Genetic regulation of estrogen-dependent repression of female-specific testosterone 16 alpha-hydroxylase (I-P-450(16 alpha) in male mouse liver: murine Ripr locus

The genetic basis for repression of I-P-450(16 alpha) in livers of male mice was examined in 129/J and BALB/cJ mice. Castration of adult male BALB/cJ but not 129/J mice resulted in derepression of I-P-450(16 alpha) at its mRNA and activity levels. It was further found that the patterns of derepression in (129/J x BALB/cJ) F1 and F2 offspring indicated that the derepression of I-P-450(16 alpha) is inherited as an autosomal additive trait. The distribution of derepression among castrated recombinant inbred strains (9 X A) indicated a close link of a locus repressing I-P-450(16 alpha) in male mice to the Rip locus on chromosome 7. Rip was previously defined as a locus that regulates specific expression of I-P-450(16 alpha) in livers of female mice [Noshiro, M., Lakso, M., Kawajiri, K., & Negishi, M. (1988) Biochemistry (preceding paper in this issue)]. Other tested inbred mice (A/HeJ, C57BL/6J, C3H/HeJ, and DBA/2J) showed the derepression of I-P-450(16 alpha) by castration, such as BALB/cJ. We propose Ripr (repression of an action of Rip locus in male mice) as the name of the locus by which repression of I-P-450(16 alpha) is regulated in male mice. Treatment of castrated male BALB/cJ mice by testosterone propionate, estradiol valerate, or diethylstilbestrol repressed I-P-450(16 alpha) to the levels seen in normal BALB/cJ male mice. Dihydrotestosterone, however, had little effect in repressing I-P-450(16 alpha) in castrated mice. The results suggested that estrogen rather than androgen is a repressor of I-P-450(16 alpha) in livers of male mice.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic basis of murine antibacterial defense to streptococcal lung infection

To evaluate the effect of genetic background on antibacterial defense to streptococcal infection, eight genetically diverse strains of mice (A/J, DBA/2J, CAST/Ei, FVB/NJ, BALB/cJ, C57BL/6J, 129/SvImJ, and C3H/HeJ) and tlr2-deficient mice (C57BL/6^tlr2−/−) were infected with three doses of Streptococcus zooepidemicus (500, 5,000, or 50,000 colony-forming units) by alveolar challenge. There was a range of susceptibility between the strains at each dose and time point (6, 24, and 96 h). At the lowest dose, the 129/SvImJ and C3H/HeJ strains had significantly higher bacterial counts at all time points after infection, when compared to A/J, DBA/2J, CAST/Ei, FVB/NJ, which were resistant to infection at the low dose of innoculum. At the medium dose, 129/SvImJ and C3H/HeJ had higher bacterial counts, while A/J, DBA/2J, and BALB/cJ showed reduced streptococcal growth. After the highest dose of Streptococcus, there were minimal differences between strains, suggesting the protective impact of modifier genes can be overcome. TLR2-deficient animals contained increased bacterial load with reduced cytokines after 96 h when compared to C57BL/6J controls suggesting a role of innate immunity in late antibacterial defense. Overall, we identify vulnerable (129/SvlmJ and C3H/HeJ) and resistant (A/J, FVB, and DBA) mouse strains to streptococcal lung infection, which demonstrate divergent genetic expression profiles. These results demonstrate that innate differences in pulmonary host defense to S. zooepidemicus are dependent on host genetic factors.     

Variation in Type 2 Diabetes-Related Phenotypes among Apolipoprotein E-Deficient Mouse Strains

