Relationship between genetic differentiation of the thymus in mice of different strains and malignant growth. IV. Genetic analysis of the thymic index in mice]

Relative thymus weight was estimated in C3H/He, C57BL/6 mice, their F1 and backcross hybrids, as well as in the progeny of complete diallel crosses between the BALB/c, C3H/He, C57BL/6 and AKR/J strains. On the basis of the analysis of these measurements, a conclusion is drawn that this character is inherited with incomplete dominance of smaller relative weight. The genes determining greater thymus weight are concentrated in the genetic pool of AKR/J and C57BL/6 strains. These genes are characterized by some degree of recessivity with respect to the genes determining smaller thymus weight which are concentrated in the genetic pool of C3H/He and BALB/c strains. The highest concentration of the "plus" and "minus" genes is found in the genetic pools of AKR/J and C3H/He strains respectively.     

Genetic factors at the enterocyte level account for variations in intestinal cholesterol absorption efficiency among inbred strains of mice.

Interindividual and interstrain variations in cholesterol absorption efficiency occur in humans and animals. We investigated physiological biliary and small intestinal factors that might determine variations in cholesterol absorption efficiency among inbred mouse strains. We found that there were significant differences in cholesterol absorption efficiency measured by plasma, fecal, and lymphatic methods: <25% in AKR/J, C3H/J, and A/J strains; 25-30% in SJL/J, DBA/2J, BALB/cJ, SWR/J, and SM/J strains; and 31-40% in C57L/J, C57BL/6J, FVB/J, and 129/SvJ strains. In (AKRxC57L)F1 mice, the cholesterol absorption efficiency (31 +/- 6%) mimicked that of the C57L parent (37 +/- 5%) and was significantly higher than in AKR mice (24 +/- 4%). Although biliary bile salt compositions and small intestinal transit times were similar, C57L mice displayed significantly greater bile salt secretion rates and pool sizes than AKR mice. In examining lymphatic cholesterol transport in the setting of a chronic biliary fistula, C57L mice displayed significantly higher cholesterol absorption rates compared with AKR mice. Because biliary and intestinal transit factors were accounted for, we conclude that genetic variations at the enterocyte level determine differences in murine cholesterol absorption efficiency, with high cholesterol absorption likely to be a dominant trait. This study provides baseline information for identifying candidate genes that regulate intestinal cholesterol absorption at the cellular level.     

Kinetics of ectromelia virus (mousepox) transmission and clinical response in C57BL/6j, BALB/cByj and AKR/J inbred mice

Research was undertaken to answer basic questions on susceptibility, clinical response and transmission of ectromelia virus in selected strains of inbred mice. C57BL/6J and AKR/J were found to be markedly more resistant to a virulent strain of ectromelia virus (isolated during the 1979-80 outbreak at the National Institutes of Health) than C57LJ, BALB/cByJ, DBA/2J, A.By/SNJ and C3H/HeJ when infected by footpad inoculation. In C57BL/6J and AKR/J the LD50 was about 7 logs higher than the ID50. With one exception, C57LJ, the LD50 and ID50 titers in the other strains were about equal. In C57LJ the LD50 titer was intermediate. Following intragastric inoculation, virus was isolated from feces of C57BL/6J mice for as long as 46 days and up to 29 days from BALB/cByJ mice. Transmission to cage mates from intragastrically infected C57BL/6J and BALB/cByJ occurred up to 36 and 30 days respectively after infection. Virus was isolated from the spleen in 2 of 5 BALB/cByJ mice and 1 of 7 C57BL/6J mice tested 95 days after gastric inoculation. Following footpad inoculation, BALB/cByJ mice consistently transmitted virus to cage mates before death at 10-12 days. C57BL/6J mice transmitted between days 8 and 17, but not beyond. Virus was maintained in C57BL/6J mice by exposure to infected cage mates for seven passages, which was the most attempted. Clinical signs in infected C57BL/6J mice were usually subtle or inapparent.     

