Inbred Strains Of Male Mice Research Articles

Variation in Genome-Wide Levels of Meiotic Recombination Is Established at the Onset of Prophase in Mammalian Males

Segregation of chromosomes during the first meiotic division relies on crossovers established during prophase. Although crossovers are strictly regulated so that at least one occurs per chromosome, individual variation in crossover levels is not uncommon. In an analysis of different inbred strains of male mice, we identified among-strain variation in the number of foci for the crossover-associated protein MLH1. We report studies of strains with “low” (CAST/EiJ), “medium” (C3H/HeJ), and “high” (C57BL/6J) genome-wide MLH1 values to define factors responsible for this variation. We utilized immunofluorescence to analyze the number and distribution of proteins that function at different stages in the recombination pathway: RAD51 and DMC1, strand invasion proteins acting shortly after double-strand break (DSB) formation, MSH4, part of the complex stabilizing double Holliday junctions, and the Bloom helicase BLM, thought to have anti-crossover activity. For each protein, we identified strain-specific differences that mirrored the results for MLH1; i.e., CAST/EiJ mice had the lowest values, C3H/HeJ mice intermediate values, and C57BL/6J mice the highest values. This indicates that differences in the numbers of DSBs (as identified by RAD51 and DMC1) are translated into differences in the number of crossovers, suggesting that variation in crossover levels is established by the time of DSB formation. However, DSBs per se are unlikely to be the primary determinant, since allelic variation for the DSB-inducing locus Spo11 resulted in differences in the numbers of DSBs but not the number of MLH1 foci. Instead, chromatin conformation appears to be a more important contributor, since analysis of synaptonemal complex length and DNA loop size also identified consistent strain-specific differences; i.e., crossover frequency increased with synaptonemal complex length and was inversely related to chromatin loop size. This indicates a relationship between recombination and chromatin compaction that may develop as DSBs form or earlier during establishment of the meiotic axis.

Genetic variation in the structural pattern of osteoclast activity during post-natal growth of mouse femora

While the spatial activity of osteoblasts has been associated with modeling of bones during development, few studies have examined if variation in the spatial activity of osteoclasts also contributes to the morphogenesis of skeletal tissues. We examined this question by histomorphometric analysis and reconstructing the three-dimensional spatial distribution of osteoclasts in the femora of three inbred strains of male mice (A/J, C57BL/6J [B6], and C3H/HeJ [C3H]) that have differing skeletal, structural, and material properties. Our data show that total osteoclast surface area and osteoclast numbers are related to the overall bone density, but not related to the development of bone diameter or overall cortical area. The analysis of the spatial distribution of the osteoclasts showed that the asymmetrical mid-diaphyseal distribution of osteoclasts in A/J and B6 compared to the more uniform distribution of these cells around the circumference in the C3H mice was consistent with the more ellipsoid shape of A/J and B6 femora compared to the more circular mid-diaphyseal shape of the femora in the C3H mice. The statistically 2- to 3-fold fewer cells on the periosteal surface in the C3H compared to either the B6 or A/J mice is also consistent with the greater cortical thickness that is seen for the C3H mice compared to either B6 or A/J strains. In vitro studies of osteoclastogenesis and the expression of numerous phenotypic properties of osteoclasts prepared from the three strains of mice showed that A/J and B6 mice developed statistically greater numbers of tartrate resistant acid phosphatase (TRAP) positive cells and expressed statistically higher levels of multiple mRNAs that are unique to differentiated osteoclasts than those isolated from the C3H strain. In summary, the 3D reconstructions and histomorphometric analysis suggest that genetic differences lead to spatial variation in the distribution of osteoclasts. These variations in spatial distribution of osteoclasts in turn contribute in part to the development of the structural variations of the femora that are seen in the three strains of mice. In vitro studies suggest that intrinsic genetic variation in osteoclastogenesis and their phenotypic expression may contribute to the differences in their functional activities that give rise to the unique spatial distributions of these cells in bones.

Parent-of-origin effects on cardiac response to pressure overload in mice

Left ventricular (LV) hypertrophy (LVH) is an independent risk factor for cardiovascular mortality and is commonly caused by hypertension. In rodents, transverse aortic constriction (TAC) is a model regularly employed in mechanistic studies of the response of the LV to pressure overload. We previously reported that inbred strains of male mice manifest different cardiac responses to TAC, with C57BL/6J (B6) developing LV dilatation and impaired contractility and 129S1/SvImJ (129) males displaying concentric LVH. In the present study, we investigated sex and parent-of-origin effects on the response to TAC by comparing cardiac function, organ weights, expression of cardiac hypertrophy markers, and histology in female B6 and female 129 mice and in F1 progeny of reciprocal crosses between B6 and 129 mice (B6129F1 and 129B6F1). Five weeks after TAC, heart weight increased to the greatest extent in 129B6F1 mice and the least extent in 129 and B6129F1 mice. Female 129B6F1 and B6 mice were relatively protected from the increase in heart weight that occurs in their male counterparts with pressure overload. The response to TAC in 129 consomic mice bearing the B6 Y chromosome resembled that of 129 rather than 129B6F1 mice, indicating that the B6 Y chromosome does not account for the differences in the reciprocal cross. Our results suggest that susceptibility to LVH is more complex than simple Mendelian inheritance and that parental origin effects strongly impact the LV response to TAC in these commonly used inbred strains.