We recently have found that apolipoprotein E-deficient (Apoe^-/-) mice with the C57BL/6 background develop type 2 diabetes when fed a Western diet for 12 weeks. In the present study we constructed multiple Apoe^-/- mouse strains to find diabetes-related phenotyptic variations that might be linked to atherosclerosis development. Evaluation of both early and advanced lesion formation in aortic root revealed that C57BL/6, SWR/J, and SM/J Apoe^-/- mice were susceptible to atherosclerosis and that C3H/HeJ and BALB/cJ Apoe^-/- mice were relatively resistant. On a chow diet, fasting plasma glucose varied among strains with C3H/HeJ having the highest (171.1 ± 9.7 mg/dl) and BALB/cJ the lowest level (104.0 ± 6.6 mg/dl). On a Western diet, fasting plasma glucose rose significantly in all strains, with C57BL/6, C3H/HeJ and SWR/J exceeding 250 mg/dl. BALB/cJ and C3H/HeJ were more tolerant to glucose loading than the other 3 strains. C57BL/6 was sensitive to insulin while other strains were not. Non-fasting blood glucose was significantly lower in C3H/HeJ and BALB/cJ than C57BL/6, SM/J, and SWR/J. Glucose loading induced the 1st and the 2nd phase of insulin secretion in BALB/cJ, but the 2nd phase was not observed in other strains. Morphological analysis showed that BALB/cJ had the largest islet area (1,421,493 ± 61,244 μm²) and C57BL/6 had the smallest one (747,635 ± 41,798 μm²). This study has demonstrated strain-specific variations in the metabolic and atherosclerotic phenotypes, thus laying the basis for future genetic characterization.     

Variations in the behaviors to novel objects among five inbred strains of mice

Novelty stimuli cause various behavioral responses, such as exploration and avoidance, and contextual variables may contribute to the behavioral outputs. Here, we tried to compare the behavioral responses to novel objects of five inbred strains of mice (C57BL/6J, 129/svJae, C3H/HeJ, BALB/cJ and DBA/2J) by using a modified novel object test where a small light-weight cube wrapped with paper was presented to mice in a home cage without beddings. In response to these objects, the C57BL/6J, 129/svJae and C3H/HeJ mice showed mild exploratory behaviors, such as approaching, sniffing or brief contact. In striking contrast, the BALB/cJ and DBA/2J mice, which have been known to show high avoidance/low exploration in other behavioral paradigms, exhibited play-like secondary reactions toward the objects after initial primary exploratory behaviors. Specifically, DBA/2J mice would move the object around in the cage, holding it with their mouths, and BALB/cJ mice would gnaw the object, eventually stripping off the wrapping paper. Such behaviors decreased when similar objects were presented repeatedly. The present results suggest that active manipulations of novel objects may be a relevant parameter for measuring novelty-induced behaviors in mice and appear to be strongly influenced by genetic factors.     

Taenia taeniaeformis: early inflammatory response around developing metacestodes in the liver of resistant and susceptible mice I. Identification of leukocyte response with monoclonal antibodies

Female BALB/cJ (resistant), C3H/HeJ (intermediate resistant), and C3H/HeDub (susceptible) inbred mice, 4-5 wk old, were infected with Taenia taeniaeformis. Liver sections were stained by an immunoperoxidase technique (avidin-biotin complex, ABC) for the differentiation antigens Lyt-1, Lyt-2, Mac-1, Mac-2, Mac-3, and B220. Binding of ABC to the cytoplasm of hepatocytes around the developing parasite was observed at 4 days postinfection (PI) in all 3 strains of mice, persisting in BALB/cJ and C3H/HeJ liver sections at 5 and 6 days PI, suggesting the presence of high concentrations of biotin, a fatty acid synthesis mediator. Two cell populations were labeled with B220 monoclonal antibodies: lymphocytes and polymorphonuclear (PMN) cells. At 4 days PI the number of labeled PMN cells peaked in infected C3H/HeJ and BALB/cJ mice; however a low number of PMN cells were labeled in infected C3H/HeDub mice. Few lymphocytes bound the B220 antibody in either BALB/cJ, C3H/HeJ, or C3H/HeDub infected mice. The number of Mac-1+ cells detected in infected C3H/HeJ and BALB/cJ liver sections were similar whereas fewer Mac-1+ cells were present in infected C3H/HeDub mice. Mac-2+ cells appeared in high numbers around the growing parasite at 5 and 6 days PI in the liver of C3H/HeDub mice, but not in the liver of BALB/cJ mice. Mac-3+ cells followed a similar pattern to that of the cell population defined by Mac-2. Few Lyt-1+ and Lyt-2+ cells were detected around the parasite site in the 3 strains of mice.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dominant low responsiveness in the IgG response of mice to the complex protein antigen type 1 fimbriae from Actinomyces viscosus T14V.

