Genomic variants in an inbred mouse model predict mania-like behaviors

Contemporary rodent models for bipolar disorders split the bipolar spectrum into complimentary behavioral endophenotypes representing mania and depression. Widely accepted mania models typically utilize single gene transgenics or pharmacological manipulations, but inbred rodent strains show great potential as mania models. Their acceptance is often limited by the lack of genotypic data needed to establish construct validity. In this study, we used a unique strategy to inexpensively explore and confirm population allele differences in naturally occurring candidate variants in a manic rodent strain, the Madison (MSN) mouse strain. Variants were identified using whole exome resequencing on a small population of animals. Interesting candidate variants were confirmed in a larger population with genotyping. We enriched these results with observations of locomotor behavior from a previous study. Resequencing identified 447 structural variants that are mostly fixed in the MSN strain relative to control strains. After filtering and annotation, we found 11 non-synonymous MSN variants that we believe alter protein function. The allele frequencies for 6 of these variants were consistent with explanatory variants for the Madison strain's phenotype. The variants are in the Npas2, Cp, Polr3c, Smarca4, Trpv1, and Slc5a7 genes, and many of these genes' products are in pathways implicated in human bipolar disorders. Variants in Smarca4 and Polr3c together explained over 40% of the variance in locomotor behavior in the Hsd:ICR founder strain. These results enhance the MSN strain's construct validity and implicate altered nucleosome structure and transcriptional regulation as a chief molecular system underpinning behavior.

Spontaneous mutant ICR kuru2 might be another shaker-2 deaf mouse

BACKGROUND

We have established a mouse model of spontaneous deafness by sib-inbreeding over 10 years. The mouse was designated as kuru(2) and has been previously reported in this Journal.

MATERIALS AND METHODS

In order to identify the genetic abnormality, the mouse was back-crossed to Mus musculus castaneus (CAST), and myosine 15 or myoXV on chromosome 11 was assumed to be the responsive gene. The background abnormality was identified by gene sequencing.

RESULTS

Deletion of 2446 base pairs occurred in the mouse (from 28795 to 31241 in the complete sequence of the Mus musculus unconventional myosin-15 gene; NCBI accession: AF144093).

DISCUSSION

The myosin ATP-binding site is present in the deleted area. Considering the function that the affected area regulates and previous reports, hearing loss of the examined mouse is attributable to the abnormality of the myoXV gene and this mouse might be another type of shaker-2 deaf mouse.

Putative Chemical Signals about Sex, Individuality, and Genetic Background in the Preputial Gland and Urine of the House Mouse (Mus musculus)

To explore whether preputial gland secretions and/or urine from the house mouse (Mus musculus) can be used for coding information about sex, individuality, and/or the genetic background of strain [ICR/albino, Kunming (KM), and C57BL/6], we compared the volatile compositions of mouse preputial glands and urine using a combination of dichloromethane extraction and gas chromatography coupled with mass spectrometry (GC-MS). Of the 40 identified compounds in preputial gland secretions, 31 were esters, 2 sesquiterpens, and 7 alcohols. We failed to find any compound unique to a specific sex, individual, or strain. However, many low molecular weight compounds between the sexes, most compounds among individuals, and several compounds among the 3 strains varied significantly in relative ratios. These quantitative differences in preputial gland volatiles (analog coding) are likely to convey information about sex, individual, and the genetic background of mouse strain. We identified 2 new main and male-elevated compounds, 1-hexadecanol (Z=3.676, P=0.000, N=19 in ICR; Z=3.576, P=0.000, N=18) and 1-hexadecanol acetate (Z=3.429, P=0.000, N=19 in ICR; Z=3.225, P=0.001, N=18), which were eluted in GC chromatogram after the 2 sesquiterpens. They might also be potential male pheromones, in addition to the well-known E-beta-farnesene and E,E-alpha-farnesene. Additionally, a few compounds including 1-hexadecanol also varied with strains and might also code for genetic information. Of the 9 identified volatile compounds in male urine, (s)-2-sec-butyl-4,5-dihydrothiazole and R,R-3,4-dehydro-exo-brevicomin are known urine-originated male pheromones from previous studies. We also detected 6-hydroxy-6-methyl-3-heptanone, a male urinary pheromonal compound, which had not been directly detected by GC-MS previously. Chemical analysis shows that the genetically more closely related ICR and KM strains had a higher similarity in the volatile compositions of preputial glands and urine than that between ICR or KM and C57BL/6. R,R-3,4-dehydro-exo-brevicomin, in particular, was sensitive to genetic shifts and differed in relative abundance among the 3 strains, whereas (s)-2-sec-butyl-4,5-dihydrothiazole differed between ICR or Km and C57BL/6. Hence, these 2 compounds might code for information about their genetic background.

Comparative Study of Circadian Variation in Numbers of Peripheral Blood Cells among Mouse Strains: Unique Feature of C3H/HeN Mice

We examined strain differences in numbers of blood cells and their circadian rhythms in male Jcl:ICR, BALB/cA, C57BL/6J and C3H/HeN mice. The total numbers of circulating white blood cells (WBCs) were increased during subjective day and night, and the peaks in the active period were common to all strains. However, the number of WBCs in C3H/HeN mice remained lower and plasma levels of corticosterone (CS) were slightly higher throughout the day compared with the other strains. The numbers of circulating red blood cells (RBC) also differed according to strain. The numbers of RBCs, hematocrit (HCT) and hemoglobin (HGB) were considerably lower in C3H/HeN mice compared with the other strains, although mean corpuscular hemoglobin (MCH) and mean corpuscular volume (MCV) were highest among the tested strains. We found that serum erythropoietin (EPO) levels were considerably higher in C3H/HeN mice than in the other three strains. The high EPO level might be related to the unique features of RBCs in C3H/HeN mice. The present observations provide basic information about the numbers of peripheral blood cells and their circadian rhythm in mouse models and also demonstrate a unique feature of C3H/HeN mice.

Baseline and stress-induced plasma corticosterone concentrations of mice selectively bred for high voluntary wheel running

The hypothalamic-pituitary-adrenal (HPA) axis is important in regulating energy metabolism and in mediating responses to stressors, including increasing energy availability during physical exercise. In addition, glucocorticoids act directly on the central nervous system and influence behavior, including locomotor activity. To explore potential changes in the HPA axis as animals evolve higher voluntary activity levels, we characterized plasma corticosterone (CORT) concentrations and adrenal mass in four replicate lines of house mice that had been selectively bred for high voluntary wheel running (HR lines) for 34 generations and in four nonselected control (C) lines. We determined CORT concentrations under baseline conditions and immediately after exposure to a novel stressor (40 min of physical restraint) in mice that were housed without access to wheels. Resting daytime CORT concentrations were approximately twice as high in HR as in C mice for both sexes. Physical restraint increased CORT to similar concentrations in HR and C mice; consequently, the proportional response to restraint was smaller in HR than in C animals. Adrenal mass did not significantly differ between HR and C mice. Females had significantly higher baseline and postrestraint CORT concentrations and significantly larger adrenal glands than males in both HR and C lines. Replicate lines showed significant variation in body mass, length, baseline CORT concentrations, and postrestraint CORT concentrations in one or both sexes. Among lines, both body mass and length were significantly negatively correlated with baseline CORT concentrations, suggesting that CORT suppresses growth. Our results suggest that selection for increased locomotor activity has caused correlated changes in the HPA axis, resulting in higher baseline CORT concentrations and, possibly, reduced stress responsiveness and a lower growth rate.