Association between Tph2 gene polymorphism, brain tryptophan hydroxylase activity and aggressiveness in mouse strains

The brain neurotransmitter serotonin is involved in the regulation of aggressive behavior. The main factor determining the brain serotonin level is the activity of the rate-limiting enzyme in the biosynthesis of the neurotransmitter--tryptophan hydroxylase isoform (TPH) 2 encoded by the Tph2 gene. Recently the C1473G single-nucleotide polymorphism in the Tph2 gene was reported. Here we study the C1473G polymorphism in 10 inbred mouse strains (C57BL/6J, AKR/J, DD/He, C3H/HeJ, YT/Y, BALB/cJLac, CC57BR/Mv and A/He) and demonstrate the association of the polymorphism with brain TPH activity and intermale aggressiveness. TPH activity in the midbrain of mice homozygous for the 1473C allele was higher than that in mice carrying 1473G alleles. A close association of the 1473C allele with increased number of attacks towards another male was found. The results support a link between the C1473G polymorphism in Tph2 gene, tryptophan hydroxylase activity and intensity of intermale aggression.     

Differences in spermatogenesis in cryptorchid testes among various strains of mice

The purpose of the study reported here was to define strain differences in spermatogenesis in cryptorchid testes in mice. Mice of strains A/J, BALB/c, CBA/N, C3H/He, C57BL/6 (B6), ddY and ICR were found to be sensitive to heat stress attributable to experimentally induced cryptorchidism. In contrast, mice of strains AKR/N (AKR), MRL/MpJ-+/+ (M+) and MRL/MpJ-lpr/lpr (lpr) were resistant to heat stress. Relative increases of apoptotic cells were detected in the sensitive group, but not in the resistant group. A decrease of proliferating cell nuclear antigen-immunoreactive cells after experimentally induced cryptorchidism was observed only in the sensitive group. These results suggested that heat stress-resistant germ cells were present in MRL and AKR strains, possibly originating from the genetic background.     

Strain differences of ether susceptibility in mice

The susceptibility to ether in the following six strains of mice was tested: C57BL/6, DBA/2, BALB/c, C3H/He, ICR and ddY. Mice of 4 weeks old were exposed to a flow of air containing various concentrations of ether for 90 min and the mortalities were assessed. The C57BL/6 strain was the most resistant and the C3H/He strain was the most sensitive to the lethal effect of ether. The susceptibilities of the closed colony mice, ICR and ddY, were intermediate between those of C57BL/6 and C3H/He mice. The DBA/2 and BALB/c strains were more sensitive than these closed colony mice and made up a sensitive group with the C3H/He strain. The LD50 values for ether in male mice of C57BL/6 and C3H/He were 6.0 and 3.1% atm, and in female mice of these strains were 6.6 and 3.2% atm, respectively. The ED50 value of ether which was accompanied by loss of righting reflex after exposure for 10 min was also higher in male C57BL/6 mice than in male C3H/He mice.     

Strain difference in mouse natural killer activity augmented by mouse interferon and poly I.C

The level of natural killer (NK) activity was found to vary considerably among several mouse strains. In vivo and in vitro, interferon (IFN) and IFN inducers have been shown to augment mouse NK activity. C3H/He mice showed high NK activity, DDD/1 and A/J mice low NK activity, and C57BL/6, BALB/c and DBA/2 mice intermediate NK activity after injection with polyinosinic polycytidylic acid (poly I. C.). The same NK activity correlation was observed in nontreated mice, but the NK activities were lower compared with the poly I. C.-injected mice. Moreover, the DDD/1 and A/J mice showed almost no augmentation of NK activity on injection with poly I.C. In vivo, C3H/He, BALB/c and C57BL/6 mice injected with IFN showed augmented NK activity, but DDD/1 mice showed no such reaction. In vitro, C3H/He, BALB/c and C57BL/6 mouse spleen cells treated with IFN also showed augmented NK activity, but DDD/1 mouse spleen cells showed almost none. F1 hybrids between high (C3H/He) and low (DDD/1) NK-activity strains showed high NK activity. Thus, activity is dominant over low activity. The segregation of (DDD/1 X C3H/He) Fl X DDD/1 back-cross mice suggested that the strain differences in NK activity are under polygenic control.     

Basal lung mechanics and airway and pulmonary vascular responsiveness in different inbred mouse strains.