Type 1 fimbriae from Actinomyces viscosus T14V, composed of a complex protein of Mr 65,000, mediate the adherence of A. viscosus T14V to the host, whereas type 1 fimbriae-specific antibodies inhibit adherence. Genetic control of the serum IgG response to type 1 fimbriae was evaluated in a series of inbred, hybrid, recombinant inbred, and back-cross mice. Mice were given i.p. injections of 10(8) A. viscosus T14V cells in saline on days 0 and 14, and IgG anti-type 1 fimbriae in sera obtained on day 26 were measured by ELISA. Segregation analysis of the responses of (BALB/cJ x A/J)F1 x A/J backcross mice suggested polygenic control. Linkage analysis in (BALB/cJ x A/J)F1 x A/J backcross and SWXL recombinant inbred mice suggested control by genes linked with H-2 and with Ly-17 and Akp-1. In several F1 hybrid strains derived from H-2-disparate high and low responder parental strains, low responsiveness was dominant. The F1 derived from the H-2-identical high and low responder strains CBA/J and C3H/HeJ was a low responder, suggesting that dominant low responsiveness was mediated by non-H-2-linked genes. A three-gene model is proposed for regulation of the type 1 fimbriae response, including an MHC-linked gene, a gene linked with Ly-17 and Akp-1 on the telomeric portion of chromosome 1, and a background gene whose linkage is unknown.     

Genetic basis of murine responses to hyperoxia-induced lung injury

To evaluate the effect of genetic background on oxygen (O₂) toxicity, nine genetically diverse mouse strains (129/SvIm, A/J, BALB/cJ, BTBR+(T)/tf/tf, CAST/Ei, C3H/HeJ, C57BL/6J, DBA/2J, and FVB/NJ) were exposed to more than 99% O₂ for 72 h. Immediately following the hyperoxic challenge, the mouse strains demonstrated distinct pathophysiologic responses. The BALB/cJ and CAST/Ei strains, which were the only strains to demonstrate mortality from the hyperoxic challenges, were also the only strains to display significant neutrophil infiltration into their lower respiratory tract. In addition, the O₂-challenged BALB/cJ and CAST/Ei mice were among six strains (A/J, BALB/cJ, CAST/Ei, BTBR+(T)/tf/tf, DBA/2J, and C3H/HeJ) that had significantly increased interleukin 6 concentrations in the whole lung lavage fluid and were among all but one strain that had large increases in lung permeability compared with air-exposed controls. In contrast, the DBA/2J strain was the only strain not to have any significant alterations in lung permeability following hyperoxic challenge. The expression of the extracellular matrix proteins, including collagens I, III, and IV, fibronectin I, and tenascin C, also varied markedly among the mouse strains, as did the activities of total superoxide dismutase (SOD) and manganese-SOD (Mn-SOD or SOD2). These data suggest that the response to O₂ depends, in part, on the genetic background and that some of the strains analyzed can be used to identify specific loci and genes underlying the response to O₂.     

Tyrosine hydroxylase in various brain regions of three strains of mice differing in spontaneous activity, learning ability, and emotionality.

Tyrosine hydroxylase has been measured in brains of three inbred strains of mice ; DBA/2J ; C57 BL/6J and BALB/cJ. Compared to C57 BL/6J, DBA/2J showed a higher enzyme activity in hypothalamus, a lower activity in pons-medulla, and no significant changes in cortex or striatum. BALB/cJ showed a higher level of activity in all regions studied (striatum, pons-medulla and hypothalamus). No effect of isolation or of social dominance position were noted on the enzyme activities in C57 BL/6J or BALB/cJ mice.     