Human adenosine A(3) receptor leads to intracellular Ca(2+) mobilization but is insufficient to activate the signaling pathway via phosphoinositide 3-kinase gamma in mice

Selective antagonists for the adenosine A(3) receptor (A3AR), a member of the G protein-coupled receptors, have been indicated as potential drugs for anti-asthma or anti-inflammation. However, potent antagonists for the rodent A3AR have not been identified. To evaluate the pharmacological effects of human A3AR antagonists in mice, we here generated A3AR-humanized mice, in which the mouse A3AR gene was replaced by its human counterpart. The expression levels of human A3AR in the A3AR-humanized mice were equivalent to those of mouse A3AR in wild-type mice. Elevation of the intracellular Ca(2+) concentration induced by an A3AR agonist was observed in bone marrow-derived mast cells from the A3AR-humanized mice and this Ca(2+) mobilization was completely antagonized by a human A3AR antagonist. However, antigen-dependent degranulation was not potentiated by the A3AR agonist in the mast cells from A3AR-humanized mice. The agonist-stimulated human A3AR did not lead to the phosphorylation of either extracellular signal-regulated kinase 1/2 or protein kinase B in A3AR-humanized mice. The rate of human A3AR internalization in the mast cells was also markedly decreased compared with that of mouse A3AR in the mast cells. These results demonstrate that the human A3AR is insufficient to activate phosphoinositide 3-kinase gamma-dependent signaling pathways in mice, probably due to the uncoupling of member(s) of the G proteins, which are capable of activating phosphoinositide 3-kinase gamma, to the human A3AR, despite the mouse G protein(s) responsible for the Ca(2+) elevation are coupled with the human A3AR.

Microsatellite Genotyping for Genetic Quality Testing Using Sperm Cells in the Mouse

We attempted to determine the number of sperm cells required for genotyping of one microsatellite marker. The crude genomic DNA extracted from about 760 or more sperm cells gave sufficient quantity of PCR product using a 20 microl-scale PCR. We also studied the effects of non-ionic detergents on extraction of crude sperm genomic DNA. PCR products amplified with the crude sperm genomic DNA extracted using the lysis buffer supplemented with non-ionic detergents showed much clear bands. In conclusion, our results suggest that a small part of the frozen sperm, which is less than 1/10 of the original volume (10 microl), provides sufficient quantity of template DNA for genetic quality testing.

Polymorphic microsatellite markers in the outbred CFW and ICR stocks for the generation of speed congenic mice on C57BL/6 background

Reliable definition of the phenotype of particular alleles is carried out in the genetic background of inbred strains. Appearance of mutations in outbred mice therefore requires the generation of congenic mice. The aim of this study was the establishment of a list of polymorphic microsatellite markers which can be used in a polymerase chain reaction (PCR)-based marker-assisted selection protocol (MASP) to allow the use of the two common outbred stocks, CFW and ICR, as donor animals for the fast generation of congenic C57BL/6 mice. The selection of informative microsatellite markers was carried out to provide a simple evaluation of the PCR products by conventional agarose gel electrophoresis. Outbred mice from three suppliers were examined. In total, 153 microsatellite loci were analysed. Here we present 76 and 70 microsatellite markers polymorphic for the outbred ICR and CFW stocks compared to C57BL/6. At least three microsatellite loci per chromosome were chosen as informative markers for the autosomal genome, giving rise to a maximum marker distance of 58 cM. Thus, additional individual markers have to be selected for the respective outbred mouse which is chosen as a donor animal.

Sleep time following anesthesia in mouse lines selected for resistance or susceptibility to fescue toxicosis

In previous work, a mouse line selected for resistance (R) to fescue toxicosis had higher activities of two hepatic Phase II detoxification enzymes than a mouse line selected for fescue toxicosis susceptibility (S). The primary objective of the present study was to determine whether those same lines also differed in hepatic Phase I enzyme activity, estimated from sleep time (ST) following sodium pentobarbital anesthesia. Additional objectives were to determine whether ST differences between lines were modulated by endophyte-infected fescue in the diet (with or without an enzyme inducer) and whether ST of individual mice was correlated with the effect of a toxin-containing diet on the postweaning growth of those mice. In Exp. I, 24 males from each line were randomly assigned to each of five diets: control (commercial rodent food meal); E+ (50% endophyte-infected fescue seed, 50% control); E+P (the E+ diet supplemented with 1,000 ppm phenobarbital); E- (50% endophyte-free fescue seed, 50% control); and E-P (the E- diet supplemented with 1,000 ppm phenobarbital). After 4 wk on these diets, ST was measured on all the mice. A second ST was recorded on each mouse by randomly sampling one-fourth of the population after 1, 2, 3, or 4 wk on a pelleted rodent food diet. Regardless of diet, R mice had shorter first and second ST than S mice (P < 0.01), suggesting higher hepatic Phase I microsomal enzyme activity. Mice on both phenobarbital-supplemented diets had shorter first ST than mice whose diets did not include that microsomal enzyme inducer (P < 0.01). In Exp. II, ST was measured on male and female R and S mice (n = 280) after they had been fed the E- diet for 2 wk, then the E+ diet for 2 wk, and then a pelleted rodent food diet for 2 wk. Growth response to the E+ diet was the percentage of reduction in gain on the E+ diet compared to gain on the E- diet the previous 2 wk. As in Exp. I, S mice slept longer than R mice (P < 0.01). The residual correlation between ST and gain reduction associated with the E+ diet equaled 0.04. Thus, an animal's apparent Phase I enzyme activity did not predict its growth rate depression on the toxin-containing diet. Based on these and previous studies, divergent selection for toxicosis response in mice was successful partially by causing divergence in activities of hepatic Phase I and II detoxification enzymes.