Little is known about interstrain variations in baseline lung functions or smooth muscle contractility in murine lungs. We therefore examined basal lung mechanics and airway, as well as vascular reactivity to methacholine, thromboxane (using U-46619), and endothelin-1 (ET-1), A/J, AKR, BALB/c, C3H/HeN, C57BL/6, and SCID mice. All experiments were performed with isolated perfused mouse lungs. Except AKR mice (which were excluded from further analysis), all other strains showed stable pulmonary compliance, pulmonary resistance, and pulmonary arterial pressure within a control period of 45 min. Among these strains, C3H/HeN mice exhibited higher dynamic pulmonary compliance and lower pulmonary resistance, whereas SCID mice had higher baseline pulmonary resistance than the other strains. Concentration-response experiments with methacholine showed a lower airway reactivity for C57BL/6 mice compared with the other strains. Perfusion with 1 microM U-46619 or 100 nM ET-1 revealed a similar pattern: the agonist-inducible broncho- and vasoconstriction was lower in C57BL/6 mice than in all other strains, whereas it tended to be higher in SCID mice. The present study demonstrates a correlation between airway and vascular responsiveness in all tested strains. SCID mice are hyperreactive, whereas C57BL/6 mice are hyporeactive, to smooth muscle constrictors. Lung mechanics, as well as airway and vascular responsiveness, appear to be genetically controlled.     

Studies on pulmonary aryl hydrocarbon hydroxylase activity in inbred strains of mice.

Pulmonary and hepatic levels of aryl hydrocarbon hydroxylase (AHH) were studied in inbred strains of mice following intratracheal (i.t.) instillation of 3-methylcholanthrene (MCA). I.t. instillation of 188 mug MCA in sterile 0.2% gelatin in saline resulted in preferential induction of pulmonary AHH. After treatment with this dose of MCA, the pulmonary AHH levels of strains C57BL/6Cum, C57BL/6J, BALB/cMai, C3H/fMai, and C57L/J were observed to be induced within 24 h after treatment. Strains DBA/2Cum, AKR/J, SJL/J, DBA/2J and RF/J expressed no such increase. At a dose of 500 mug MCA, the pulmonary tissue of DBA/2 mice did express a 4-fold increase. This increase in AHH was determined to be quite different from the increase observed in C57BL/6 mice by: (1) specific activity of the enzymes, (2) genetic regulation, (3) susceptibility to inhibition by 7,8-benzoflavone, and (4) spectral properties of the associated cytochromes. It was of major importance that induction of pulmonary AHH was observed to be regulated by a single dominant gene in crosses involving the C57BL/6Cum and DBA/2Cum strains of mice. Results were discussed with the view in mind that these genetically regulated levels of AHH may play a role in susceptibility to cancers induced by polycyclic aromatic hydrocarbon carcinogens.     

Immune Response against Hamster Erythrocytes in the Low-Responder Mouse Strains

Antibody response against hamster red blood cells (H-RBC) was examined in inbred strains of C57BL/6, AKR, C3H/He, DDD and SL mice, and outbred CF1 mice. 1) There were strain differences in antibody response after a primary intravenous injection of H-RBC. DDD, SL and CF1 mice belonged to high-responder strains, while C57BL/6, AKR and C3H/He to low-responder strains. In the spleens of immunized CF1 and SL, 40 to 70 times as many plaque-forming cells (PFC) as those in C57BL/6 mice were detected. The magnitudes of the response were: CF1 ≒ SL>DDD>>C3H/He ? AKR>C57BL/6. 2) 2-mercaptoethanol resistant (MER) antibody was detected in neither low- nor high-responders after a primary intravenous antigen-injection. 3) After a secondary intravenous antigen-injection, MER antibody was detected in all the SL mice, but only in 30 to 50% of AKR and C57BL/6 mice. 4) A subcutaneous injection of H-RBC in Freund's complete adjuvant (FCA) did not elicit antibody production within 10 days. When mice pre-sensitized 7 days in advance w^Tith H-RBC in FCA were intravenously injected with H-RBC, enhanced antibody production of the primary type was observed in all the mouse strains. 5) In pre-sensitized mice, the extent of the enhancement of antibody production was the highest in low-responder C57BL/6 mice and the lowest in high-responder SL and CF1 strains. Thus, there was no strain difference in antibody titers or the numbers of PFC after the booster.     