Interstrain variation in murine susceptibility to inhaled acid-coated particles

Epidemiologic studies have demonstrated a positive correlation between concentration of acid aerosol and increased morbidity and mortality in many urban environments. To determine whether genetic background is an important risk factor for susceptibility to the toxic effects of inhaled particles, we studied the interstrain (genetic) and intrastrain (environmental) variance of lung responses to acid-coated particle (ACP) aerosol in nine strains of inbred mice. A flow-past nose-only inhalation system was used to expose mice to ACPs produced by the cogeneration of a carbon black aerosol-sulfur dioxide (SO(2)) mixture at high humidity. Three days after a single 4-h exposure to ACPs or filtered air, mice underwent bronchoalveolar lavage, and cell differentials and total protein were determined as indexes of inflammation and epithelial permeability, respectively. To determine the effect of ACPs on alveolar macrophage (AM) function, lavaged AMs were isolated from exposed animals and Fc receptor-mediated phagocytosis was evaluated. Compared with air-exposed animals, there was a slight but significant exposure effect of ACPs on the mean number of lavageable polymorphonuclear leukocytes in C3H/HeJ and C3H/HeOuJ mice. ACP exposure also caused a significant decrease in AM phagocytosis. Relative to respective air-exposed animals, Fc receptor-mediated phagocytosis was suppressed in eight of nine strains. The order of strain-specific effect of ACPs on phagocytosis was C57BL/6J > 129/J > SJL/J > BALB/cJ > C3H/HeOuJ > A/J > SWR/J > AKR/J. There was no effect of ACP exposure on AM phagocytosis in C3H/HeJ mice. The significant interstrain variation in AM response to particle challenge indicates that genetic background has an important role in susceptibility. The effects of ACPs on AM function, inflammation, and epithelial hyperpermeability were not correlated (i.e., no cosegregation). This model may have important implications concerning interindividual variation in particle-induced compromise of host defense.     

Genetic analysis of strains C57BL/6J and BALB/cJ for Ath-1, a gene determining atherosclerosis susceptibility in mice

We previously reported that mice have at least one major gene determining atherosclerosis susceptibility, Ath-1. Susceptible alleles of Ath-1 are found in strain C57BL/6J and are associated with relatively low levels of high-density lipoprotein cholesterol (HDL-C) when these mice are fed an atherogenic diet. Resistant alleles of Ath-1 are found in strains C3H/HeJ and BALB/cJ and are associated with relatively high levels of HDL-C. Data reported earlier from the set of seven recombinant inbred (RI) strains, derived from C57BL/6By and BALB/cBy, showed that these parental strains differed at Ath-1. However, due to the limited number of RI strains, it was not possible to determine with certainty whether Ath-1 was the only major gene determining atherosclerosis susceptibility in these two strains or to determine its map position accurately. In this report, examination of F1, F2, and backcross progeny from a cross between C57BL/6J and BALB/cJ demonstrates that Ath-1 is the major gene determining atherosclerotic lesion formation and HDL-C levels in female mice. The data from male animals suggest that environmental factors or modifying genes also influence male HDL-C levels and thus partly obscure the Ath-1 phenotype. HDL-C levels in F1 progeny resemble the BALB/c parent. The data from the cross provide confirmatory evidence that Ath-1 is linked to Alp-2 on chromosome 1 with a map distance of 4.8 +/- 2.3 (SE). Combining these data with a previous cross between strain C57BL/6 and strain C3H/HeJ gives a map distance between Ath-1 and Alp-2 of 4.9 +/- 1.8 based on 7 crossovers found among 144 tested chromosomes.     

Translocation and amplification of an X-chromosome DNA repeat in inbred strains of mice.

A 9-kb repetitive DNA fragment (70-38) located near the centromere of the mouse X chromosome is amplified and translocated to an autosome in different inbred strains of mice. In situ hybridization and hybrid cell studies showed that probe 70-38 is located only on the X chromosome in mouse strains A/J, AKR/J, BALB/cJ, CBA/J, C3H/HeJ, C57BL/6J, DBA/2J and SWR/J. However, in four other mouse strains the DNA sequence is found near the centromere of an autosome in addition to the X chromosome. This autosome differs among the mouse strains (chromosome 11 in C57BL/10J or ScSn, chromosome 13 in NZB/B1NJ and chromosome 17 in SJL/J and PO). In those strains where the repeated sequence is located on an autosome, it has been amplified to about 100 copies. Restriction enzyme digestion patterns suggest a common structure for 70-38 sequences in the different strains. The changes in copy number, restriction enzyme digestion patterns, and chromosomal location of 70-38 reflect a rapid genomic evolution inbred mouse strains.     

