver protein, is excreted into the urine. Analysis of RNA from a hybrid between M. musculus and M. caroli indicates that a cis-acting genetic element may be responsible for the difference in AT expression. Restriction enzyme digestion patterns of AT genomic sequences in M. caroli DNA are considerably different from those in M. musculus; in addition, these sequences are undermethylated in liver DNA from M. musculus and in liver and kidney DNA from M. caroli, reflecting the respective patterns of expression. Further studies of the altered tissue specificity of AT expression that is apparent in these two related species should lead to new insights into the nature and evolution of genetic determinants of tissue-specific phenotypes.     

Diversity of mammary tumor viral genes within the genus Mus, the species Mus musculus, and the strain C3H.

Proviral sequences complementary to the C3H mouse mammary tumor virus RNA genome are present in the DNA of early occurring mammary tumors of C3H/HeN mice and are absent from apparently normal C3H/HeN tissues; these sequences are non-germ line transmitted in C3H/HeN mice and have been termed tumor-associated sequences; (W. Drohan et al., J. Virol. 21:986-995, 1977). We report here that tumor-associated sequences are present in the DNA of spontaneous mammary tumors that occur early in the life of several inbred, high-tumor-incidence mouse strains but are absent in mammary tumors that occur later in life in low- and moderate-tumor-incidence strains. These sequences are also absent in apparently normal organs tested from numerous laboratory mouse strains, feral mice, Mus musculus subspecies, and other Mus species. Sequences represented in tumor-associated sequence RNA, however, are present as endogenous provirus in GR mice (at approximately four copies per haploid genome) and in two of five substrains of C3H mice tested (at approximately one copy per haploid genome). The two substrains of C3H mice positive for endogenous tumor-associated sequence provirus were recently (circa 1930) separated from the negative substrains of C3H mice. The results may be explained by the unlikely chance segregation of proviral sequences or by the recent integration of viral genes (within the last few decades). Whereas radioactively labeled mouse mammary tumor virus 60-70S RNA or complementary DNA detected mouse mammary tumor virus-related proviral information in all laboratory mouse strains, feral mice, subspecies of M. musculus, and other species of Mus, the use of tumor-associated sequence RNA clearly revealed the genetic diversity that may exist between different colonies or substrains of "inbred" laboratory mice commonly used in cancer research.     

Terminally redundant sequences in cellular intracisternal A-particle genes.

The sequences coding for intracisternal A-particle RNA form a family of related but not identical genetic elements which are present in 650 to 1,000 copies within the mouse genome. We showed that different intracisternal A-particle genes had a terminally redundant sequence of about 400 base pairs, one-half of which arose from the 3' end of the intracisternal A-particle RNA. A second portion of the redundant region did not contain 3-related sequences and was probably derived from the 5' end of intracisternal A-particle RNA. Thus, there were endogenous intracisternal A-particle genes in the cellular DNA-3'-5'--3'-5'-cellular DNA configuration identified for type B and C retroviruses. This indicated that the initial integration of intracisternal A-particle genes into the Mus musculus genome occurred by the same mechanism as the integration of other retroviruses. Two types of heterogeneity were identified among the 5' sequences of the two genes.     

Isolation and Characterization of a Mouse Y Chromosomal Repetitive Sequence

The Y chromosome plays a dominant role in mammalian sex determination, and characterization of this chromosome is essential to understand the mechanism responsible for testicular differentiation. Male mouse genomic DNA fragments, cloned into pBR322, were screened for the presence of Bkm (a female snake satellite DNA)-related sequences, and we obtained a clone (AC11) having a DNA fragment from the mouse Y chromosome. In addition to a Bkm-related sequence, this fragment contained a Y chromosomal repetitive sequence. DNA isolated from the XX sex-reversed male genome produced a hybridization pattern indistinguishable to that obtained with normal female DNA, suggesting that the AC11 sequence is not contained within the Y chromosomal DNA present in the sex-reversed male genome. Based on the hybridization patterns against mouse Y chromosomal DNA, AC11 classified 16 inbred laboratory strains into two categories; those with the Mus musculus musculus type Y chromosome and those with the M.m. domesticus type Y chromosome. Three European subspecies of Mus musculus (M.m. brevirostris, M.m. poschiavinus and M.m. praetextus) possessed the M.m. domesticus type Y chromosome, whereas the Japanese mouse, M.m. molossinus, had the M.m. musculus type Y chromosome. The survey was also extended to six other species that belong to the genus Mus, of which M. spretus and M. hortulamus showed significant amounts of AC11-related sequences in their Y chromosomes. The male-specific accumulation of AC11-related sequences was not found in M. caroli, M. cookii, M. pahari or M. platythrix. This marked difference among Mus species indicates that the amplification of AC11-related sequences in the mouse Y chromosome was a recent evolutionary event.