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PubMed1995

The molecular mechanism underlying the "rare allele phenomenon" in a subspecific hybrid zone of the California field mouse, Peromyscus californicus.

Natural hybrid zones are known to have unusually high levels of novel or otherwise rare electrophoretic variants (the "rare allele phenomenon"). These variant alleles are most likely the result either of high levels of unique mutations in hybrids or of intragenic recombination between divergent alleles from the parental populations. This study uses DNA sequence comparisons to determine which process has produced a rare allele of the 6-phosphogluconate dehydrogenase (6-PGD) gene in a subspecific hybrid zone of the California field mouse (Peromyscus californicus). About 70% of the coding sequence of 6-PGD was cloned and sequenced from three alleles, including two widespread alleles and one rare allele unique to hybrid populations. Sequence comparisons among the three alleles reveal no patterns that would indicate that the variant was formed by intragenic recombination. Instead, the unique allele of 6-PGD studied seems to have developed by the accumulation of base substitutions, which supports the hypothesis of increased mutation rates in hybrids.

Alleles↗

PubMed1996

Reproductive and immune responses to photoperiod and melatonin are linked in Peromyscus subspecies.

The effects of photoperiod and melatonin treatment on reproductive and immune function were assessed in two subspecies of Peromyscus maniculatus from different latitudes of origin. In experiment 1, P. m. bairidii (latitude = 42 degrees 51' N) and P. m. luteus (latitude = 30 degrees 37' N) were housed in either long (LD 16:8) or short days (LD 8:16) for 8 weeks. Short-day P. m. bairdii displayed reproductive regression and elevated splenocyte proliferation in response to the T-cell mitogen concanavalin A, as compared to long-day mice. In contrast, P. m. luteus did not undergo reproductive regression or exhibit any increase in lymphocyte proliferation in short days. In experiment 2, individuals of both P. m. bairdii and P. m. luteus were implanted with empty capsules or capsules that contained melatonin. Individual P. m. bairdii implanted with melatonin underwent reproductive regression. Individuals of this subspecies also displayed elevated lymphocyte proliferation compared to control mice. Conversely, P. m. luteus implanted with melatonin did not undergo reproductive regression and displayed no significant changes in lymphocyte proliferation. These results suggest that reproductive responsiveness to melatonin mediates short-day enhancement of immune function in deer mice. These data also imply that melatonin may not possess universal immunoenhancing properties. Rather, the effectiveness of melatonin to influence immune responses may be constrained by reproductive responsiveness to this indole-amine.

Animals↗

PubMed1983

On the occurrence of a myeloid body in pinealocytes of the white-footed mouse, Peromyscus leucopus. An electron-microscopic study.

The fine-structural features of pinealocytes of the white-footed mouse, Peromyscus leucopus, were examined. A single population of pinealocytes was observed in both superficial and deep components of the gland. Cells in both locations are characterized by the presence of an indented nucleus exhibiting a prominent nucleolus. The usual organelles in the perikaryon are the Golgi complexes, mitochondria, endoplasmic reticulum, polysomes, microtubules and dense-core vesicles. In addition the perikaryonal cytoplasm often contains a single myeloid body. These bodies are usually lenticular in shape, are formed of an array of flattened membranous cisternae, and are not bounded by a limiting membrane. This organelle usually lies in the vicinity of the nucleus and is infrequently associated with lipid bodies. Complex forms were also observed. The cisternae are continuous with elements of the endoplasmic reticulum at points along their expanded rims. The outer surface of the cisternal membrane exhibits a granularity or fuzziness. The cisternae may be fenestrated. Pinealocyte processes with an abundance of clear vesicles, and some dense-core vesicles and vesicle-crowned rodlets are present in the parenchyma.

Animals↗

PubMed1994

Characteristics of a white-footed mouse (Peromyscus leucopus) population inhabiting a polychlorinated biphenyls contaminated site.