Genetically determined differences in ethanol sensitivity influenced by body temperature during intoxication

The present study investigated the importance of body temperature during intoxication in mediating differences between five inbred strains of mice (C57BL/6J; BALB/cJ; DBA/2J; A/HeJ; 129/J) in their acute sensitivity to the hypnotic effects of ethanol. Mice exposed to 22 degrees C after ethanol injection became hypothermic and exhibited statistically significant differences between strains in rectal temperatures at the return of the righting reflex (RORR), duration of loss of the righting reflex (LORR), and blood and brain ethanol concentrations at RORR. Exposure to 34 degrees C after injection offset ethanol-hypothermia and markedly reduced strain-related differences in rectal temperatures and blood and brain ethanol concentrations at RORR. Brain ethanol concentrations at RORR were significantly lower in C57, BALB, DBA and A/He mice exposed to 34 degrees C compared to mice exposed to 22 degrees C during intoxication suggesting that offsetting hypothermia increased ethanol sensitivity in these strains. Taken with previous in vitro studies, these results suggest that genetically determined differences in acute sensitivity to the behavioral effects of ethanol reflect differences in body temperature during intoxication as well as differences in sensitivity to the initial actions of ethanol at the cellular level.     

Single gene control of resistance to cutaneous leishmaniasis in mice

A series of inbred, congenic resistant, and hybrid strains of mice were intradermally inoculated with 10⁶ promastigotes of Leishmania tropica. These mice were divided into susceptible and resistant groups using the criteria of lesion size, development of metastatic foci and skin-test reactivity. At 16 weeks of infection, resistant strains A/J, DBA/1J, AKR/J, CBA/J, C3H/HeJ, NZB/BINJ, C57BL/6J, C57BL/10Sn, B10.D2, B10.129(10M), and B10.CE(30NX) had completely resolved their lesions, while susceptible SWR/J and BALB/cJ mice demonstrated large, nonhealing cutaneous lesions. In addition, BALB/cJ developed metastatic lesions on the extremities which progressively increased in size. All BALB/cJ and SWR/J mice died by 7 1/2 months of infection. The BALB/cJ x C57BL/6JF₁ hybrid behaved in an intermediate fashion showing a slower expansion of cutaneous ulcers and a delayed development of metastatic foci, however, the infection ultimately proved fatal. The F₂ generation could be separated into three distinct groups: resistant, intermediate, and susceptible mice with a lesion size distribution pattern in conformity with a 1:2:1 ratio. Male/female susceptibility differences were not noted. These data indicated that development of acquired resistance may be under the control of a single, autosomal gene. The gene did not appear to be H-2-, Ir-2-, or H-11-linked as is seen with Leishmania donovani infections.     

Genetic control of chromosome synapsis in mice heterozygous for a paracentric inversion

Frequencies of formation of inversion loops and their relative sizes were studied in laboratory mice heterozygous at paracentric inversion In1(1)Rk in chromosome 1, depending on the genetic background. Homozygotes In1/In1 were crossed with mice from five inbred strains (A/HeJ, BALB/cJ, C3H/HeJ, C57BL/6J, DBA2/J). The frequency of formation of inversion loops, their relative sizes, and the dependence of these parameters on the stage of pachitene were analyzed on electron-microscopic slides of spread spermatocytes in first-generation hybrids. It was shown that the genetic background and cross direction statistically significantly influenced the duration of individual pachitene stages and the frequency of inversion loops, but not relative loop size. Using a database on SNP distribution in the inbred strains examined, we carried out in silico mapping of genes affecting the genotype-dependent characters. We have found that the efficiency of synapsis in the inversion does not depend on interstrain differences in homology of the chromosome 1 region involved in the inversion. Genes controlling the inversion loop frequency in the inversion heterozygotes were mapped to chromosome 7, and genes controlling the duration of individual pachitene stages, to chromosomes 2 and 5.     