Evolution of a small-muscle polymorphism in lines of house mice selected for high activity levels

To study the correlated evolution of locomotor behavior and exercise physiology, we conducted an artificial selection experiment. From the outbred Hsd:ICR strain of Mus domesticus, we began eight separate lines, each consisting of 10 breeding pairs. In four of the lines, we used within-family selection to increase voluntary wheel running. The remaining four lines were random-bred (within lines) to serve as controls. Various traits have been monitored to test for correlated responses. Here, we report on organ masses, with emphasis on the triceps surae muscle complex, an important extensor of the ankle. Mice from the selected lines exhibit reduced total body mass, increased relative (mass-corrected) kidney mass, and reduced relative triceps surae mass. In addition, a discrete muscle-mass polymorphism was observed: some individuals had triceps surae that were almost 50% lighter than normal for their body mass. This small-muscle phenotype was observed in only three of the eight lines: in one control line, it has fluctuated in frequency between zero and 10%, whereas in two of the selected lines it has increased in frequency to approximately 50% by generation 22. Data from a set of parents and offspring (generations 23 and 24) are consistent with inheritance as a single autosomal recessive allele. Evidence for the adaptive significance of the small-muscle allele was obtained by fitting multiple-generation data to hierarchical models that include effects of genetic drift and/or selection. The small-muscle allele is estimated to have been present at low frequency (approximately 7%) in the base population, and analysis indicates that strong selection favors the allele in the selected but not control lines. We hypothesize that the small muscles possess functional characteristics and/or that the underlying allele causes pleiotropic effects (e.g., reduced total body mass; increased relative heart, liver, and kidney mass) that facilitate high levels of wheel running. Nevertheless, at generation 22, wheel running of affected individuals did not differ significantly from those with normal-sized muscles, and the magnitude of response to selection has been similar in all four selected lines, indicating that multiple genetic "solutions" are possible in response to selection for high activity levels.

Sleep-time variation for ethanol and the hypnotic drugs tribromoethanol, urethane, pentobarbital, and propofol within outbred ICR mice

To evaluate the phenotypic variation within a commercial outbred mouse stock, we examined sleep-time (or duration of loss of righting reflex) of outbred ICR mice after i.p. injection of ethanol (4.0 g/kg of body weight), urethane (1.3 g), tribromoethanol (250 mg), and pentobarbital (60 mg), and after i.v. injection of propofol (30 mg). We observed high-grade individual differences in sleep-time that ranged from 0 to 179 min, 83.1 +/- 4.3 (mean and SEM of 100 mice) for ethanol; 0 to 169 min, 64.5 +/- 3.1 for pentobarbital; 0 to 160 min, 36.6 +/- 3.6 for urethane; 0 to 120 min, 21.5 +/- 2.2 for tribromoethanol; and 3 to 20.5 min, 7.1 +/- 0.3 for propofol. This extensive phenotypic variance within the outbred stock was as great as the variation reported among inbred strains or selected lines, and the varied susceptibility within the colony was inherited by Jcl:ICR-derived inbred strains IAI, ICT, IPI, and IQI. The range of sleep-time variance for ethanol, pentobarbital, urethane, tribromoethanol, and propofol within four-way cross hybrid Jcl:MCH(ICR) mice was 86.6%, 63.3%, 124%, 61.0%, and 53.1% that of outbred Jcl:ICR mice, respectively. The present study indicates that phenotypic variance within an outbred Jcl:ICR stock was at high risk for susceptibility to the drugs that depress the central nervous system and that Jcl:ICR-derived inbreds may be an excellent source of animal models for studying the anesthesia gene.

Linkage mapping of the mouse nephrosis (nep) gene to chromosome 15

ICGN is a partially inbred strain of mice with nephrotic syndrome caused by spontaneous glomerular lesion. It has been reported that the albuminuria in ICGN mouse was controlled by at least a single autosomal recessive gene (nep). In this study, we mapped the nep locus by linkage analysis of backcross progeny between ICGN and MSM mice using DNA pooling method. The linkage analysis revealed that the nep locus was localized on the distal part of chromosome 15.

Molecular cloning and sequence analysis of C57BL/6 mouse contrapsin cDNA

Contrapsin is a member of the serpin superfamily and inhibits trypsin much more strongly than alpha1-antiproteinase. Mouse and rat contrapsins, however, have similarity in sequence to human alpha1- antichymotrypsin. In order to test the hypothesis that reactive site regions of contrapsin family evolved under strong selective pressure, cDNA sequence of C57BL/6 mouse contrapsin was determined and compared with that of ICR mouse. The cDNA sequence of C57BL/6 mouse contrapsin was found to contain an open reading frame encoding polypeptide consisting of 418 amino acid residues. The work reported in this paper shows that the reactive site is not hypervariable as compared with the rest of molecule.

Genetic selection of mice for high voluntary wheel running: effect on skeletal muscle glucose uptake

Effects of genetic selection for high wheel-running activity (17th generation) and access to running wheels on skeletal muscle glucose uptake were studied in mice with the following treatments for 8 wk: 1) access to unlocked wheels; 2) same as 1, but wheels locked 48 h before glucose uptake measurement; or 3) wheels always locked. Selected mice ran more than random-bred (nonselected) mice (8-wk mean +/- SE = 8,243 +/- 711 vs. 3,719 +/- 233 revolutions/day). Body weight was 5-13% lower for selected vs. nonselected groups. Fat pad/body weight was ~40% lower for selected vs. nonselected and unlocked vs. locked groups. Insulin-stimulated glucose uptake and fat pad/body weight were inversely correlated for isolated soleus (r = -0.333; P < 0.005) but not extensor digitorum longus (EDL) or epitrochlearis muscles. Insulin-stimulated glucose uptake was higher in EDL (P < 0.02) for selected vs. nonselected mice. Glucose uptake did not differ by wheel group, and amount of running did not correlate with glucose uptake for any muscle. Wheel running by mice did not enhance subsequent glucose uptake by isolated muscles.

Hormonal regulation of mitochondrial Tim23 gene expression in the mouse mammary gland

Tim23, a mitochondrial inner membrane protein, is essential for cell viability. Mouse Tim23 cDNA consisted of 1142 nucleotides plus poly(A) at the 3' end. In situ hybridization showed that mammary epithelial cells expressed Tim23 mRNA during pregnancy. In order to examine the hormonal regulation of the Tim23 gene expression at lactogenesis, the quantity of Tim23 mRNA in the mammary gland was determined by the competitive RT-PCR. The level of Tim23 mRNA was low until mid-pregnancy, increased toward the end of pregnancy and was the highest on day 18 of pregnancy. On day 13 of pregnancy, Tim23 mRNA increased 2.7-fold between 8 and 16 h after ovariectomy but this increase was cancelled out by the simultaneous operation of adrenalectomy. In adreno-ovariectomized mice, the administration of cortisol increased Tim23 mRNA 2-fold but with progesterone, the stimulatory action of cortisol was no longer observed. The results indicated that the expression of the Tim23 gene became active in response to glucocorticoid.

Opposing pharmacological actions of cepharanthin on lipopolysaccharide-induced histidine decarboxylase activity in mice spleens

A biscoclaurin alkaloid preparation, cepharanthin (Ceph), is reported to have opposing pharmacological effects, enhancement or depression, on several cells and tissues, although detailed mechanisms remain unclear. Previously, we reported that Ceph enhanced lipopolysaccharide (LPS)-induced histidine decarboxylase (HDC) activity in mice spleens by consecutive pre-administration. In this study, we examined the pharmacological effects on HDC activity of a single Ceph pre-administration to test the influence of the administration method. Consequently, HDC activities were decreased by a single administration 15 minutes before LPS challenge in ddY and ICR mice spleens. Moreover, to further examine this suppressing effect, we employed genetically mast cell-deficient WBB6F1 W/Wv (W/Wv) mice to avoid the influence of mast cells. In W/Wv mice, HDC activity was enhanced, but not in the congenic WBB6F1 +/+ mice. These findings suggest that mast cells influence the depressant effect on HDC activity by a Ceph single administration in mast cell sufficient mice.

