Genetic dissection of susceptibility to radiation-induced apoptosis of thymocytes and mapping of Rapop1, a novel susceptibility gene

Genetic dissection of susceptibility to radiation-induced apoptosis of thymocytes was performed by counting dead cells in histologically processed thymuses after 0.5 Gy of whole-body X-irradiation, using recombinant congenic (CcS/Dem) strains derived from inbred mouse strains BALB/cHeA (susceptible) and STS/A (resistant). A high (8/20) number of strains with lower dead cell scores than BALB/cHeA among CcS/ Dem recombinant congenic strains (RCS), which contain 12.5% of STS/A genome in the genetic background of BALB/cHeA strain, indicates that the difference between BALB/cHeA and STS/A is caused by several genes and that susceptibility probably requires BALB/ cHeA alleles at more than one locus. Similar results were obtained with CXS/Hg recombinant inbred (CXS/ Hg) strains. Analysis of F₂ hybrids between BALB/ cHeA and CcS-7, one of the CcS/Dem strains that showed lower dead cell scores than BALB/cHeA, demonstrated that a novel gene (Rapop1, radiation-induced apoptosis 1) controlling susceptibility to radiation-induced apoptosis in the thymus is located in the proximal region of mouse chromosome 16.     

Genetics of susceptibility to radiation-induced apoptosis in colon: two loci on Chromosomes 9 and 16

Apoptosis, a mechanism for removal of genetically damaged cells and for maintenance of desired size of cell populations, has been implicated in tumor development. Previously, we defined polymorphic loci for susceptibility to apoptosis of thymocytes Rapop1, Rapop2, and Rapop3 on mouse Chromosomes 16, 9, and 3, respectively, using recombinant congenic CcS/Dem strains, each of which contains a random set of 12.5% STS/A genome in the genetic background of BALB/cHeA. The STS/A alleles at these loci confer lower susceptibility to radiation-induced apoptosis of thymocytes than the BALB/cHeA. In the present study, we tested susceptibility of colon crypt cells to radiation-induced apoptosis. In contrast to apoptosis in thymus, the STS/A mice were more susceptible to apoptosis in colon than the BALB/cHeA. Among the CcS/Dem strains, CcS-4, CcS-7, and CcS-16 were more susceptible to apoptosis in colon than the BALB/cHeA; in thymus, the CcS-7 mice are less susceptible, and the CcS-4 and CcS-16 are not different from the BALB/cHeA. Thus, individual CcS/Dem strains showed different apoptosis susceptibility in the two organs. Analysis of (CcS-7 × BALB/cHeA)F₂ hybrids revealed linkage of susceptibility to radiation-induced apoptosis of colon crypt cells to two loci on Chrs 9 and 16, to which Rapop2 and Rapop1 are mapped. The STS/A allele at the locus on chromosome 9 results in high susceptibility to apoptosis of colon crypt cells in mice homozygous for the BALB/cHeA allele at the locus on Chr 16. Although these two loci may be identical to Rapop1 and Rapop2, they affect apoptosis in colon in a way different from that in thymus. Received: 9 October 1997 / Accepted: 29 December 1997     

The production of two Th2 cytokines, interleukin-4 and interleukin-10, is controlled independently by locus Cypr1 and by loci Cypr2 and Cypr3, respectively

 The strains BALB/cHeA (BALB/c) and STS/A (STS) differ in production of IL-4 and IL-10, two Th2 cytokines, after stimulation of spleen cells with Concanavalin A, STS being a low and BALB/c a high producer. We analyzed the genetic basis of this strain difference using the recombinant congenic (RC) strains of the BALB/c-c-STS/Dem (CcS/Dem) series. This series comprises 20 homozygous strains. Each CcS/Dem strain contains a different, random set of approximately 12.5% genes of the "donor" strain STS and approximately 87.5% of the "background" strain BALB/c. We selected for further analysis the RC strain production intermediate between BALB/c and STS. In (CcS-20×BALB/c)F₂ hybrids we found that different loci control expression of IL-4 and IL-10. Cypr1 (cytokine production 1) on chromosome 16 near D16Mit15 controls IL-4 production, whereas the production of IL-10 is influenced by loci Cypr2 near D1Mit14 and D1Mit227 on chromosome 1 and Cypr3 marked by D5Mit20 on chromosome 5. In addition, the relationship between the level of these two cytokines depends on the genotype of the F₂ hybrids at a locus cora1 (correlation 1) on chromosome 5. This differential genetic regulation may be relevant for the understanding of biological effects of T-helper cells in mice of different genotypes. Received: 2 March 1998 / Revised: 8 June 1998     