Visual detection, pattern discrimination and visual acuity in 14 strains of mice

Based on the procedure of Prusky et al. (2000, Vision Research, 40, 2201-2209), we used a computer-based, two-alternative swim task to evaluate visual detection, pattern discrimination and visual acuity in 14 strains of mice from priority groups A and B of the JAX phenome project (129S1/SvImJ, A/J, AKR/J, BALB/cByJ, BALB/cJ, C3H/HeJ, C57BL/6J, CAST/Ei, DBA/2J, FVB/NJ, MOLF/Ei, SJL/J, SM/J and SPRET/Ei). Each mouse was tested for eight trials/day for 8 days on each of the three tests. There was a significant strain difference in visual ability in all three tests. Mice with reported normal vision (129S1/SvImJ, C57BL/6J and DBA/2J) and one albino strain (AKR/J) performed very well in these tasks. The other albino strains (A/J, BALB/cByJ and BALB/cJ) took longer to learn the tasks than mice with normal vision and did not reach the criterion of 70% correct. Mice with retinal degeneration (C3H/HeJ, FVB/NJ, MOLF/Ei and SJL/J) performed only at chance levels as did the three strains with unknown visual abilities (CAST/Ei, SM/J and SPRET/Ei). Because many behavioral tasks for rodents rely on visual cues, we suggest that the visual abilities of mice should be evaluated before they are tested in commonly used visuo-spatial learning and memory tasks.     

Optimal N-ethyl-N-nitrosourea (ENU) doses for inbred mouse strains

ENU is a powerful germline mutagen in the mouse, providing the opportunity to analyze the functions of large numbers of genes in the mammalian genome. In many mutagenesis experiments, it would be beneficial to exploit the advantages of inbred mouse strains. To perform an effective ENU mutagenesis screen using inbred mice, a dosage regimen is required to determine the optimal dose of ENU for that inbred strain, a time-consuming preliminary process. We have carried out dosage regimens for mutagenizing doses of ENU in ten inbred strains of mouse: 129X1/SvJ, 129S6/SvEv, A/J, BALB/cJ, BTBR/N, C3He/J, C3HeB/FeJ, C57BL/6J, C57BR/cdJ, and CBA/CaJ, and determined an optimal dose for each strain, defined by length of sterile period and number of males to survive treatment. Three strains: A/J, BALB/cJ and C57BL/6J, are able to tolerate high doses, up to 300 mg/kg body weight, and are highly recommended for mutagenesis studies.     

Female-predominant expression of testosterone 16 alpha-hydroxylase ("I"-P-450(16)alpha) and its repression in strain 129/J

Using specific testosterone 16 alpha-hydroxylase activity as the basis for selection of fractions during purification, the cytochrome P-450 ("I"-P-450(16)alpha) has been isolated from livers of phenobarbital-treated 129/J female mice [K. Devore, N. Harada, and M. Negishi (1985) Biochemistry, 24, 5632-5637]. An antibody elicited in rabbits to "I"-P-450(16)alpha was used to determine the amount of hepatic microsomal 16 alpha-hydroxylase activity due to "I"-P-450(16)alpha in untreated females and males of the two mouse strains, 129/J and BALB/cJ. The activities inhibited were 0.03 and 0.3 nmol/min/mg protein in the 129/J and BALB/cJ females, respectively. No significant level of "I"-P-450(16)alpha-dependent activity was detected in the microsomes from males of either mouse strain. Immunoblotting of microsomal proteins with the antibody to "I"-P-450(16)alpha revealed approximately a 10-fold greater amount of a 54-kDa protein in the microsomes from BALB/cJ than from 129/J females (0.03 and 0.26 pmol/micrograms protein, respectively). A cDNA clone (R17) for phenobarbital-inducible rat cytochrome P-450 selected "I"-P-450(16)alpha mRNA of mice, indicating a high degree of homology between the mRNAs of mouse "I"-P-450(16)alpha and phenobarbital-inducible rat cytochrome P-450s. Northern and dot hybridization of total mouse liver poly(A)+ RNA with the R17 cDNA probe indicated that the specific content of the hybridizable mRNA was more than 10 times higher in BALB/cJ females than in males, and that the mRNA level in female 129/J mice was very similar to that of 129/J and BALB/cJ males. The repression of "I"-P-450(16)alpha in 129/J females was inherited as an autosomal recessive trait in 129/J and BALB/cJ pairs as indicated by the levels of mRNA in female F1 offspring and the "I"-P-450(16)alpha-dependent hydroxylase activity. Female and male mice of eight more inbred strains (AKR/J, DBA/2J, C57BL/6J, C3H/HeJ, NZB/J, A/J, CBA/CaJ, and P/J) were tested for levels of mRNA. The results showed that the levels of mRNA were always 5- to 10-fold greater in the females than in the corresponding males, although there was some variation in the mRNA content in the males from the different strains. 129/J females appear to be a genetic variant where the female-predominant expression of the mRNA is repressed.     

