Use of Two-Dimensional Electrophoresis to Identify and Map New Mouse Genes

Cytosol polypeptides from mouse liver have been examined using two-dimensional electrophoresis. About 250 spots were readily discernible. When cytosols from strains BALB/cBy and C57BL/6By were compared eight genetically determined differences were observed. Other strain pairs show comparable numbers of differences. These eight phenotypes were scored in seven recombinant inbred lines derived from the two parental strains, and their strain distribution patterns were compared with previously determined patterns for other genetic markers that differ between the two progenitor strains. Using this information, tentative chromosomes assignments for the genes controlling five of the variant phenotypes have been made, and two of the assignments have been confirmed using congenic resistant strains. These eight genes will be useful reference markers in future crosses designed to map new genes.     

The AXB and BXA set of recombinant inbred mouse strains

The recombinant inbred (RI) set of strains, AXB and BXA, derived from C57BL/6J and A/J, originally constructed and maintained at the University of California/San Diego, have been imported into The Jackson Laboratory and are now in the 29th to 59th generation of brother-sister matings. Genetic quality control testing with 45 proviral and 11 biochemical markers previously typed in this RI set indicated that five strains had been genetically contaminated sometime in the past, so these strains have been discarded. The correct and complete strain distribution patterns for 56 genetic markers are reported for the remaining RI strain set, which consists of 31 living strains and 8 extinct strains for which DNA is available. Two additional strains, AXB 12 and BXA 17, are living and may be added to the set pending further tests of genetic purity. The progenitors of this RI set differ in susceptibility to 27 infectious diseases as well as atherosclerosis, obesity, diabetes, cancer, cleft palate, and hydrocephalus. Thus, the AXB and BXA set of RI strains will be useful in the genetic analysis of several complex diseases.     

Evaluation of LEXF/FXLE rat recombinant inbred strains for genetic dissection of complex traits.

Recombinant inbred (RI) strains are formed from an outcross between two well-characterized inbred stains followed by at least 20 generations of inbreeding. RI strains can be utilized for the analysis of many complex phenotypic traits. The LEXF/FXLE RI strain set consists of 34 RI strains derived by reciprocal crossing of LE/Stm and F344/Stm. Here we report on genetic dissections of complex traits using this RI set and their parental strains. We have developed strain distribution patterns for 232 informative simple sequence length polymorphism markers. The framework map covers the rat genome except for chromosome Y. Seventy-six phenotype parameters, which included physiological and behavioral traits, were examined for these RI lines. Quantitative trait locus (QTL) analysis of these parameters revealed 27 significant and 91 suggestive QTLs, illustrating the potential of this RI resource for the detection of underlying gene functions for various phenotypes. Although this RI set was originally developed to study susceptibility to chemical-induced tumors, it has been shown to be equally powerful for a wide spectrum of traits. The LEXF/FXLE RI strains have been deposited at the National Bio Resource Project for the Rat in Japan and are maintained under specific pathogen-free conditions. They are available at http://www.anim.med.kyoto-u.ac.jp/nbr.     

Recombinant congenic strains derived from A/J and C57BL/6J: a tool for genetic dissection of complex traits

Complex genetic traits can be dissected in mice, using well-defined sets of recombinant inbred strains, congenic strains, and recombinant congenic strains (RCS). We report the creation of a series of 37 independent RCS derived from the commonly used inbred strains of laboratory mouse A/J (A) and C57BL/6J (B6). These RCS were derived by systematic inbreeding of independent pairs of animals from a (F1 x A) x A and a (F1 x B) x B double backcross (N3), to create AcB and BcA strains, respectively. Fifteen AcB strains and 22 BcA strains at between 18 and 30 generations of inbreeding have been generated, are healthy, and show stable breeding performance. These strains have been genotyped for a total of 625 informative microsatellite DNA markers covering the entire genome, with an average spacing of 2.6 cM. Haplotype analyses indicate that on average, AcB and BcA strains contain 13.25% of the donor genome, a value close to the 12.5% expected from the breeding scheme used in their creation. In the AcB set, approximately 79% of the B6 genome has been transferred in independent strains, while in the BcA set approximately 84% of the A genome is represented on the B6 background. This represents an excellent coverage of congenic segments from both parental genomes in the two sets of strains, which can now be used to map simple and complex traits in a genome-wide fashion. As an example of the power of AcB/BcA strains as a mapping tool, the 37 strains were typed for susceptibility to infection with Legionella pneumophila, a monogenic trait controlled by the Lgn1 locus on Chromosome 13. Analysis of the strain distribution pattern of L. pneumophila susceptibility allowed direct mapping of Lgn1 to a 3-cM interval. The AcB/BcA set should prove a useful tool with which to investigate the complex genetic basis of known interstrain differences between A and B6 for many important diseases.     