Macronutrient diet selection in thirteen mouse strains

The strain distribution for macronutrient diet selection was described in 13 mouse strains (AKR/J, NZB/B1NJ, C57BL/6J, C57BL/6ByJ, DBA/2J, SPRET/Ei, CD-1, SJL/J, SWR/J, 129/J, BALB/cByJ, CAST/Ei, and A/J) with the use of a self-selection protocol in which separate carbohydrate, fat, and protein diets were simultaneously available for 26-30 days. Relative to carbohydrate, nine strains consumed significantly more calories from the fat diet; two strains consumed more calories from carbohydrate than from fat (BALB/cByJ, CAST/Ei). Diet selection by SWR/J mice was variable over time, resulting in a lack of preference. One strain (A/J) failed to adapt to the diet paradigm due to inadequate protein intake. Comparisons of proportional fat intake across strains revealed that fat selection/consumption ranged from 26 to 83% of total energy. AKR/J, NZB/B1NJ, and C67BL/6J mice self-selected the highest proportion of dietary fat, whereas the CAST/Ei and BALB/cByJ strains chose the lowest. Finally, epididymal fat depot weight was correlated with fat consumption. There were significant positive correlations in AKR/J and C57BL/6J mice, which are highly sensitive to dietary obesity. However, absolute fat intake was inversely correlated with epididymal fat in two of the lean strains: SWR/J and CAST/Ei. We hypothesize that the SWR/J and CAST/Ei strains are highly sensitive to a negative feedback signal generated by increasing body fat, but the AKR/J and C67BL/6J mice are not. The variation in dietary fat selection across inbred strains provides a tool for dissecting the complex genetics of this trait.     

Genetic determinants of resistance to ectromelia (mousepox) virus-induced mortality.

Resistance to ectromelia (mousepox) virus-induced mortality was examined in crosses between susceptible DBA/2J, A/J, and BALB/cByJ mice and resistant C57BL/6J and AKR/J mice. Depending on the cross, resistance to mousepox virus was shown to be determined by one or more independently assorting autosomal loci with dominant alleles for resistance in AKR/J and C57BL/6J mice and recessive alleles in A/J, BALB/cByJ, and DBA/2J mice. A sexual dimorphism in resistance to disease was also observed.     

Structural evidence for a polymorphic or allelic form of the heavy chain variable region.

The heavy (H) chains of anti-phosphocholine (PC) antibodies from C57BL/6J and CBA/J were sequenced through the N-terminal 36 residues and compared with previously published sequences of A/J anti-PC antibody and BALB/c PC-binding myeloma proteins T15, M603, and M511. Each of these antibody preparations contained molecules having light (L) chains and idiotypic determinants of T15, M511, and M603 indicating the presence of at least three different anti-PC antibodies in each pool. The structures of the C57BL/6J and CBA/J H chains each revealed a single sequence from positions 1 to 36 (which includes the first complementarity determining region (CDR), and they were identical. The first CDR was identical to that previously found for BALB/c and A/J indicating that this portion of these antibody molecules is highly conserved throughout inbred mice and is probably critical to PC-binding. A surprising finding was that both C57NL/6 and CBA sequence differed from the BALB/c and A/J sequences at two positions, residue 14 and 16. Since each of these strains differs at the allotype locus, the data indicates that the evolution of allotypy in mice occurred after variable region diversity for the particular genes.     

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.     

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.     

Loss ofHindIII cleavage sites in thed-amino acid oxidase gene in some inbred strains of mice

Summary d-Amino acid oxidase cDNA was amplified by a polymerase chain reaction using RNA extracted from the mouse kidney. When digested withHindIII, the cDNAs of the BALB/c and ddY/DAO^– mice were cleaved into two fragments whereas the cDNA of the ddY/DAO⁺ mice was not. Sequencing revealed that nucleotide-471 of the cDNAs was G in the BALB/c and ddY/DAO^– mice whereas it was substituted for C in the ddY/DAO⁺ mice. This base substitution was the cause of the failure of the cleavage of the cDNA of the ddY/DAO⁺ mice.Examination of other strains of inbred mice showed thatd-amino-acid oxidase cDNAs of A/J, AKR, C57BL/6, CD-1, CF#1, ICR, DBA/2, NZB and NZW mice were cleaved withHindIII into two fragments whereas those of C3H/He, CBA/J and NC mice were not. Genomic DNAs extracted from the mice of these 15 strains were digested withHindIII and hybridized withd-amino-acid oxidase cDNA. A 18.2-kb fragment hybridized with the probe in the C3H/He, CBA/J, ddY/DAO⁺ and NC mice whereas two fragments of 12 kb and 6.2 kb hybridized in the other mice. These results are consistent with those of the cDNAs, confirming the loss of theHindIII cleavage site in the C3H/He, CBA/J, ddY/DAO⁺ and NC mice. The Southern hybridization revealed a loss of a differentHindIII cleavage site in the A/J, AKR, C57BL/6, DBA/2, ICR and NZB mice.The substitution at nucleotide-471 should cause a substitution of an amino acid residue. However, this substitution did not affect catalytic activity ofd-amino acid oxidase.     