Differential longevity in mouse stocks selected for early life growth trajectory

Small body size is associated with superior longevity in several intraspecies comparisons, including dogs bred for specific forms of work, mice and rats fed diets low in calories, rats fed diets low in methionine, and mutant mice whose levels of growth hormone and thyroid hormone are atypically low. To further investigate the interactions among body size, genetic endowment, and longevity, we measured the life span of female mice selectively bred from Institute for Cancer Research stock for differences in rate of body weight gain. These mice were selected for differential rates of growth either early (0-10 days) or later (26-56 days) in the first 2 months of life. The data show a good correlation between the average weight of the stock and its mean longevity, with low body size associated, as predicted, with longer life span. Weight at 3, 6, and 12 months, and weight at peak body weight, are all significant predictors of longevity (among stocks) in univariate regressions; weight at 6 months has the strongest association in stepwise multiple regression. There is no significant correlation between the life span for the stock and the proportion of deaths attributable to neoplasia in this group of mice. The data provide support for the hypothesis that genetic factors that influence early life growth trajectories can have a strong influence on life span. These size-selected mice provide useful tools for analysis of the genetic factors that influence life history parameters, including maturation and aging rates.

Differential effects of MK-801 on cerebrocortical neuronal injury in C57BL/6J, NSA, and ICR mice

1. Antagonists of the N-methyl-D-aspartate (NMDA) glutamate (Glu) receptor, including [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate], dizocilpine maleate (MK-801), injure pyramidal neurons in the posterior cingulate/retrosplenial (PC/RS) cortex when administered systemically to adult rats and mice. 2. These results have, to our knowledge, only been reported previously in Harlan Sprague Dawley albino rats and International Cancer Research (ICR) mice, an outbred albino strain. 3. Male Non-Swiss Albino (NSA) mice, an albino outbred strain, and male C57BL/6J (B6) mice, a pigmented inbred strain, were injected systemically with 1 mg/kg of MK-801 in the first experiment. This dose of MK-801 reliably produces cytoplasmic vacuoles in neurons in layers III and IV of the PC/RS cortex in 100% of ICR mice treated 4. There was a significant difference in the number of vacuolated neurons in B6 and NSA mice, as assessed by ANOVA. The NSA were not significantly different than previously examined ICR mice, but the B6 had fewer vacuolated neurons than either of the two outbred strains. 5. In the second experiment, male NSA, ICR, and B6 mice were injected systemically with a high dose, 10 mg/kg, of MK-801. This dose has been demonstrated to result in necrosis in the same population of neurons injured by lower doses of MK-801. 6. An ANOVA indicated that there was a significant difference among the three strains of mice, and a Fisher's protected t revealed that the B6 mice were significantly different from both the NSA and ICR, but that, with our test, those two strains were indistinguishable. 7. Male ICR, NSA, and B6 mice were tested in the holeboard food search task 5 hours after 1 mg/kg of MK-801. There were significant differences between the strains in performance both pre and posttreatment. The effect of the drug was not statistically significant. 8. These results suggest that there may be a genetically mediated difference in the reaction to NMDA receptor antagonists, a finding which may be important given the NMDA receptor hypofunction hypothesis for the etiology of schizophrenic symptoms.

Graded and areal expression patterns of regulatory genes and cadherins in embryonic neocortex independent of thalamocortical input

The differentiation of areas of the mammalian neocortex has been hypothesized to be controlled by intrinsic genetic programs and extrinsic influences such as those mediated by thalamocortical afferents (TCAs). To address the interplay between these intrinsic and extrinsic mechanisms in the process of arealization, we have analyzed the requirement of TCAs in establishing or maintaining graded or areal patterns of gene expression in the developing mouse neocortex. We describe the differential expression of Lhx2, SCIP, and Emx1, representatives of three different classes of transcription factors, and the type II classical cadherins Cad6, Cad8, and Cad11, which are expressed in graded or areal patterns, as well as layer-specific patterns, in the cortical plate. The differential expression of Lhx2, SCIP, Emx1, and Cad8 in the cortical plate is not evident until after TCAs reach the cortex, whereas Cad6 and Cad11 show subtle graded patterns of expression before the arrival of TCAs, which later become stronger. We find that these genes exhibit normal-appearing graded or areal expression patterns in Mash-1 mutant mice that fail to develop a TCA projection. These findings show that TCAs are not required for the establishment or maintenance of the graded and areal expression patterns of these genes and strongly suggest that their regulation is intrinsic to the developing neocortex.

[Genetic and biological characteristics of noninbred mice from the ICR colony]

Noninbred mice of the ICR colony were studied by a set of characters making it possible to estimate the range of genetic polymorphism in the given population. Genotypes of mice for loci A-, B-, D-, S-, PP, Se Se, and cc were determined. Noninbred mice were polymorphic for loci A, B, D, and S. Frequencies of recessive alleles of loci A, B, and D was calculated. Noninbred mice have a high fecundity and a low level of embryonic mortality, which indicate population heterogeneity. The age of the mother was shown to have no effect on the ovulation norm. The population standard of the colony for age-dependent change in the body weight and size was established. Age-dependent survival in females and males was shown to be associated.

Nonallelic noncomplementation models in mice: the first arch and lidgap-Gates mutations

We tested for complementation between two Mendelian mutations in mice, Far (first arch) and lgGa (lidgap-Gates). Each of these mutations gives greater than 70% risk of the birth defect, open eyelids, in homozygotes and gives little or no risk in heterozygotes. Far and lgGa are known to not be alleles; Far maps to Chr 2 and lgGa maps to Chr 13. However the cross between +/Far (on the BALB/cGaBc strain) and lgGa/lgGa (on the LGG/Bc strain) gave 32% (48/149) of progeny affected with open eyelids at birth: 63% (45/71) of the double heterozygote, +/Far, +/lgGa, compared with 4% (3/78) of the +/+, +/lgGa progeny. That is, the complementation test suggests that Far and lgGa are alleles, whereas the mapping data show that they are not. We interpret the result of the Far by lgGa test as an example of nonallelic noncomplementation (or "false allelism") in mammals, and suggest that this phenomenon might be expected because open eyelids at birth involves a developmental threshold. Our data also show that both the embryonic and the maternal background genotypes strongly influence the risk of open eyelids in the Far by lgGa crosses. The risk to the double heterozygote (+/Far, +/lgGa) is highest (77%) with Far from the BALB/cGaBc rather than the ICR/Bc (0%) strain and in a BALB/cGaBc (77%) rather than an LGG/Bc (50%) dam in the reciprocal cross. This effect of genetic context on risk is also predicted by the threshold model. Based on our data on open eyelids at birth, we suggest that false allelism may be common in mammalian birth defects that result from failure to meet developmental thresholds, even when the "causal" mutations are Mendelian.