Demographic characteristics of a white-footed mouse (Peromyscus leucopus) population inhabiting a woodland containing a low level of PCBs contamination were compared to an uncontaminated reference site. Although population density was higher on the PCBs-contaminated grid, the population exhibited greater temporal variability among years and had a higher number of transient animals. These population trends are consistent with those observed in structurally suboptimal habitats, indicating that the PCBs-contaminated grid is functioning as a suboptimal habitat. However, the data are not compelling enough to firmly conclude that the differences are due to contamination rather than to undetected environmental variation between sites. If demographic differences due to contamination are slight, they will be difficult to detect against a background of demographic variation resulting from subtle environmental differences. We conclude that animals at this site experienced a level of contamination that was below threshold for unequivocal detection of demographic effects.

Animals↗

PubMed1982

Preantral intra-ovarian oocyte release in the white-footed mouse, Peromyscus leucopus.

Adult white-footed mice, Peromyscus leucopus, were kept either in long photoperiod (LP; LD 16:8) or in short photoperiod (SP; LD 8:16) for six weeks. Ovaries were serially sectioned and examined histologically. Preantral follicles were observed to release their oocyte into the ovarian stroma. This phenomenon is termed "preantral intra-ovarian oocyte release (PIOR)". The first step in PIOR appeared to be the interruption of the basal membrane and the thecal layer. PIOR was considered incomplete when the oocyte was retained in the follicular compartment. PIOR was complete when granulosa cells were seen to be herniated and the oocyte released either into the interstitial cortical tissue or into a corpus luteum. During incomplete PIOR signs of atresia were increased, whereas during complete PIOR they were decreased. Resumption of meiosis was not seen. PIOR was observed in 19.5% of the ovaries after LP and in 18.8% of the ovaries after SP. PIOR is regarded as a sign of follicular atresia.

Animals↗

PubMed1990

Major histocompatibility complex class I genes of Peromyscus leucopus.

Class I genes of the Peromyscus leucopus major histocompatibility complex (MhcPele) were examined by Southern blot hybridization, genomic cloning, and DNA sequencing. At least three distinct subtypes of Pele class I genes were discerned, which we have designated Pele-A, B, and C. The nucleotide sequences of exon 5-containing regions (encoding the transmembrane domain) suggested that Pele-A genes are homologs of mouse H-2K, D, L, and Q genes and that Pele-B genes correspond to mouse Tla genes. The Pele-C genes appeared similar to mouse M1 genes. The number of unique genes in each subtype cloned from an individual P. leucopus were 20 for Pele-A, 13 for Pele-B, and 2 for Pele-C. Three genomic clones showed cross-hybridization to both Pele-A and Pele-B gene-specific probes. Six genomic clones remained unclassified as they did not cross-hybridize to exon 5-containing probes from Pele-A, B, or C genes. The homology between the transmembrane domains of Pele class I gene subtypes was found to be similar to that observed between the transmembrane domains of H-2 subtypes (or groups). Interspecific similarity of exon 5 was found to be 81%-88% between Pele class I genes and their H-2 counterparts.

Animals↗

PubMed1991

The effect of unsaturated and saturated dietary lipids on the pattern of daily torpor and the fatty acid composition of tissues and membranes of the deer mouse Peromyscus maniculatus.

Dietary lipids strongly influence the pattern of torpor and the body lipid composition of mammalian hibernators. The object of the present study was to investigate whether these diet-induced physiological and biochemical changes also occur in species that show shallow, daily torpor. Deer mice, Peromyscus maniculatus, were fed with rodent chow (control diet) or rodent chow with either 10% sunflower seed oil (unsaturated diet) or 10% sheep fat (saturated diet). Animals on the unsaturated diet showed a greater occurrence of torpor (80-100% vs 26-43%), longer torpor bouts (4.5 vs 2.25 h), a lower metabolic rate during torpor (0.96 vs 2.25 ml O2.g-1.h-1), and a smaller loss of body mass during withdrawal of food (2.35 vs 3.90 g) than animals on the saturated diet; controls were intermediate. These diet-induced physiological changes were associated with significant alterations in the fatty acid composition of depot fat, leg muscle and brain total lipids, and heart mitochondrial phospholipids. Significant differences in the total unsaturated fatty acid (UFA) content between animals on saturated and unsaturated diet were observed in depot fat (55.7% vs 81.1%) and leg muscle (56.4% vs 72.1%). Major compositional differences between diet groups also occurred in the concentration of n6 and/or n3 fatty acids of brain and heart mitochondria. The study suggests that dietary lipids may play an important role in the seasonal adjustment of physiology in heterothermic mammals.