Genetic analysis of intestinal cholesterol absorption in inbred mice

A genetic mapping strategy was employed to identify chromosomal regions harboring genes that influence the absorption of intestinal cholesterol in the mouse. Analysis of seven inbred strains of male mice (129P3, AKR, BALB/c, C3H/He, C57BL/6, DBA/2, and SJL, all from Jackson Laboratories) revealed substantial differences in their abilities to absorb a bolus of cholesterol delivered by gavage. Crosses between high (AKR, 129) and low (DBA/2, SJL) absorbing strains revealed evidence for the presence of dominant genes that increase and decrease cholesterol absorption. Backcrosses between F1 offspring and parental strains (DBA/2xAKD2F1 and 129xSJL129F1) followed by linkage analyses revealed four quantitative trait loci that influenced cholesterol absorption. Analyses of recombinant inbred strains identified an additional three loci affecting this phenotype. These seven quantitative trait loci, which map to different chromosomes and are termed Cholesterol absorption 1–7 (Chab1–7) loci, together influence the absorption of intestinal cholesterol in mice and are likely to be involved in different steps of this complex pathway.—Schwarz, M., D. L Davis, B. R. Vick, and D. W. Russell. Genetic analysis of intestinal cholesterol absorption in inbred mice.

The absence of impairment of cliff avoidance reaction induced by subchronic methamphetamine treatment in inbred strains of mice.

Cliff avoidance reaction (CAR), an index of behavioral teratology in rodents, can be impaired by motor, arousal, or cognitive dysfunction. We formerly reported subchronic administration of methamphetamine (MAP) induced the CAR impairment, which might reflect MAP-induced cognitive dysfunction, in three strains of rats. In this study, the effects of subchronic MAP treatment on the behavioral sensitization in stereotypy (stereotypy sensitization) and CAR were examined in two inbred strains of male mice; C57BL/6J(C57) and DBA/2J(DBA). The animals received 4 mg/kg/day MAP intraperitoneally for 28 days. There were apparent strain differences in the development of stereotypy sensitization induced by chronic MAP; DBA mice developed stereotypy sensitization quickly, but C57 did not. Unlike rats, neither strains of mice showed the CAR impairment. These results suggest that chronic MAP (4 mg/kg) administration did not introduce any cognitive dysfunction measured by CAR in the two inbred mice, DBA and C57. The discrepancy between rats and mice is still unclear. It might relate to the species-selective effect of MAP on the CAR impairment. Further studies should to be required.

Effects of Testosterone and 7α-Methyl-19-Nortestosterone (MENT) on Sexual and Aggressive Behaviors in Two Inbred Strains of Male Mice

Behavioral and endocrine effects of a synthetic androgen, 7α-methyl-19-nortestosterone (MENT), which is not 5α-reduced to dihydrotestosterone, were compared to those of testosterone in two inbred strains of male mice, C57BL/6J and DBA/2J, in two experiments. In the first experiment, seminal vesicle (SV) weights, kidney weights, and circulating steroid levels were examined in castrated mice treated with three doses of testosterone (3.125, 12.5, or 50 μg/day) or four doses of MENT (1, 4, 16, or 64 μg/day) for 2 weeks to determine the optimal replacement levels of the two androgens for behavioral studies. Both testosterone and MENT dose-dependently increased the SV weights that were greatly reduced, in both strains, by castration. MENT was more effective than testosterone in increasing SV weights, fully restoring them to intact levels in both strains, at the dose of 4 μg/day. At the dose of 12.5 μg/day, testosterone restored the SV weights completely in C57BL/6J and up to 80% in DBA/2J mice. DBA/2J mice were more sensitive than C57BL/6J mice to both androgens, as measured by kidney weights, although circulating levels of either steroid were very similar between the two strains of mice. In the second experiment, we investigated the effects of testosterone (12.5 μg/day) and MENT (4 μg/day) on sexual and aggressive behaviors. In each strain, MENT-treated and testosterone-treated mice showed similar numbers of mounts or intromissions. MENT was equally effective as testosterone to fully (C57BL/6J) or partially (DBA/2J) restore sexual behaviors as well as the SV weights to the intact levels. In contrast, MENT-treated mice of both strains were much less aggressive than testosterone-treated mice. In both C57BL/6J and DBA/2J mice, testosterone fully restored aggression to the intact levels as measured by aggression latency, number of aggressive bouts, and duration of aggression, whereas aggressive behaviors of the MENT-treated groups were not different from those of the castrated control groups. These results suggest that MENT can restore both male sexual behaviors and reproductive organ weights as effectively as testosterone, at one-third of the testosterone dose, without stimulating male aggressive behaviors.