Inbreeding and reproduction in mice divergently selected for response to a dietary toxin

This study was conducted to determine whether inbreeding coefficients of selected parents or of progeny differed between lines of mice selected for increased or decreased responsiveness to a nutritional toxicosis. A second objective was to determine whether the influence of inbreeding of parents and/or progeny on reproductive traits differed between those lines. Mice were selected divergently for 8 generations for the effect on post-weaning growth of endophyte-infected fescue seed in their diet. Forty pairs (or in Generation 7, 20 pairs) were selected and mated per generation in each line. Inbreeding increased 0.5 to 0.6% per generation in both lines, a rate close to that predicted from genetic theory. Inbreeding coefficients of selected parents were not higher in the susceptible than in the resistant line. A difference would have been expected if the inbreeding coefficient had been correlated with susceptibility to toxicosis. The magnitudes of inbreeding depression for reproductive traits did not differ significantly between lines. The average inbreeding coefficient of the potential litter tended to be higher in nonfertile than fertile matings (P = 0.10), but inbreeding coefficients of sires and dams did not differ between successful and unsuccessful matings. Inbred litters tended to be born earlier than noninbred litters (P = 0.10). Inbred dams produced smaller litters than noninbred dams (main effect P < 0.05) but only when the litter also was inbred (interaction P < 0.01). Sex ratio was not influenced by inbreeding of sire, dam or litter, but there was a higher proportion of male progeny in the susceptible than in the resistant line (P = 0.01). To avoid reduced reproductive fitness, laboratory animal populations should be managed to minimize inbreeding of progeny and dam.

Analysis of the murine Hoxa-9 cDNA: an alternatively spliced transcript encodes a truncated protein lacking the homeodomain

Hoxa-9 is one of the homeo box (Hox) genes exhibiting similarity to the Drosophila Abdominal B gene. So far, only partial nucleotide sequences have been reported for mouse Hoxa-9 cDNA (Rubin et al., (1987) Mol. Cell. Biol. 7, 3836-3841). Here, we have determined the nucleotide sequence of the 5'-region of mouse Hoxa-9 cDNA and its genomic structure. Mouse Hoxa-9 cDNA contains a complete ORF encoding a protein of 271aa exhibiting 96.7% identity to its human counterpart. Interestingly, an alternatively spliced transcript (Hoxa-9T) was identified by RT-PCR. Sequence analysis revealed that 173bp within the Hoxa-9 ORF was missing from the Hoxa-9T cDNA. This additional splicing would potentially result in a frameshift, leading to the production of a truncated protein lacking the homeobox. Northern blot analysis revealed that the probe containing the homeodomain hybridized to two major transcripts (2.5 and 1.9kb) in the trunk region of 12.5 dpc embryos, and adult kidney and large intestine. On the other hand, the probe containing the additional intron detected only 2.5kb transcript in the same tissues, indicating that 1.9kb transcript corresponds to Hoxa-9T mRNA. We have also determined the transcriptional start site of Hoxa-9T.

Growth and physiological responses to toxicosis in lines of mice selected for resistance or susceptibility to endophyte-infected tall fescue in the diet

In three experiments, mice from lines selected for resistance (R) or susceptibility (S) to growth depression from endophyte-infected fescue seed in the diet were fed diets containing infected (E+) or non-infected (E-) seed. Activities of liver enzymes known to participate in oxidation, reduction, or hydrolysis or in conjugation of xenobiotics were measured in these mice. In all experiments, E+ caused greater reduction in initial ADG of S than of R mice. In Exp. 1, liver cytochromes P450 and b5 activities were not affected by line, diet, or their interaction. These enzymes were not evaluated in subsequent experiments. In all experiments, glutathione-S-transferase (GST) and uridine diphosphate glucuronosyltransferase (GRT) activities differed between lines. Resistant mice had significantly higher GST activity on both diets in Exp. 1, on E- in Exp. 2, and on E+ in Exp. 3. Resistant mice had higher GRT activities on E+ in Exp. 1, on E- in Exp. 2, but after 4 wk on either diet in Exp. 3. Before test diets were imposed in Exp. 3, GST and GRT activities were higher in R-line mice. Divergent selection created lines that differed in response to tall fescue in the diet. Postweaning growth of resistant mice was less severely depressed by E+, although susceptible mice later expressed compensatory gain. Activities of two detoxification enzymes generally were higher in livers from R-line mice, suggesting a biochemical mechanism for the difference. Using such traits, it may be possible to select ruminants for resistance to fescue toxicosis.

Selection for growth does not affect apparent energetic efficiency of jejunal glucose uptake in mice

Five-wk-old male mice from high growth (M16) and randomly bred control (ICR) lines, plus their reciprocal crosses, ICR x M16 and M16 x ICR, were used to investigate whether whole-body O2 consumption, jejunal respiration, jejunal glucose absorption and the apparent energetic efficiency of jejunal active glucose uptake in mice are altered by genetic selection for growth as well as by heterosis and maternal effects. Whole-body O2 consumption was measured in 12 mice from each line or cross. The mice were later killed for measurement of jejunal O2, using tissue respiration chambers and jejunal glucose transport determined by 3H-3-O-methylglucose accumulation. No heterosis or maternal effects were detected in jejunal glucose active transport and active glucose uptake. Selection for growth (M16 vs. ICR) increased daily gain (1.54 vs. 1.09 g, P < 0.001), small intestinal length and weight, but did not enhance jejunal glucose transport. The apparent energetic efficiency of jejunal active glucose uptake among lines was not different (54.0, 50.4, 51.6 and 47.1 nmol ATP expended/nmol glucose uptake for M16, ICR, M16 x ICR and ICR x M16, respectively, P > 0.63). Selection for growth in mice did not result in more energetically efficient jejunal glucose absorption.

Cloning of the cDNA encoding mouse PP5/TFPI-2 and mapping of the gene to chromosome 6

Placental protein 5 (PP5)/tissue factor pathway inhibitor-2 (TFPI-2) is a new homologue of TFPI, which contains three tandemly repeated Kunitz-type proteinase inhibitory (KPI) domains and potently inhibits the extrinsic blood coagulation cascade. In this study, mouse PP5/TFPI-2 cDNA was cloned using a human PP5/TFPI2 cDNA fragment as a probe. The characteristic three KPI domains with short spacer sequences and a basic amino acid stretch in the carboxyl-terminal region present in human PP5/TFPI-2 were well conserved in mouse PP5/TFPI-2. In general, the P1 reactive site residues of active KPI domains are basic amino acids. However, the putative P1 residues of the first, second, and third KPI domains were glutamine, aspartic acid, and serine, respectively. Mouse PP5/TFPI-2 mRNA was highly expressed in developing placenta as in humans. Adult liver and kidney also contained a significant amount of its transcripts. The mouse PP5/TFPI-2 gene was found to be located in the R-positive A2 band by the direct R-banding FISH and identified at 2.7 cM proximal to D6Mit 1 by interspecific backcross analysis.