A parametric analysis of factors affecting acquisition and extinction of contextual fear in C57BL/6 and DBA/2 mice

Behavioral analyses of genetically modified and inbred strains of mice have revealed neural systems and molecules that are involved in memory formation. Many of these studies have examined memories that form in contextual fear conditioning, in which an organism learns that a particular context signals the occurrence of a footshock. During fear extinction, nonreinforced exposure to the context results in the loss of the conditioned fear response. The study of extinction has been instrumental for behavioral and molecular theories of memory. However, many of the transgenic, knockout, and inbred strains of mice that have been widely studied in memory have behavioral deficits in contextual fear conditioning, which makes the study of extinction in these mice particularly challenging. Here we explore several strategies for studying extinction in C57BL/6 and DBA/2 mice, two strains known to differ in contextual fear conditioning. First, we attempt to equate performance prior to extinction through several extensive conditioning protocols. Second, we examine extinction in subsets of mice matched for initial levels of context conditioning. Third, we examine within-strain effects of variables known to affect extinction. Differences between the strains persisted across extensive conditioning and extinction protocols, but both strains were sensitive to session duration and context manipulations during extinction. We describe the implications of our results for behavioral and neurobiological approaches to extinction, and we examine the general challenges in studying extinction in subjects that differ in learning or performance prior to extinction.     

Nucleotide sequence changes between Streptococcus pneumoniae R6 and D39 strains determined by an oligonucleotide hybridization DNA sequencing technology

The Gram-positive pathogen Streptococcus pneumoniae, which can be responsible for serious cases of pneumonia and meningitis, has been intensely studied for almost 100 years. Many of the key experiments have been performed in two strains; the non-pathogenic S. pneumoniae R6 and its pathogenic progenitor, S. pneumoniae D39. Whereas the genomic sequence of the R6 strain has been published, there is relatively little genomic information available on D39. Since R6 was derived from D39, we wished to explore the utility of a new technology, Comparative Genome Sequencing, which uses a set of custom oligonucleotide arrays to compare DNA sequences between similar strains. We report here the nucleotide polymorphisms identified between the R6 strain and D39 based on an R6 sequencing array. During the process, we were also able to confirm all of the high confidence changes reported by the oligonucleotide array chip by sequencing the region in the genome around the changes identified with the genome hybridization chip. We also discuss the potential impact of some of the amino acid changes found between these two widely used strains of pneumococci.     

Differences in DBA/1J and DBA/2J reveal lipid QTL genes

Recent advances in mouse genomics have revealed considerable variation in the form of single-nucleotide polymorphisms (SNPs) among common inbred strains. This has made it possible to characterize closely related strains and to identify genes that differ; such genes may be causal for quantitative phenotypes. The mouse strains DBA/1J and DBA/2J differ by just 5.6% at the SNP level. These strains exhibit differences in a number of metabolic and lipid phenotypes, such as plasma levels of triglycerides (TGs) and HDL. A cross between these strains revealed multiple quantitative trait loci (QTLs) in 294 progeny. We identified significant TG QTLs on chromosomes (Chrs) 1, 2, 3, 4, 8, 9, 10, 11, 12, 13, 14, 16, and 19, and significant HDL QTLs on Chrs 3, 9, and 16. Some QTLs mapped to chromosomes with limited variability between the two strains, thus facilitating the identification of candidate genes. We suggest that Tshr is the QTL gene for Chr 12 TG and HDL levels and that Ihh may account for the TG QTL on Chr 1. This cross highlights the advantage of crossing closely related strains for subsequent identification of QTL genes.     