Adipose Tissue↗

PubMed1980

Analysis of a BrdU-sensitive site in the cactus mouse (Peromyscus eremicus): chromosomal breakage and sister-chromatid exchange.

When the thymidine analog BrdU was incorporated into the DNA of a fibroblast cell line derived from the cactus mouse Peromyscus eremicus, a chromosome region with an increased frequency of gaps and breaks was observed. Nearly a third of the chromatid aberrations found at this site were associated with a sister-chromatid exchange (SCE) although this chromosome region showed no increase in sister-chromatid exchange in the absence of a gap or break. SCEs were significantly decreased in the remainder of the chromosome arm when it contained an aberration at the unstable site. This BrdU-sensitive region, unlike others reported, was found not to be late-replicating.--In this chromosome complement, the frequency of sister-chromatid exchange in C-band positive regions was significantly lower than that in C-band negative regions.

Animals↗

PubMed1986

The behavior and morphology of the X and Y chromosomes during prophase I in the Sitka deer mouse (Peromyscus sitkensis).

Surface-spread, silver-stained primary spermatocytes from individuals of the Sitka deer mouse (Peromyscus sitkensis) were analyzed by electron microscopy. Pairing of the X and Y chromosomes is initiated at early pachynema and is complete by mid pachynema. The pattern of sex chromosome pairing is unique in that it is initiated at an interstitial position, with subsequent synapsis proceeding in a unidirectional fashion towards the telomeres of the homologous segments. One-third the length of the X and two-thirds the length of the Y are involved in the synaptonemal complex of the sex bivalent. Various morphological complexities develop in the heteropycnotic (unpaired) segments as pachynema progresses, but desynapsis is not initiated until diplonema. Analysis of C-banded diakinetic nuclei indicated that sex chromosome pairing involves the heterochromatic short arm of the X and the long arm of the heterochromatic Y. An interstitial chiasma between the X and Y was observed in the majority of the diakinetic nuclei. The observation of a substantial pairing region and chiasma formation between the sex chromosomes of these deer mice is interpreted as indicating homology between the short arm of the X and the long arm of the Y.

Animals↗

PubMed1993

Genome organization of repetitive elements in the rodent, Peromyscus leucopus.

To document the frequency and distribution of repetitive elements in Peromyscus leucopus, the white-footed mouse, a cosmid genomic library was examined. Two thousand thirteen randomly chosen recombinants, with an average insert size of 35 kb and representing 2.35% of the haploid genome of P. leucopus, were screened with probes representing microsatellites, tandem repeats, and transposable elements. Of the four dinucleotides, (GT)n was present in 87% of the clones, (CT)n was present in 59% of the clones, and (AT)n and (GC)n each was represented in our sample by a single clone (0.05%). (TCC)n was present in 8% of the clones. Of the tandem repeats, the 28S ribosomal probe and the (TTAGGG)n telomere probe were not represented in the library, whereas a heterochromatic fragment was present in 9% of the clones. A transposable element, mys, was estimated to occur in 4700 copies, whereas a long interspersed element (LINE) was estimated to occur in about 41,000 copies per haploid genome. LINE and mys occurred together in the same clones more frequently than expected on the basis of chance. Hybridizing the library to genomic DNA from P. leucopus, Reithrodontomys fulvescens, Mus musculus, and human produced general agreement between phylogenetic relatedness and intensity of hybridization. However, dinucleotide repeats appeared to account for a disproportionately high number of positive clones in the more distantly related taxa.

Animals↗

PubMed1978

Genetic regulation of liver alcohol dehydrogenase in Peromyscus.

Data from genetic crosses of Peromyscus maniculatus and P. polionotus suggests that electrophoretic variants of liver alcohol dehydrogenase are coded by alleles at a single locus. These alleles, designated AdhF, AdhS, and AdhN, determine, respectively, the fast, slow, and not detectable (null) ADH electrophoretic phenotype. Heterozygotes (AdhF/AdhS) exhibit three bands on zymograms, suggesting a dimeric subunit structure for the enzyme. However, AdhF/AdhN and AdhS/AdhN animals exhibit a single band, suggesting that the AdhN allele does not produce a polypeptide subunit capable of dimerizing into an active molecule. Fast and slow electrophoretic phenotypes exhibit multiple bands which can be converted into single major fast and slow bands, respectively, upon treatment with oxidized or reduced NAD. Addition of NAD also stabilizes both the fast and slow enzyme to heat inactivation at 60 C for at least 30 min.