Genetic control of resistance to Trypanosoma brucei brucei infection in mice

Background

Trypanosoma brucei brucei infects livestock, with severe effects in horses and dogs. Mouse strains differ greatly in susceptibility to this parasite. However, no genes controlling these differences were mapped.

Methods

We studied the genetic control of survival after T. b. brucei infection using recombinant congenic (RC) strains, which have a high mapping power. Each RC strain of BALB/c-c-STS/A (CcS/Dem) series contains a different random subset of 12.5% genes from the parental “donor” strain STS/A and 87.5% genes from the “background” strain BALB/c. Although BALB/c and STS/A mice are similarly susceptible to T. b. brucei, the RC strain CcS-11 is more susceptible than either of them. We analyzed genetics of survival in T. b. brucei-infected F₂ hybrids between BALB/c and CcS-11. CcS-11 strain carries STS-derived segments on eight chromosomes. They were genotyped in the F₂ hybrid mice and their linkage with survival was tested by analysis of variance.

Results

We mapped four Tbbr (Trypanosoma brucei brucei response) loci that influence survival after T. b. brucei infection. Tbbr1 (chromosome 3) and Tbbr2 (chromosome 12) have effects on survival independent of inter-genic interactions (main effects). Tbbr3 (chromosome 7) influences survival in interaction with Tbbr4 (chromosome 19). Tbbr2 is located on a segment 2.15 Mb short that contains only 26 genes.

Conclusion

This study presents the first identification of chromosomal loci controlling susceptibility to T. b. brucei infection. While mapping in F₂ hybrids of inbred strains usually has a precision of 40–80 Mb, in RC strains we mapped Tbbr2 to a 2.15 Mb segment containing only 26 genes, which will enable an effective search for the candidate gene. Definition of susceptibility genes will improve the understanding of pathways and genetic diversity underlying the disease and may result in new strategies to overcome the active subversion of the immune system by T. b. brucei.     

The recombinant congenic strains—a novel genetic tool applied to the study of colon tumor development in the mouse

The development of tumors in mice is under multigenic control, but, in spite of considerable efforts, the identification of the genes involved has so far been unsuccessful, because of the insufficient resolution power of the available genetic tools. Therefore, a novel genetic tool, the RC (Recombinant Congenic) strains system, was designed. In this system, a series of RC strains is produced from two inbred strains, a background strain and a donor strain. Each RC strain contains a different small subset of genes from the donor strain and the majority of genes from the background strain. As a consequence, the individual genes of the donor strain which are involved in the genetic control of a multigenic trait, become separated into different RC strains, where they can be identified and studied individually. One of the RC strains series which we produced is made from the parental strains BALB/cHeA (background strain) and STS/A (donor strain). We describe the genetic composition of this BALB/cHeA-C-STS/A (CcS/Dem) series and show, using 45 genetic autosomal markers, that it does not deviate from the theoretical expectation. We studied the usefulness of the CcS/Dem RC strains for analysis of the genetics of colon tumor development. The two parental strains, BALB/cHeA and STS/A, are relatively resistant and highly susceptible, respectively, to the induction of colon tumors by 1,2-dimethylhydrazine (DMH). The individual RC strains differ widely in colon tumor development after DMH treatment; some are highly susceptible, while others are very resistant. This indicates that a limited number of genes with a major effect are responsible for the high susceptibility of the STS strain. Consequently, these genes can be mapped by further analysis of the susceptible RC strains. The differences between the RC strains were not limited to the number of tumors, but the RC strains differed also in size of the tumors and the relative susceptibility of the two sexes. Our data indicate that the number of tumors and the size of tumors are not controlled by the same genes. The genetics of these different aspects of colon tumorigenesis can also be studied by the RC strains. The DMH-treated mice of the parental strains and the RC strains also developed anal tumors and haemangiomas in varying numbers. The strain distribution pattern (SDP) of susceptibility for each of the three types of tumors induced by DMH is different, indicating that development of these tumors is under control of different, largely non-overlapping, sets of genes. Thus, with a single series of RC strains, genes involved in tumorigenesis in various organs and tissues can be studied separately. These results indicate that the novel genetic tool, the RC strain system, offers new possibilities for analysis of the multigenic control of tumor development.     