Genetic analysis of mortality in murine angiostrongyliasis costaricensis using SMXA recombinant inbred mouse strains

The SMXA recombinant inbred mouse strain set was produced by systematic inbreeding from the F2 generation of a cross between two progenitor inbred strains, A/J and SM/J, which differed markedly with respect to the patterns of infection with Angiostrongylus costaricensis. We have applied this set to genetic analysis of mouse susceptibility to this nematode infection. The mortality was variable among substrains of the SMXA RI strains, indicating the involvement of multiple genes. Linkage analysis showed several chromosomal regions closely linked to mortality; chromosome 6 (D6Rik86, 87; P0.001), 10 (D10Rik66–D10Mit12; P=0.0058), 13 (D13Rik79, 80; P=0.0096) and 17 (D17Mit28–D17Rik76; P=0.0088).     

A genome-wide set of congenic mouse strains derived from CAST/Ei on a C57BL/6 background

We previously reported the construction of two sets of heterozygous congenic strains spanning the mouse genome. For both sets, C57BL/6J was employed as the background strain while DNA from either DBA/2 or CAST/Ei was introgressed to form the congenic region. We have subsequently bred most of these strains to produce homozygous breeding stocks. Here, we report the characterization of the strain set based on CAST/Ei. CAST/Ei is the most genetically distant strain within the Mus mus species and many trait variations relevant to common diseases have been identified in CAST/Ei mice. Despite breeding difficulties for some congenic regions, presumably due to incompatible allelic variations between CAST/Ei and C57BL/6, the resulting congenic strains cover about 80% of the autosomal chromosomes and will be useful as a resource for the further analysis of quantitative trait loci between the strains.     

In vitro culture studies of granulocyte/macrophage and erythroid progenitor cells in lymphoproliferative disorders

Granulocyte/macrophage progenitor cells (CFU-GM) and erythroid progenitor cells (BFU-E) have been assayed in peripheral blood (PB) and/or bone marrow (BM) from 12 patients with acute lymphocytic leukemia (ALL), 16 patients with chronic lymphocytic leukemia (CLL) and 31 patients with various forms of non-Hodgkin lymphoma (NHL) without BM involvement. Progenitor cell growth in PB and BM from the NHL patients did not differ statistically from controls (p greater than 0.1). CFU-GM and BFU-E per ml PB were markedly increased in ALL and CLL patients (p less than 0.001) while CFU-GM and BFU-E per plated BM cells from these patients were severely depressed (p less than 0.001). Lymphoblasts from one ALL patient failed to inhibit CFU-GM and BFU-E-derived colony growth from control PB mononuclear cells. The high levels of circulating progenitor cells in ALL and CLL patients clearly distinguish them from other cytopenic hematological malignancies, in which decreased progenitor cell levels have been demonstrated previously (acute myeloid leukemia, hairy cell leukemia). The cause of this finding and its pathophysiological implication still remains to be established.     

Characterization of hyperinsulinemic recombinant inbred (RI) strains (SMXA-5 and SMXA-9) derived from normoinsulinemic SM/J and A/J mice.

We discovered two mouse strains (SMXA-5 and SMXA-9) with hyperinsulinemia among the substrains and progenitor strains (SM/J and A/J) of the SMXA recombinant inbred (RI) strains, and characterized the two strains at 20 weeks of age. SMXA-5 (mean +/- S.E.M: 9.6 +/- 1.7 ng/ml) and SMXA-9 (7.7 +/- 1.3 ng/ml) males had higher serum immunoreactive insulin levels than SM/J (1.4 +/- 0.3 ng/ml) and A/J (1.1 +/- 0.1 ng/ml) males in the nonfasting condition. The hypoglycemic response to insulin at 30 min after injection was significantly less in SMXA-5 males than in SM/J mice. Glucose tolerance test revealed that the incidence of impaired glucose tolerant males was 58% (11/19) in SMXA-5 and 42% (10/24) in SMXA-9 strains, but none in SM/J and A/J strains. SMXA-5 (209 +/- 29 mg/dl) and SMXA-9 (235 +/- 31 mg/dl) had higher serum triglyceride levels than SM/J (126 +/- 14 mg/dl) and A/J (89 +/- 5 mg/dl) males in the nonfasting condition. Histologic examination revealed enlarged islets in the pancreas of hyperinsulinemic SMXA-5 male mice. Moreover, SMXA-5 and SMXA-9 mice exhibited mild obesity. SMXA-5 and SMXA-9 males were therefore characterized by hyperinsulinemia, impaired glucose tolerance, hypertriglyceridemia and mild obesity which resembled some of the phenotypes of human Syndrome X, although both progenitor strains were normal so far as we examined. Since the RI strains are a powerful tool to facilitate polygenic-trait analysis, SMXA-5 and SMXA-9 mice will be useful materials to investigate the genetic basis of complex diseases, and are possible new metabolic models in relation to hyperinsulinemia.     