Alcohol Oxidoreductases↗

PubMed1990

Intracellular pH during daily torpor in Peromyscus maniculatus.

Intracellular and extracellular acid-base parameters during normothermy and daily torpor were examined in deer mice (Peromyscus maniculatus). [14C]Dimethyloxazolidinedione and [3H]inulin were used to assess intracellular pH in liver, heart, skeletal muscle, and brain. Buffering capacities were determined using tissue homogenates. A significant increase in plasma PCO2 and CCO2 during daily torpor indicates a respiratory acidosis. All tissues experienced a reduction in the calculated dissociation ratio of histidine imidazole groups (alpha imid) during daily torpor (16.5% for brain, approximately 10% for other tissues). Based on comparisons with physicochemical tissue buffering capacities, metabolic compensation of the respiratory acidosis occurred in liver, heart, and plasma, while brain was more acidotic than predicted. The more extensive change in brain alpha imid might influence a regulated decrease in body temperature. Comparison of acid-base parameters during daily torpor and hibernation suggests that the magnitude of acid-base modifications in mammals may be associated with the level of dormancy.

Acid-Base Equilibrium↗

PubMed1985

Effects of ambient temperature and altitude on ventilation and gas exchange in deer mice (Peromyscus maniculatus).

The effects of different ambient temperatures (Ta) on gas exchange and ventilation in deer mice (Peromyscus maniculatus) were determined after acclimation to low and high altitude (340 and 3,800 m). At both low and high altitude, oxygen consumption (VO2) decreased with increasing Ta at Ta from -10 to 30 degrees C. The VO2 was 15-20% smaller at high altitude than at low altitude at Ta below 30 degrees C. Increased VO2 at Ta below thermoneutrality was supported by increased minute volume (VI) at both low and high altitude. At most Ta, the change in VI was primarily a function of changing respiration frequency (f); relatively little change occurred in tidal volume (VT) or oxygen extraction efficiency (O2EE). At Ta = 0 degree C and below at high altitude, VI was constant due to declining VT and O2EE increased in order to maintain high VO2. At high altitude, VI (BTP) was 30-40% higher at a given Ta than at low altitude, except at Ta below 10 degrees C. The increased VI at high altitude was due primarily to a proportional increase in f, which attained mean values of 450-500 breaths/min at Ta below 0 degree C. The VI (STP) was equivalent at high and low altitude at Ta of 10 degrees C and above. At lower Ta, VI (STPD) was larger at low altitude. At both altitudes, respiratory heat loss was a small fraction (less than 10%) of metabolic heat production, except at high Ta (20-30 degrees C).

Acclimatization↗

PubMedDate not supplied

An ecotoxicological study of a population of the white footed mouse (Peromyscus leucopus) inhabiting a polychlorinated biphenyls-contaminated area.

White footed mice (Peromyscus leucopus) inhabiting an area surrounding a pond (Tyler) contaminated with polychlorinated biphenyls (PCBs) and metals (Cadmium, Zinc, Copper) had whole body burdens of 0.42-4.17 ppm PCBs (mean 2.3 ppm) and animals from a comparison nonpolluted site (WCC) had no detectable PCBs. Males and females caught at the polluted site in the winter months were not significantly different in body weight or length when compared to WCC animals, but Tyler animals had significantly increased relative liver, kidney, spleen and adrenal weights. In the summer months, mostly males were caught at both Tyler and WCC sites. Tyler males were significantly lighter than WCC males, and had a significantly increased relative liver weight when compared to the males from the WCC site. In addition, the adult Tyler males had significantly lower relative testis weights. At Tyler there was a significantly smaller proportion of juveniles and subadults in the population than at WCC. Polychlorinated biphenyls levels in the adult Tyler males were significantly positively correlated with relative liver weight, but there were no significant correlations with any of the other structures measured. These results suggest that at the polluted site there is inhibition of reproduction and changes in liver, spleen, adrenal, and testis function.

Animals↗

PubMed1983

Ultrastructure of the pineal gland of the brush mouse (Peromyscus boylei): influence of long and short photoperiod.