Separation of multiple genes controlling the T-cell proliferative response to IL-2 and anti-CD3 using recombinant congenic strains

T lymphocytes of the strain BALB/cHeA exhibit a low proliferative response to IL-2 and a high response to the anti-CD3 monoclonal antibodies, while the strain STS/A lymphocyte response to these stimuli is the opposite. We analyzed the genetic basis of this strain difference, using a novel genetic tool: the recombinant congenic strains (RCS). Twenty BALB/c-c-STS/Dem (CcS/Dem) RCS were used, each containing a different random set of approximately 12.5% of the genes from STS and the remainder from BALB/c. Consequently, the genes participating in the multigenic control of a phenotypic difference between BALB/c and STS become separated into different CcS strains where they can be studied individually. The strain distribution patterns of the proliferative responses to IL-2 and anti-CD3 in the CcS strains are different, showing that different genes are involved. The large differences between individual CcS strains in response to IL-2 or anti-CD3 indicate that both reactions are controlled by a limited number of genes with a relatively large effect. The high proliferative response to IL-2 is a dominant characteristic. It is not caused by a larger major cell subset size, nor by a higher level of IL-2R expression. The response to anti-CD3 is known to be controlled by polymorphism in Fc receptor 2 (Fcgr2) and the CcS strains carrying the low responder Fcgr2 allele indeed responded weakly. However, as these strains do respond to immobilized anti-CD3, while the STS strain does not, and as some CcS strains with the BALB/c allele of Fcgr2 are also low responders, additional gene(s) of the STS strain strongly depress the anti-CD3 response. In a backcross between the high responder and the low responder strains CcS-9 and CcS-11, one of these unknown genes was mapped to the chromosome 10 near D10Mit14. The CcS mouse strains which carry the STS alleles of genes controlling the proliferative response to IL-2 and anti-CD3 allow the future mapping, cloning, and functional analysis of these genes and the study of their biological effects in vivo.     

T-cell proliferative response is controlled by loci Tria4 and Tria5 on mouse Chromosomes 7 and 9

Lymphocytes of mouse strains BALB/cHeA (BALB/c) and STS/A (STS) differ in their response to CD3 antibody (anti-CD3). We analyzed the genetic basis of this strain difference, using the Recombinant Congenic Strains (RCS) of the BALB/c-c-STS/Dem (CcS/Dem) series. Each of the 20 CcS/Dem strains carries a different, random combination of 12.5% genes from the nonresponding strain STS and 87.5% genes of the intermediate responder strain BALB/c. Differences in the magnitude of anti-CD3-induced response among CcS/Dem strains indicated that in addition to Fcγ receptor 2 (Fcgr2) other genes are involved in the control of this response as well, and we have already mapped loci Tria1 (T cell receptor-induced activation 1), Tria2, and Tria3. In order to map additional Tria genes, we tested F₂ hybrids between the high responder RC strain CcS-9 and the low responder strain CcS-11. Proliferation in complete RPMI medium without anti-CD3 is controlled by locus Sprol1 (spontaneous proliferation 1) linked to the marker D4Mit23 on Chr 4. At concentration 0.375 μg/ml anti-CD3 mAb, the response was controlled by a locus Tria4, which maps to the marker D7Mit32 on Chr 7. The response to the higher concentration of mAb, 3 μg/ml, was controlled by Tria5, which mapped to the marker D9Mit15 on Chr 9. Anti-CD3 is being used for modulation of lymphocyte functions in transplantation reactions and in cancer treatment. Study of mechanisms of action of different Tria loci could lead to better understanding of genetic regulation of these reactions. Received: 28 October 1998 / Accepted: 17 March 1999     