Chromosomal localization of the loci responsible for dystrophic cardiac calcinosis in DBA/2 mice.

Dystrophic cardiac calcinosis (DCC) occurs in certain inbred strains of mice, including DBA/2 and C3H/He, and is generally found as an incidental lesion in adult animals at necropsy. Preliminary genetic studies into the cause of DCC have been performed in DBA/2 mice and suggest that DCC is inherited as an autosomal recessive trait involving three or four unlinked genes. To investigate the genetics of DCC further, we produced myocardial cell death by freeze-thaw injury to induce DCC. Experiments were conducted with three F1 hybrids made using three inbred strains of mice (DBA/2J and C3H/HeJ, DCC-susceptible strains; C57BL/6J, DCC-resistant strain) to compare the genetic factors in the development of DCC. We found that DBA/2 and C3H/He mice share the same gene pattern(s) that is responsible for DCC. We determined by backcross linkage analysis in DBA/2 and C57BL/6 mice that at least one recessive locus is responsible for DCC. A haplotype analysis of the backcross data demonstrated that the recessive locus, designated dyscalc1, is located on Chromosome 7, 20.5 cM distal to the centromere. The likely candidate genes for dyscalc1 are discussed. Further understanding of the structure and function of these mutant genes will be beneficial in explaining the molecular pathogenesis of DCC.     

Problems in the genetics of stress. II. Genetic analysis of endocrine gland weight in mice under normal conditions and during exposure to stress]

Relative weight of adrenals, thymus, hypophysis and gonads was studied in female mice after 21 days after parturition and in intact males. One group of females was stressed during pregnancy, and another group was intact. All these animals were a progeny of the full diallele cross of 4 inbred mice strains (BALB/c, C3H/He, C57BL/6, AKR/J). On the basis of analysis of general and specific combining ability the conclusion is drawn that the relative weight of the endocrine glands is inherited additively in females of both experimental groups. However, it was found that the size of additive genetic variation for these characters in the population of females, which had been stressed during their pregnancy was larger, than in the control population. A significant role of non-additive genes in the determination of these characters was observed in males. The degree of hypertrophy of adrenals and lysis of thymus in stressed females corresponded to their emotional reactivity. Significant genotypic correlations between the weight of some endocrine glands, on one hand, and the emotional reactivity and the rate of sexual maturation, on the other hand, were found in both experimental groups of females. In the stressed group these correlations were higher.     

Genetic differences in BCG-induced resistance to Schistosoma mansoni are not controlled by genes within the major histocompatibility complex of the mouse.

Induction of nonspecific resistance to Schistosoma mansoni infection after the i.v. injection of viable BCG was investigated in outbred mice and a panel of inbred and H-2 congenic strains. Significant protection was induced in CF1, A/J, C57BL/6, C57BL/10, DBA/2, C57BR, and SJL mice. BALB/c mice were not protected whereas CBA and C3H mice expressed intermediate degrees of protection. Expression of the protective phenomenon is not controlled by genes within the MHC as shown by the marked differences in response between BALB/c and DBA/2 (H-2d) as well as between C57BR and C3H (H-2k) mice. H-2 congenic strains with C57BL/10 background (B10.A and B10.D2) were high responders. BALB.B10 mice carrying the high responder (B10) MHC on the nonresponder (BALB/c) background were not protected. The degree of splenic hypertrophy did not correlate with the expression of nonspecific resistance. These results demonstrate that, in addition to controlling specific immune responses, genetic differences influence the nonspecific protective phenomena related to BCG administration as well.     

Polymorphism of murine endogenous proviruses revealed by using virus class-specific oligonucleotide probes

Inbred mice contain three classes of endogenous nonecotropic murine leukemia virus-related sequences, namely xenotropic, polytropic, and modified polytropic proviruses. Oligonucleotide probes specific for the three different classes were prepared and used to examine the diversity of endogenous sequences present in eight different strains of mice: HRS/J, BALB/cJ, A/J, AKR/J, C57BL/6J, DBA/2J, C57L/J, and C3H/HeJ. A high degree of polymorphism was observed. Overall, the strains showed between 17% (A/J and HRS/J) and 65% (C57BL/6J and C57L/J) shared proviruses, and only four proviruses were present in all eight strains. The similarity among the strains is due in part to the few proviruses present in all of the strains but also represents the independent assortment of a limited set of proviruses. These oligonucleotides provide a basis for determining the stability, distribution, and mutagenic potential of nonecotropic proviruses within the mouse genome.