Expression of the recombinase-activating gene (RAG-1) in murine early embryogenesis

The recombinase activation genes, RAG-1 and RAG-2, are expressed together in immature T or B lymphocytes and possess activity to induce V(D)J rearrangement in T cell receptor (TCR) and Ig genes. In vertebrates, only Ig and TCR molecules are reported to have recombination in their development using multiple V, D, J component gene segments. Thus, expression of RAG genes are localized only in lymphoid organs and sites of extrathymic T cell differentiation. In this study, we have used RAG-1 and RAG-2 genes as markers of possible genetic recombination in developing murine preimplantation embryos, using the highly sensitive reverse transcriptase polymerase chain reaction (RT-PCR) technique and in situ hybridization. From 40 preimplantation embryos of various developmental stages we extracted RNA, reverse-transcribed it into cDNA and used it in RT-PCR studies. A PCR of 35 cycles disclosed expression of RAG-1 but not RAG-2 in morulae and blastocysts. Southern blot hybridization using a specific synthetic oligonucleotide probe for RAG-1 and RT-PCR with another primer pair identified RAG-1 expression in developing embryos. In situ hybridization using a cooled CCD camera also revealed localization of RAG-1 mRNA in blastocysts. We propose possible genetic recombination during late preimplantation murine embryogenesis which may contribute to the loss of totipotency and differentiation of inner cell mass and trophoectoderm.

Morphological studies on the kidney of the spontaneous nephrotic (ICGN) mice in the late stage

Spontaneous nephrotic (ICGN) mice develop proteinuria, hypoproteinemia and hypercholesterolemia. These symptoms steadily progress to chronic renal failure. Details of the changes of the kidney, in the late stage (more than 5 months old) were investigated by both light and electron microscopy. The kidney exhibited a slightly whitish, granular surface and the cortex became thinner and contained fibrous lesions, in which clusters of unaffected and occluded renal tubules were randomly scattered. In the juxtamedullary and outer medullary zone, there were highly dilated renal tubules, which sometimes contained urinary casts. The glomerulus exhibited basement membrane thickening in the capillary loops and the capillary lumen was narrowed in size and sometimes occluded. No detachment of the podocyte from the basement membrane was observed and the podocyte foot-processes were extensively fused, causing their characteristic slits to be lost. The thickened basement membranes were found both in the glomerulus and around the occluded renal tubules, while the basement membrane in the dilated renal tubule appeared normal. Therefore, the basement membranes of the glomerulus and renal tubules appear to react differently in the pathogenesis of the condition. In conclusion, ICGN mice are a good model for not only the nephrotic syndrome but also for chronic renal failure.

Mouse and human chromosomal assignments of mortalin, a novel member of the murine hsp70 family of proteins

Mortalin has been shown to exhibit differential distributions in cells with mortal and immortal phenotypes. In the present study, we report mot-2 cDNA cloning from RS-4 cells--an immortal clone from CD1-ICR mouse embryonic fibroblasts--and the chromosomal assignments of mortalin related genes to mouse chromosomes 18 and X by fluorescence in situ hybridization. Similar analysis assigned the gene to chromosome 5q31.1 in human.

Increased incidence of unpartnered single chromatids in metaphase II oocytes in 39,X(XO) mice

Since rare cases of sex chromosome anomalies such as XXX and XXY were observed in the offspring of our XO breeder mice, we performed a cytogenetic analysis of metaphase II oocytes of XO mice to determine whether any changes in chromosomal configurations occur. We found a significantly increased incidence of unpartnered single chromatids in metaphase II oocytes of XO mice. Such single chromatids may contribute to embryonic aneuploidy. In addition, the tendency of the X-chromosome to segregate non-randomly to the oocyte rather than to the polar body was confirmed.

Chromosomal mapping of mouse 5S rRNA genes by direct R-banding fluorescence in situ hybridization

The mouse 5S rRNA gene was mapped by direct R-banding fluorescence in situ hybridization (FISH) with biotinylated probes. Two genomic fragments amplified by PCR from total genomic DNA of BALB/c mice and Mus spretus, a 0.16-kb fragment that included the 121-bp 5S rRNA gene and a 1.6-kb fragment that included the whole spacer region, were used for chromosomal mapping of the 5S rRNA gene. Both fragments hybridized to a single locus on a pair of autosomal chromosomes of BALB/c mice. The major cluster of mouse 5S rRNA genes was assigned to the most terminal R-negative to R-positive bands of the E region of mouse Chromosome 8, which is homologous to the linkage of the 5S rRNA gene on the long arm of human chromosome 1. The location of the 5S rRNA gene was mapped in five laboratory strains, in wild mice of six Mus musculus subspecies (domesticus, brevirostris, musculus, bactrianus, castaneus, and molossinus) derived from 10 separate localities, and in four different Mus species (spretus, hortulanus, spicilegus, and caroli), using FISH. The 5S rRNA cluster mapped to the same position on the chromosomes of all mouse species and subspecies studied. These results suggest that the location of the mouse 5S rRNA gene on the distal telomeric region of Chromosome 8 is evolutionarily conserved. In comparison, the chromosomal assignments of centromeric 18S-28S rRNA genes are highly variable among the different M. musculus subspecies and Mus species.

Spontaneous immortalization of mouse fibroblasts involves structural changes in senescence inducing protein, mortalin

Mortalin, a novel member of mouse heat shock protein 70 (hsp70) family, is seen to distinguish the cellular mortal and immortal phenotypes by virtue of its cytosolic and perinuclear distribution, respectively. We report here that the cytosolic and perinuclear forms of mortalin from CD1-ICR mouse embryonic fibroblasts and NIH 3T3 cells, respectively, differ by two amino acids, can be distinguished on two-dimensional SDS-polyacrylamide gel. The perinuclear mortalins from RS-4 and Balb/c 3T3 cells harbor the same two amino acids as that of NIH 3T3 cells. However, these when analyzed with C-MEF mortalin did not exhibit the mobility shift equivalent to C-MEF and NIH 3T3 mortalins. The data indicate that the perinuclear mortalin from different immortal fibroblasts are not identical and implicate the possibility of additional structural changes in mortalin during immortalization. Such differences may also contribute to the differential in vitro growth characteristics of these immortal cells.

Murine Cdx-4 bears striking similarities to the Drosophila caudal gene in its homeodomain sequence and early expression pattern

A third member of the murine caudal-like gene family, Cdx-4, has been isolated. In situ hybridization and immunohistochemistry have been used to study the localization of mRNA and protein during murine embryogenesis. Cdx-4 is expressed transiently from 7.0 d.p.c. (days post coitum) until 10 d.p.c., starting at the beginning of gastrulation (7.0-7.5 d.p.c.) in the allantois and posterior tip of the primitive streak. At the mid-streak stage, Cdx-4 expression moves rostrally, and protein and mRNA are detected in all cells over the posterior half of the primitive streak. As development proceeds, Cdx-4 gene products continue to be restricted to the posterior of the embryo, including the remnants of the primitive streak. Cdx-4 is expressed in neurectoderm, presomitic and lateral plate mesoderm, and hindgut endoderm, but the anterior boundary in the paraxial mesoderm is staggered with respect to the other germ layers. At all stages analyzed, Cdx-4 exhibits a graded expression pattern with a posterior maximum, a distribution highly reminiscent of the Drosophila caudal gene. These data add to the recently described distributions of other vertebrate caudal-like genes, and further support the idea that members of this homeobox gene subfamily have regulatory roles in the specification of anteroposterior axial polarity in early embryos.