Nicaraven Attenuates Radiation-Induced Injury in Hematopoietic Stem/Progenitor Cells in Mice

Nicaraven, a chemically synthesized hydroxyl radical-specific scavenger, has been demonstrated to protect against ischemia-reperfusion injury in various organs. We investigated whether nicaraven can attenuate radiation-induced injury in hematopoietic stem/progenitor cells, which is the conmen complication of radiotherapy and one of the major causes of death in sub-acute phase after accidental exposure to high dose radiation. C57BL/6 mice were exposed to 1 Gy γ-ray radiation daily for 5 days in succession (a total of 5 Gy), and given nicaraven or a placebo after each exposure. The mice were sacrificed 2 days after the last radiation treatment, and the protective effects and relevant mechanisms of nicaraven in hematopoietic stem/progenitor cells with radiation-induced damage were investigated by ex vivo examination. We found that post-radiation administration of nicaraven significantly increased the number, improved the colony-forming capacity, and decreased the DNA damage of hematopoietic stem/progenitor cells. The urinary levels of 8-oxo-2′-deoxyguanosine, a marker of DNA oxidation, were significantly lower in mice that were given nicaraven compared with those that received a placebo treatment, although the levels of intracellular and mitochondrial reactive oxygen species in the bone marrow cells did not differ significantly between the two groups. Interestingly, compared with the placebo treatment, the administration of nicaraven significantly decreased the levels of the inflammatory cytokines IL-6 and TNF-α in the plasma of mice. Our data suggest that nicaraven effectively diminished the effects of radiation-induced injury in hematopoietic stem/progenitor cells, which is likely associated with the anti-oxidative and anti-inflammatory properties of this compound.     

A new framework marker-based linkage map and SDPs for the Rat HXB/BXH strain set

A new contiguous genetic linkage map of the HXB/BXH set of rat recombinant inbred (RI) strains was constructed to enhance QTL mapping power and precision, and thereby make the RI strain set a better genomics resource. The HXB/BXH rat RI strains were developed from a cross between the hypertensive SHR/OlaIpcv and normotensive BN-Lx/Cub rat strains and have been shown useful for identifying quantitative trait loci (QTL) for a variety of cardiovascular, metabolic, and behavioral phenotypes. In the current analysis, the DNAs from 31 existing strains, 1 substrain, and 4 extinct strains were genotyped for a selection of polymorphic microsatellite marker loci, predominantly polymorphic framework markers from high-density integrated rat genome maps. The resulting linkage map consists of 245 microsatellite markers spanning a total length of 1789 cM with an average inter-marker distance of ~8.0 cM. This map covers the rat genome contiguously and completely with the exception of two locations on Chromosomes (Chrs) 11 and 16. The new genotypic information obtained also permitted further genetic characterization of the RI strain set including strain independence, genetic similarity among the individual strains, and non-syntenic associations between loci.     

A mouse-based strategy for cyclophosphamide pharmacogenomic discovery.

Genome-wide mapping approaches are needed to more fully understand the genetic basis of chemotherapy response. Because of technical and ethical limitations, cancer pharmacogenomics has not yet benefited from traditional robust familial genetic strategies. We have therefore explored the use of the inbred mouse as a genetic model system in which to study response to the cytotoxic agent cyclophosphamide. Multiple phenotypes have been assessed in response to cyclophosphamide in up to 19 inbred mouse strains, including in vitro hematopoietic progenitor cell toxicity and the mobilization of hematopoietic progenitor cells into peripheral blood. Hematopoietic progenitor cell toxicity in vitro varied 2-fold among strains, whereas in vivo progenitor cell mobilization varied almost 75-fold among strains. Males mobilized more hematopoietic progenitor cells than did females, and the low-mobilization phenotype was dominant to the high-mobilization phenotype in F1 hybrid animals. In an initial attempt to analyze candidate genes, genetic variation was assessed in three cytochrome P-450 genes involved in the metabolism of cyclophosphamide. Resequencing of eight strains identified 26 polymorphisms in these genes that may influence response to cyclophosphamide. Distinct regions of high- and low-polymorphism rates were identified, and two common haplotypes were shared among the strains for each gene that exhibited variation. This phenotypic and genotypic variation among inbred strains provides a framework for cyclophosphamide pharmacogenomic discovery.     