Genetic differences in the locomotor response to single and daily doses of phencyclidine in inbred mouse strains.

Genetic differences in the locomotor stimulant effects of both single and daily administration of phencyclidine were investigated in four inbred strains of male mice A/J, C57BL/6J, C57BL/6ByJ and BALB/cByJ. Each mouse was injected i.p. once in Experiment 1, or daily for 5 or 11 days in Experiments 2, 3 and 4. Locomotor activity was assessed with an automated photoelectric system. Significant strain differences were found in the response to a single as well as repeated doses of phencyclidine. A/J mice showed the greatest initial response to phencyclidine and developed tolerance to daily phencyclidine. C57BL/6ByJ mice showed initial resistance to acute phencyclidine, but developed sensitization to daily phencyclidine. The responses of both C57BL/6J and BALB/cByJ mice to acute phencyclidine were low to moderate, and did not change significantly following daily phencyclidine. The results of this study indicate that different genetic mechanisms are involved in responses to single and daily injections of phencyclidine.

The identification of Y chromosome-linked markers with random sequence oligonucleotide primers.

The polymerase chain reaction (PCR)-based technique of random amplification of polymorphic DNA (RAPD) is extremely useful for developing DNA-based markers. We previously identified a linkage group of eight unmapped RAPD markers that distinguish C57BL/6J and DBA/2J mice (Mammalian Genome 3: Woodward et al., 73-78, 1992). In this study, we report that all eight markers are Y Chromosome (Chr)-linked. One additional Y-linked RAPD was discovered serendipitously during the screening of a C3H/HeJ x (C3H/HeJ x SJL/J)F1 BC1 population. The segregation of all nine markers was analyzed with a panel of 14 independent inbred strains of male mice. The nine markers could be divided into three distinct groups: (1) DYByu2, DYByu5, DYByu6, and DYByu8 identify both the M.m. musculus and M.m. domesticus type Y Chr; (2) DYByu1, DYByu3, DYByu4, and DYByu7 are specific for the M.m. musculus type; and (3) DYByu9 is specific for the M.m. domesticus type. The results clearly indicate that the RAPD technique can be used to identify Y Chr-linked, DNA-based markers in mammalian species.

The cerium-induced liver injury and oxidative frug metabolism in DBA/2 and C57BL/6 mice

The influence of the known hepatotoxic agent, cerium (Ce) on the activity of liver microsomal monoxygenases, especially coumarin 7-hydroxylase (COH) was investigated in two inbred strains of male mice, DBA/2N and C57BL/6N. Ce wqas injected ibtravenously in three doses (0.5, 1.0 and 2.0 mg/kg body wt) and the animals were killed 24 or 72 gh alter. On the basis of histological assessment of the liver , C57BL/6N mice are apparently more resistant to the hepatotoxic effect of Ce. At 24 h COH activity was increased in a dose-dependent manner in DBA/2 animals, whereas no change was seen in C57BL/6N animals. A significantly increase in all other enzymes studied, cytochrome P−450 (P450), ethoxycoumarin O-deethylase and ehtoxyresorufin O-deethylase, was seen in DBA/2 mice injected with the highest dose of Ce. At 72 h Ce increased CON activity, as well as other enzymes, in C57Bl/6N mice in a dose-dependent manner, whereas in DBA/2 mice the increase was only seen after two lower doses, the highest dose causing severe morphological changes in the liver structure and a clear decrease in COH and other activities. The distribution studies with Ce-141 showed that C57BL/6N livers contained more Ce than DBA/2 livers after the highest dose.

Characteristics of Wheel-Running Activity in Nine Inbred Strains of Male Mice under 12L-12D Cycle

Characteristics of Wheel-Running Activity in Nine Inbred Strains of Male Mice under 12L-12D Cycle

Running-wheel avoidance learning in mice (Mus musculus): Evidence of contingency learning and differences among inbred strains.