Cloning and functional expression of a cDNA encoding the mouse beta 2 subunit of the kainate-selective glutamate receptor channel

The primary structure of the mouse glutamate receptor beta 2 subunit has been deduced by cloning and sequencing cDNA. The beta 2 subunit has structural characteristics common to the subunits of glutamate-gated ion channels. Expression of the cloned cDNA in Xenopus oocytes yields functional glutamate receptor channels selective for kainate.

Susceptibility of newly established mouse strain MPS to Mycoplasma pneumoniae infection

A newly established mouse strain, MPS, which is more sensitive to Mycoplasma pulmonis than ICR, ddY and other mouse strains was examined for its susceptibility to Mycoplasma pneumoniae. In experimental infections with M. pneumoniae, it was observed that M. pneumoniae attached to tracheas of MPS mice, and M. pneumoniae cells were isolated from tracheas and lungs of MPS mice even after four weeks of infection, while no mycoplasmas were isolated from ICR and ddY mice after one week of infection. Specific antibodies against M. pneumoniae were also observed by the Western blotting in the sera of MPS mice infected with M. pneumoniae. Although any lung lesion could not be observed in this work, this newly established mouse strain MPS may be useful for experiments of M. pneumoniae infection, especially for the analysis of strain differences in susceptibility to M. pneumoniae infection.

Effect of heterosis on performance of mice across three environments

Performance of six genetic groups of mice was studied in three different environments in order to determine the effect of heterosis on consistency of performance in varied environments. Designed as a 3 x 6 factorial, data were analyzed using least squares analyses of variance. Genetic group effects, environmental effects, genetic group x environment interaction, and heterosis were examined for 42-d weight, age and weight at vaginal opening, age and weight at puberty, ovulation rate (determined by total corpora lutea), number of implantations, and number of fetuses at 10 d of gestation. Weight at vaginal opening, ovulation rate, implantation rate and total number of fetuses exhibited significant heterosis. Regression of these traits against an environmental index (mean performance of all genetic groups over environments) provided an estimate of stability of performance. In general, genetic groups exhibiting heterosis expressed more consistent performance across environments than pure lines did. We conclude that a stability model could be used to aid in identification of lines with consistent performance for production traits in variable environments.

Selection of mouse strains showing high and low incidences of alloxan-induced diabetes

To produce an experimental model of diabetes in animals, ICR mice were inbred until the 20th generation by two-way selection toward the high- and low-incidences of alloxan-induced diabetes. Changes in successive generations in the incidence of such diabetes, in blood glucose levels, growth patterns and reproductive performance were studied. The incidence of alloxan-induced diabetes was 41.1% in the basal population; in the high-incidence strain, it was 98.7% in F13, ranging between 90 and 99% in later generations; and in the low-incidence strain, it reached 0% in F7, remaining near that level in later generations. The heritability of the incidence of alloxan-induced diabetes determined at the beginning of selection was 50-60%. The blood glucose level was 251 +/- 19 mg/dl in the basal population; in the high-incidence strain, it was 423 +/- 11 mg/dl in F13, ranging thereafter between 340 and 455 mg/dl; and in the low-incidence strain, it was 128 +/- 4 mg/dl in F7, then varying from 120 to 140 mg/dl in following generations. The heritability of the blood glucose level determined at the beginning of selection was 40-60%. No marked decrease in growth or reproductive performance accompanied successive selections. Successive generations of the high-incidence mice, however, tended to become heavier than the low-incidence animals. The high- and low-incidence strains, established in the 20th generation, were named the ALS (alloxan-induced diabetes-susceptible) and ALR (alloxan-induced diabetes-resistant) strains, respectively.

Genetic control of survival of frozen mouse embryos

Lines of mice selected for increased litter size (L+), increased body weight (W+), or randomly (K) were used to study genetic variation in embryo cryosurvival in response to standard cryopreservation protocols. A total of 60528-cell embryos from 400 females were used in two studies. In Study 1, embryos from L+, W+, and K were frozen by slow-cool and ultrarapid (direct-plunge) methods to evaluate effects of selection on cryosurvival and genotype X freezing method interaction. Post-thaw survival (PTS) was measured as percentage of recovered embryos developing in vitro to blastocyst per donor female. Nonfrozen control embryos developed similarly for each line. Within slow-cool freezing, lines differed (W+ greater than K, W+ = L+, L+ = K; p less than 0.05); no differences were observed within the ultrarapid freezing. However, line X method interaction effects on PTS were not significant. In Study 2, reciprocal crosses were made between L+ and K and between W+ and K. Hybrid and pure line embryos were frozen by slow-cooling. Control embryos developed similarly for all genotypes. Selection lines did not differ for overall PTS. However, hybrid embryos from L+ dams were superior to those from K dams (84 vs. 61%; p less than .001). No overall embryo heterosis was observed. Differences were not significant among embryo genotypes or treatments for cell number or in vivo survival. These results demonstrate significant correlated responses in embryo post-thaw cryosurvival due to selection, and implicate both maternal and embryonic genomes as controlling mouse embryo cryosurvival.

A single recessive non-MHC diabetogenic gene determines the development of insulitis in the presence of an MHC-linked diabetogenic gene in NOD mice

To study the genetic control of insulitis in non-obese diabetic (NOD) mice, we performed breeding studies in crosses of NOD with non-diabetic strains, ICR-L-line Ishibe (ILI), non-obese non-diabetic (NON) and C3H/He mice. The ILI mouse serologically shared the same MHC Class I and Class II as the NOD mouse. Insulitis was defined as islets invaded by lymphoid cells. Periductular, perivascular and peri-insular lymphoid cell infiltrations were often observed in NOD mice and appear to be the initial lesion leading to insulitis. Such lesions, however, were found in 1-year-old ICR, ILI, NON and Cataract Shionogi (CTS) mice of the NOD's sister strain. The lymphoid cells did not invade the islets in ICR, ILI, NON and CTS mice. The incidence of insulitis was 0% in F1 generations and 40% in female backcrosses (BC) [(ILI x NOD)F1 x NOD] at 9 weeks of age, 48 and 50% in BC[(NON x NOD)F1 x NOD] and BC[(C3H/He x NOD)F1 x NOD] at 1 year of age, respectively. Backcross animals were typed for the MHC to investigate correlation between the development of insulitis and MHC haplotypes. Among the backcross females with insulitis, approximately half the animals were heterozygous for MHC(non/nod) in BC[(NON x NOD)F1 x NOD] and MHC(k/nod) in BC[(C3H x NOD)F1 x NOD]. Among the backcross females with no insulitis, approximately half the animals were homozygous for MHC(nod/nod) in BC[(NON x NOD)F1 x NOD] and in BC[(C3H x NOD)F1 x NOD]. The results suggest that a single recessive non-MHC diabetogenic gene determines the development of insulitis regardless of NOD MHC homozygosity or heterozygosity.