The ultrastructure of the pineal gland of wild-captured brush mice (Peromyscus boylei) was examined. A homogeneous population of pinealocytes was present in the pineal gland of this species. The Golgi apparatus, granular endoplasmic reticulum, mitochondria, lysosomes, dense-core vesicles, vacuoles containing fluocculent material, clear vesicles, microtubules and glycogen particles were consistent components of the pinealocyte cytoplasm; infrequently-observed organelles included centrioles, "synaptic" ribbons, subsurface cisternae, multivesicular bodies, lipid droplets and annulate lamellae-like structures. Quantitative comparison of pinealocyte ultrastructure revealed larger cross-sectional areas of cytoplasma, nucleus, Golgi apparatus, granular endoplasmic reticulum, mitochondria and vacuoles containing flocculent material as well as higher number of dense-core vesicles in the animals kept in short photoperiod (LD 8 : 16) as compared to those in animals kept in long photoperiod (LD 16 : 8). These observations suggest that restricting the amount of light to which animals are exposed activated the pinealocytes of brush mice.

Animals↗

PubMed1994

Comparison of chromosomal distribution of a retroposon (LINE) and a retrovirus-like element mys in Peromyscus maniculatus and P. leucopus.

Chromosomal distribution for two interspersed elements (LINEs and mys) that are thought to have established their chromosomal position primarily by transposition was compared between two species of deer mice (Peromyscus leucopus and P. maniculatus). Both LINEs and mys generally produced an autosomal banding pattern reflective of G-bands and both hybridized preferentially to the sex chromosomes. The pattern on the long arm of the X was unique for each, with mys reflecting the G-bands (four bands with the telomeric most prominent) and LINE producing five equally spaced bands of equal intensity. LINE also preferentially hybridized to the short arm of the longest autosomal pair. Some aspects of these patterns are explained adequately with proposed mechanisms that would produce a non-random pattern of chromosomal distribution (i.e. both reflect autosomal G-bands and both preferentially insert into AT-rich regions characteristic of G-bands). However, other aspects such as the differences observed on the long arm of the X do not appear to fit any predictions of proposed mechanisms.

Animals↗

PubMed1996

Genetic and phylogenetic analyses of hantaviral sequences amplified from archival tissues of deer mice (Peromyscus maniculatus nubiterrae) captured in the eastern United States.

The S and M segments of a hantavirus, enzymatically amplified from tissues of Cloudland deer mice (Peromyscus maniculatus nubiterrae) captured during 1985 in West Virginia, diverged from strains of Four Corners virus from the southwestern United States by more than 16% and 6% at the nucleotide and amino acid levels, respectively. Phylogenetic analysis suggested that this virus strain (designated Monongahela) forms a possible evolutionary link between the Four Corners and New York hantaviruses.

Amino Acid Sequence↗

PubMed1990

Unequal crossing over and heterochromatin exchange in the X-Y bivalents of the deer mouse, Peromyscus beatae.

Differences in length of the heterochromatic short arms of the X and Y chromosomes in individuals of Peromyscus beatae are hypothesized to result from unequal crossing over. To test this hypothesis, we examined patterns of synapsis, chiasma formation, and segregation for male P. beatae which were either heterozygous or homozygous for the amount of short-arm sex heterochromatin. Synaptonemal complex analysis demonstrated that mitotic differences in heterochromatic short-arm lengths between the X and Y chromosomes were reflected in early pachynema as corresponding differences in axial element lengths within the pairing region of the sex bivalent. These length differences were subsequently eliminated by synaptic adjustment such that by late pachynema, the synaptonemal complex configurations of the XY bivalent of heterozygotes were not differentiable from those of homozygotes. Crossing over between the heterochromatic short arms of the XY bivalent was documented by the routine appearance of a single chiasma in this region during diakinesis/metaphase I. Sex heterochromatin heterozygotes were characterized by the presence of asymmetrical chiasma between the X and Y short arms at diakinesis/metaphase I and sex chromosomes with unequal chromatid lengths at metaphase II. These data corroborate our hypothesis on the role of unequal crossing over in the production and propagation of X and Y heterochromatin variation and suggest that, in some cases, crossing over can occur during the process of synaptic adjustment.

Animals↗