In experiment 1, male ICR mice learned active- and passive-avoidance responses in the running wheel situation with active- and passive-avoidance contingencies and were compared with yoked and nonshocked control animals (ns per group=7). Avoidance performance of the experimental mice differed from that of the control mice, which shows that the experimental mice learned the two types of avoidance responses. In Experiment 2, male ICR mice (n=6) learned a multiple active-passive (MAP) avoidance behavior. In experiment 3, the MAP procedure was used to assess the differences among 4 inbred strains of male mice (DBA/2J, BALB/cBy, C3H/HeJ, and C57BL/6J ; ns per strain=8)

Pharmacogenetic study of the effect of morphine on the plasma cyclic AMP and cyclic GMP level and on motor activity in five inbred strains of mice

We examined the difference in the effects of morphine on the plasma cyclic AMP and cyclic GMP level as well as motor activity in 5 inbred strains of male mice. Thirty min after morphine (40 mg/kg, s.c), plasma cyclic AMP level increased in C57BL, C3H and A/J mice,but not in BALB and DBA strain. Morphine increased plasma cyclic GMP level in C57BL, C3H, BALB and A/J and marginally in DBA strain mice. Motor activity determined between 25 and 30 min after the administration of morphine increased in the 3 strains of mice except A/J (no change) and DBA (decrease). These results indicate a clear strain difference in the effects of morphine with contrasting changes in C57BL and DBA strains. F1 hybrids between C57BL and DBA showed an intermediate response to morphine with no change in plasma cyclic AMP and motor activity and a slight increase in plasma cyclic GMP. The backcross populations (F1 x C57BL, F1 x DBA) again showed intermediate responses between F1 and each parent in the 3 parameters determined. These findings suggest that the effects of morphine on plasma cyclic AMP, cyclic GMP and motor activity in the 2 strains of mice are determined, at least in part, genetically; however,no dominance was observed between C57BL and DBA when changes in plasma cyclic nucleotides and motor activity are considered.

Strain difference in morphine-induced increase in plasma cyclic AMP and cyclic GMP levels in relation to locomotor activity in male mice.

The effects of morphine on plasma cyclic nucleotide levels and on locomotor activity were investigated in four inbred strains of male mice. Morphine increased both cyclic AMP and cyclic GMP levels as well as locomotor activity in C57BL/6N mice. In BALB/cAnN mice, morphine increased plasma cyclic GMP levels and motor activity without changes in plasma cyclic AMP levels. In C3H/HeN mice, morphine increased plasma cyclic GMP levels without changing cyclic AMP levels and motor activity, but neither plasma cyclic nucleotide levels nor motor activity were increased by morphine in DBA/2N mice. Epinephrine and carbachol increased plasma cyclic AMP and cyclic GMP levels, respectively, in both C57BL and DBA mice. These results show that there is a significant strain difference in the effects of morphine on plasma cyclic nucleotide levels as well as motor activity. The major cause of strain difference in the effects of morphine on cyclic nucleotide levels is unlikely to be due to the difference in the regulation of adenylate cyclase linked to adrenoceptors or that of guanylate cyclase connected with cholinoceptors.

Lithium chloride toxicity and pharmacodynamics in inbred mice.

Inbred strains of male mice (C3H, DBA, BALB, C57) were used to determine whether genetic factors play a role in lithium toxicity. Significant differences in the LD50 for LiCl were observed between the mouse strains after a subcutaneous injection of 37 degrees isotonic LiCl. The LD50 values in the C3H, DBA, BALB and C57 strains were 17.4, 17.6, 18.2, and 19.4 mmol/kg, respectively. Significant differences were also observed between the mouse strains in the concentrations of lithium in plasma, heart, liver, kidney and brain 2 hrs. after a subcutaneous injection of 15.1 or 18.2 mmol/kg LiCl, but the lithium concentrations were not related in an obvious manner to LiCl toxicity. The results show that genetic factors can influence the toxicity and pharmacodynamics of lithium.

Virus-Induced Diabetes Mellitus. III. Influence of the Sex and Strain of the Host

Nineteen inbred strains of male mice were infected with encephalomyocarditis virus. Five strains became hyperglycemic and had abnormal values in glucose tolerance tests; three strains remained normoglycemic but had abnormal values in glucose tolerance tests; and the remaining strains showed no abnormalities in blood glucose levels or glucose tolerance tests. Female mice from three of five strains tested also developed hyperglycemia, but in one strain (DBA/2) the hyperglycemia was less severe in females than in males. Castrated DBA/2 males developed less severe hyperglycemia than uncastrated males, even though the degree of damage to beta cells appeared to be similar in the two groups. Host factors apparently influence both the development and expression of virus-induced diabetes mellitus.

Atrophic changes and adrenal cortical lipids

The adrenal glands from four inbred strains of male mice were investigated with reference to age-associated degenerative changes, and the effect of such changes on the distribution and density of the adrenal lipids as revealed by sections stained with Sudan black. An average of approximately 0.17 of the cortex in 35 per cent of the specimens was affected in varying by degenerative changes. The sudanophil material in the necrotic areas was abnormal in appearance, and occurred in subnormal and variable amounts in inverse proportion to the degree of cellular degeneration. The cortical areas which showed advanced stages of cellular degeneration contained little or no sudanophil material. The tabulated data indicate the incidence of cellular degeneration in the adrenal glands from mice of different strains and two age groups.