Lethal burn-induced bacterial translocation: role of genetic resistance

Since genetic factors may influence outcome after trauma or during infection, the current experiments were performed to examine the resistance of three genetically different mouse strains to burn-induced bacterial translocation. Outbred ICR, inbred Balb/c, and inbred C57/B1 mice, with a normal or disrupted (monoassociated with Escherichia coli C25) GI tract microflora, were subjected to sham or actual 25% body burns. In Balb/c, but not ICR mice, replacing the normal intestinal microflora with E. coli C25 converted the thermal injury from a nonlethal (0% mortality) to a lethal (68% mortality) injury. The increased mortality of the burned Balb/c mice monoassociated with E. coli C25 was associated with a higher incidence (p less than 0.05) and magnitude (p less than 0.05) of E. coli C25 translocation from the GI tract. The C57/B1 mice were intermediate between the Balb/c and ICR strains, in that C57/B1 mice monoassociated with E. coli C25 had a higher mortality and greater E. coli C25 translocation than mice with a normal microflora after thermal injury. Thus the composition of the intestinal microflora as well as the genetic background of the host influence the susceptibility of the host to burn-induced bacterial translocation and survival.

Genetic analysis of the cause of exencephaly in the SELH/Bc mouse stock

A new mouse stock, SELH/Bc, having a high liability to exencephaly has been developed. About 17% of SELH fetuses are exencephalic. The genetic cause of this exencephaly was investigated in a cross to a normal related ICR/Bc strain and in subsequent classical genetic crosses (F2, first and second backcrosses). The data were compared with a number of genetic models, including that of a single recessive mutation with 17% penetrance. The data did not fit single-locus inheritance. The expectations from the multifactorial threshold model based on an underlying quantitative liability trait with additive inheritance were found to fit the data very well. The number of loci involved was estimated to be about two or three. About 70% of exencephalic SELH fetuses are female, and there is no overall deficiency of males. The relatively higher risk in females was constant across the genetic backgrounds in the experiment. In summary, the liability to exencephaly in SELH mice appears to be a multifactorial threshold trait, and it therefore resembles human neural tube defects in type of genetic etiology. SELH therefore may be a valuable animal model in the study of neural tube defects.

Rodent common fragile sites: are they conserved? Evidence from mouse and rat

Nineteen fragile sites induced by aphidicolin in lymphocyte cultures from the laboratory mouse are documented. These sites are compared with previously described fragile sites induced in mouse fibroblast systems, and then with those reported on chromosomes which have been evolutionarily conserved between the mouse and the laboratory rat. Of a total of 38 fragile sites thus far identified in mouse fibroblasts and lymphocytes, only 4 sites are common to the two cell types; 34 sites show no correspondence of loci. The reason for this discrepancy is unclear, but it is possible that these data may indicate some degree of tissue specificity of fragile site expression in the mouse. Eight autosomes in the mouse and rat retain straightforward and nearly complete banding homology. To test the hypothesis that fragile sites are conserved between the two species, we compared these eight autosomes with regard to number and distribution of fragile site loci. A total of 30 fragile sites is distributed over the conserved chromosomes. Only 4 (possibly 5) are common to both species; 18 are found in the rat but not the mouse, and 4 are found in the mouse but not the rat. Of the 4 shared sites, notable differences in frequency of expression exist. Our comparisons show that: (1) a small number of fragile sites is conserved; (2) a large number of fragile sites is not conserved, and (3) some sites which are conserved are quite different in the frequency at which they are expressed in the two species, indicating that the sites themselves may have undergone evolutionary change.(ABSTRACT TRUNCATED AT 250 WORDS)

A developmental-genetic analysis of aggressive behavior in mice (Mus musculus): III. Behavioral mediation by heightened reactivity or immobility?

This research was designed to investigate development and behavioral mediation in lines of ICR mice that have been selectively bred for aggressive behavior. General behavioral reactivity and behavioral immobility have been implicated as potential mediators by prior analyses of preattack interactions. To evaluate the separate roles of these dispositions, the emergence of attacks in genetically selected lines was tracked for 11 years by three levels of analysis: over successive generations, over development, and over dyadic interactions. Convergent outcomes were observed in all three levels with respect to two findings: (a) Robust line differences were obtained in attack behaviors, and (b) strong associations were found between line differences in attacks and line differences in behavioral immobility. Conversely, all three levels of analysis indicated a weak and inconsistent association between line differences in attacks and measures of social and nonsocial reactivity.

Strain differences in early mouse embryo development in vitro: role of the nucleus

Mouse embryos of many strains are blocked in development at the two-cell stage when placed in culture at the one-cell stage. If, however, they are placed in culture at the two-cell stage, they develop to blastocysts at a high rate. We investigated the transcriptional and translational systems in blocked embryos by assaying enzymatic activity of the protein product of an injected gene and found these systems to be functioning normally. The role of the nucleus was investigated by reciprocal nuclear transplants between blocked and nonblocked embryos. The results indicate that the source of the nucleus was of equal importance to that of the cytoplasm for the successful development of embryos cultured from the one-cell stage. When cultured from the two-cell stage, however, the nucleus was solely responsible for strain differences in culture rates.

Cloning and characterization of a cDNA coding for mouse placental alkaline phosphatase

Mouse alkaline phosphatase [ALP; orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1] was partially purified from placenta. Data obtained by immunoblotting analysis suggested that the primary structure of this enzyme has a much greater homology to that of human and bovine liver ALPs than to the human placental isozyme. Therefore, a full-length cDNA encoding human liver-type ALP was used as a probe to isolate the mouse placental ALP cDNA. The cloned mouse cDNA is 2459 base pairs long and is composed of an open reading frame encoding a 524-amino acid polypeptide that contains a putative signal peptide of 17 amino acids. Homology at the amino acid level of the mouse placental ALP is 90% to the human liver isozyme but only 55% to the human placental counterpart. RNA blot hybridization results indicate that the mouse placental ALP is encoded by a gene identical to the gene expressed in mouse liver, kidney, and teratocarcinoma stem cells. This gene is therefore evolutionarily highly conserved in mouse and human.

Rejection of bone marrow allografts by mice with severe combined immune deficiency (SCID). Evidence that natural killer cells can mediate the specificity of marrow graft rejection

C.B-17 scid (H-2d) mice are homozygous for the gene that causes severe combined immune deficiency (SCID). These mice have no T or B cell function, yet display normal natural killer (NK) activity. Irradiated SCID mice were challenged with marrow grafts to determine if antibodies are necessary for marrow allograft rejection. SCID mice rejected H-2/Hh-1 allogeneic marrow grafts. Moreover, this rejection capability could be adoptively transferred using SCID marrow as a source of NK progenitors infused into irradiated B6 (H-2b) hosts. We conclude that NK cells can mediate marrow allograft reactivity in the absence of immunoglobulin. It follows that NK cells probably have specific receptors for Hh antigens.