Differential DNA-repair activity in prespermiogenic cells of various mouse strains

The present report demonstrates differential DNA-repair activity among 14 strains of immature (20 ± 2 days old) male mice (inbred strains: C57BL/6J, RF/J, Nude homo/nu, RIII/2J, Pl/J, AKR/J, Nude hetro/nude, C3H/HeJ, SWR/J, SM/J, ST/J, LP/J, BALB/cJ and random-bred strain: CD-1). The prespermiogenic cells were isolated and enriched by collagenase-trypsin digestion of seminiferous tubules and subsequent 3% albumin-gradient centrifugation. Enriched prespermiogenic cells demonstrated a viabiilty greater than 95% by trypan blue exclusion criteria. For in vitro unscheduled DNA synthesis (UDS) determination, prespermiogenic cells (10⁶ cells/ml) were incubated with methyl methanesulfonate (0.4 mM) in the presence of 20 mM hydroxyurea (HU). At 20 mM HU concentration, 90% of S-phase DNA activity in prespermiogenic cells was inhibited and thus, the net UDS activity following MMS exposure was readily determined. MMS-induced UDS activity in the CD-1 mouse strain was both linear up to 4 h of incubation and dose-dependent at 4 h incubation. The apparent K_m for MMS-induced UDS activity in prespermiogenic cells was approx. 1.8 × 10^?4 M. Of the 14 mice strains tested, C57BL/6J and RF/J exhibited the highest DNA-repair activity, while BALB/cJ, LP/J, and ST/J showed the lowest. A maximal difference in UDS activity fo 3.5-fold was observed between C57BL/6J and BALB/cJ. Furthermore, a 2.5-fold difference was also noted between RF/J and LP/J mouse strains. Thus, wide variations in DNA-repair activity among 14 mouse strans were clearly demonstrated. Whether genetically select mouse strains with the lowest DNA-repair activity should have greater sensitivity toward environmental mutagens needs to be tested.     

Genetic dissection of intermale aggressive behavior in BALB/cJ and A/J mice

Aggressive behaviors are disabling, treatment refractory, and sometimes lethal symptoms of several neuropsychiatric disorders. However, currently available treatments for patients are inadequate, and the underlying genetics and neurobiology of aggression is only beginning to be elucidated. Inbred mouse strains are useful for identifying genomic regions, and ultimately the relevant gene variants (alleles) in these regions, that affect mammalian aggressive behaviors, which, in turn, may help to identify neurobiological pathways that mediate aggression. The BALB/cJ inbred mouse strain exhibits relatively high levels of intermale aggressive behaviors and shows multiple brain and behavioral phenotypes relevant to neuropsychiatric syndromes associated with aggression. The A/J strain shows very low levels of aggression. We hypothesized that a cross between BALB/cJ and A/J inbred strains would reveal genomic loci that influence the tendency to initiate intermale aggressive behavior. To identify such loci, we conducted a genomewide scan in an F2 population of 660 male mice bred from BALB/cJ and A/J inbred mouse strains. Three significant loci on chromosomes 5, 10 and 15 that influence aggression were identified. The chromosome 5 and 15 loci are completely novel, and the chromosome 10 locus overlaps an aggression locus mapped in our previous study that used NZB/B1NJ and A/J as progenitor strains. Haplotype analysis of BALB/cJ, NZB/B1NJ and A/J strains showed three positional candidate genes in the chromosome 10 locus. Future studies involving fine genetic mapping of these loci as well as additional candidate gene analysis may lead to an improved biological understanding of mammalian aggressive behaviors.