Genetic Variation within and Between Domesticated Chinook Salmon, Oncorhynchus tshawytscha, Strains and their Progenitor Populations

Domesticated chinook salmon strains in British Columbia (BC), Canada are believed to have originated primarily from populations of the Big Qualicum (BQ) River and Robertson Creek (RC) on Vancouver Island in the early 1980s. The number of parental fish that gave rise to the domesticated strains and their subsequent breeding history during approximately five ensuing generations of domestication were not documented. Genetic variation at 13 microsatellite loci was examined in samples from two domesticated strains and the two progenitor populations to determine the genetic relationships among them. The domesticated strains had lower allelic diversity and tended to have lower levels of expected heterozygosity than did the BQ and RC progenitor populations. Only three alleles over all 13 loci were detected in the domesticated strains that were not present in the BQ and RC samples, whereas the progenitor strains possessed over 25 (BQ) and 43 (RC) private alleles. Genetic distance and F_ST values also indicated a closer relationship of the domesticated strains with the BQ than the RC population. One domesticated strain had a significant excess of heterozygosity compared with that expected under conditions of mutation-drift equilibrium, indicative of a recent genetic bottleneck. Genetic differentiation between the domesticated strains was as great as that distinguishing them from the progenitor populations, indicating that the genetic base of domesticated chinook salmon could be increased by hybridization. The existence of genetically distinct domesticated strains of chinook salmon in coastal BC generates the need for an evaluation of potential genetic interactions between domesticated escapees and natural spawning populations.     

Analysis of oocyte quality in recombinant inbred mouse strains developed from KE and CBA strains that differ in fertilization efficiency

Recombinant inbred (RI) mouse strains were developed from reciprocal crosses between two inbred strains differing in the proportion of fertilized ova (CBA, 100%; KE, 77%), to analyse the underlying factors. A correlation (r = 0.83, P < 0.01) between fertilization efficiency within 22 RI strains and after mating RI females with KE males proved that oocyte quality was involved. The following oocyte parameters were analysed in RI and progenitor strains: time of meiotic maturation, rapidity of enzymatic removal of egg investments, and proportion of fertilized ova with supplementary spermatozoa in the perivitelline space. Among the RI strains, high incidence of supplementary spermatozoa was correlated with lower efficiency of fertilization (r = -0.58, P < 0.05) and with slow meiotic maturation (r = -64, P < 0.01), suggesting that delayed maturation may affect oocyte ability of being fertilized by the first penetrating spermatozoon. However, significant correlations were also found between characters which coexist within the progenitor strains, but are not likely to be physiologically related; this suggests that RI strains have inherited large blocks of progenitor genomes, not disrupted by recombination. The strain distribution pattern (SDP) of the analysed traits revealed CBA-like, KE-like, and intermediate phenotypes, indicating that they are polygenically determined. No linkages were found between the studied traits and 12 enzymatic markers. However, the SDP for fertilization efficiency showed a preponderance of non-matching strains (15/19) in relation to agouti locus; the known instability of this chromosome region makes it possible that a putative linkage was disrupted by recombination when RI strains were created.     

A Single Amino Acid Difference Is Sufficient to Elicit Vegetative Incompatibility in the Fungus Podospora Anserina

Vegetative incompatibility is known to limit heterokaryosis in filamentous fungi. It results from genetic differences between incompatible strains at specific loci. The proteins encoded by the two incompatible alleles het-s and het-S of the fungus Podospora anserina differ from each other by 14 amino acids. Two approaches have been used to identify how many and which of these differences are necessary to elicit incompatibility. Twelve alleles of the het-s locus of wild-type isolates of P. anserina and of the related species Podospora comata have been sequenced to determine the extent of the variability of genes controlling s and S specificities. Expression of hybrid het-s/het-S genes and site-specific mutagenesis revealed that the specificities of het-s and het-S are under the control of a limited number of amino acid differences. The results show that vegetative incompatibility between s and S strains can be attributed to a single amino acid difference in the proteins encoded by the het-s locus.     

BALB/c和C_(57)BL/6小鼠在基因功能检测中行为学的比较研究

目的　探索BALB c和C57BL 6两个品系在有关实验中的不同作用。方法　选取了结合随机测序与生物信息学分析设计合成的神经系统表达的一些基因的反义核酸 (anti sense)中的 2个 ,用Hamilton微量注射器将其分别定量注射到BALB c和C57BL 6小鼠的侧脑室 ,并分别设注射生理盐水和随机序列核酸 (Scramble)的对照组。每一反义核酸实验组和对照组各注射 1 0只小鼠 ,之后观察实验组与对照组在不同行为学实验中的差异。小鼠的行为学检测模型为 :考察日常代谢能力的摄食量 ,考察Locomotionactivity(移动 )的旷场行为 ,考察疼痛阈值的甩尾试验和考察记忆能力的步下法实验。结果　注射No 1基因的反义核酸后 ,两品系的实验组均在测试记忆力的步下法 (Step -downTest)试验中表现出记忆力减弱 ,且与对照组差异明显 ,说明No 1基因的功能确与记忆相关。注射No 2基因的反义核酸后 ,在测试移动能力的旷场行为 (OpenFieldBehavior)试验中 ,BALB c实验组跨格、直立行为均比对照组明显减少 ,说明受此反义核酸影响显著 ,而C57BL 6实验组则与对照组无大的差异。此外 ,在生理盐水对照组和随机序列核酸对照组的实验中以及其他行为学模型的实验中 ,两品系也存在着一定的差异。结论　用遗传背景不同的多品系进行相关实验 ,可进一步建立     

BIOCHEMICAL, PHYSIOLOGICAL, AND MOLECULAR ANALYSIS OF SEXUAL ISOLATION IN THE SPECIES COMPLEX CLOSTERIUM PERACEROSUM-STRIGOSUM-LITTORALE (CHLOROPHYTA)1

Closterium strains obtained from Japan ( NIES-64 and -65 ) and Nepal ( NIES-67 and -68 ) have been classified as the same taxonomic species; however, they are sexually isolated from each other. When NIES-64 and -65 cells were separately incubated in a medium in which both strains had previously been cultured together, release of protoplasts from both strains was observed. We suggest that factors responsible for the release of protoplasts from cells of both NIES-64 and -65 are produced in a mixed culture of these cells and function during conjugation. These factors, however, had no effect on the release of protoplasts from cells of strains NIFS-67 or -68. Alternatively, a protein that is responsible for the release of protoplasts from cells of NIES-68, called the protoplast-release-inducing protein ( PR-IP ), had no effect on the release of protoplasts from cells of strains NIES-64 or -65. When the media obtained from the culture of NIES-64 and -65 cells at various mixing ratios were analyzed by western blotting with antiserum to a 42-kDa subunit of PR-IP, no cross reaction was detected. In Southern hybridization analysis, no hybridizing band was observed when genomic DNAs of NIES-64 and -65 cells were probed with cDNAs encoding the two subunits of PR-IP. We suggest from these results that the factors responsible for the release of protoplasts from NIES-64 and -65 cells are not structurally similar to PR-IP. It is known that the release of PR-IP from NIES-67 cells can be induced by the action of another sex pheromone ( PR-IP inducer ) which is released by NIES-68 cells. In contrast, no protoplast-release-inducing activity was observed from either NIES-64 or -65 in a culture medium conditioned by opposite strains. We suggest that the conjugation systems employed by strains NIES-64/ NIES-65 and strains NIES-67 /NIES-68 differ, and we propose a possible mechanism of sexual isolation between these biological species .     

The response of recombinant inbred strains of mice to bacterial lipopolysaccharides.

Fourteen recombinant inbred strains of mice have been produced by the inbreeding of the F2 generation of a cross between C57BL/6J and C3H/HeJ progenitor mice. The responses of these BXH strains to bacterial lipopolysaccharides (LPS) have been characterized. Four BXH strains are high LPS responders and nine strains are low LPS responders. One BXH strain shows intermediate responsiveness which may reflect residual heterozygosity. F1 hybrid mice from low x high responder strains were intermediate in their response to LPS suggesting additive genetic control. The LPS responses in backcross mice from the F1 x low LPS responders showed segregation consistent with LPS responsiveness being determined by a single gene. In 13/14 BXH strains, there was concordant inheritance of LPS responsiveness and the major urinary protein locus Mup-1b. The association of the expression of the Mup-1 alleles with LPS responsiveness in the BXH strains suggests that the defective LPS response gene in C3H/HeJ mice is located on chromosome 4.