Most lung and colon cancer susceptibility genes are pair-wise linked in mice, humans and rats

Genetic predisposition controlled by susceptibility quantitative trait loci (QTLs) contributes to a large proportion of common cancers. Studies of genetics of cancer susceptibility, however, did not address systematically the relationship between susceptibility to cancers in different organs. We present five sets of data on genetic architecture of colon and lung cancer susceptibility in mice, humans and rats. They collectively show that the majority of genes for colon and lung cancer susceptibility are linked pair-wise and are likely identical or related. Four CcS/Dem recombinant congenic strains, each differing from strain BALB/cHeA by a different small random subset of ±12.5% of genes received from strain STS/A, suggestively show either extreme susceptibility or extreme resistance for both colon and lung tumors, which is unlikely if the two tumors were controlled by independent susceptibility genes. Indeed, susceptibility to lung cancer (Sluc) loci underlying the extreme susceptibility or resistance of such CcS/Dem strains, mapped in 226 (CcS-10 x CcS-19)F2 mice, co-localize with susceptibility to colon cancer (Scc) loci. Analysis of additional Sluc loci that were mapped in OcB/Dem strains and Scc loci in CcS/Dem strains, respectively, shows their widespread pair-wise co-localization (P = 0.0036). Finally, the majority of published human and rat colon cancer susceptibility genes map to chromosomal regions homologous to mouse Sluc loci. 12/12 mouse Scc loci, 9/11 human and 5/7 rat colon cancer susceptibility loci are close to a Sluc locus or its homologous site, forming 21 clusters of lung and colon cancer susceptibility genes from one, two or three species. Our data shows that cancer susceptibility QTLs can have much broader biological effects than presently appreciated. It also demonstrates the power of mouse genetics to predict human susceptibility genes. Comparison of molecular mechanisms of susceptibility genes that are organ-specific and those with trans-organ effects can provide a new dimension in understanding individual cancer susceptibility.     

Gene-specific sex effects on eosinophil infiltration in leishmaniasis

Background

Sex influences susceptibility to many infectious diseases, including some manifestations of leishmaniasis. The disease is caused by parasites that enter to the skin and can spread to the lymph nodes, spleen, liver, bone marrow, and sometimes lungs. Parasites induce host defenses including cell infiltration, leading to protective or ineffective inflammation. These responses are often influenced by host genotype and sex. We analyzed the role of sex in the impact of specific gene loci on eosinophil infiltration and its functional relevance.

Methods

We studied the genetic control of infiltration of eosinophils into the inguinal lymph nodes after 8 weeks of Leishmania major infection using mouse strains BALB/c, STS, and recombinant congenic strains CcS-1,-3,-4,-5,-7,-9,-11,-12,-15,-16,-18, and -20, each of which contains a different random set of 12.5% genes from the parental “donor” strain STS and 87.5% genes from the “background” strain BALB/c. Numbers of eosinophils were counted in hematoxylin-eosin-stained sections of the inguinal lymph nodes under a light microscope. Parasite load was determined using PCR-ELISA.

Results

The lymph nodes of resistant STS and susceptible BALB/c mice contained very low and intermediate numbers of eosinophils, respectively. Unexpectedly, eosinophil infiltration in strain CcS-9 exceeded that in BALB/c and STS and was higher in males than in females. We searched for genes controlling high eosinophil infiltration in CcS-9 mice by linkage analysis in F₂ hybrids between BALB/c and CcS-9 and detected four loci controlling eosinophil numbers. Lmr14 (chromosome 2) and Lmr25 (chromosome 5) operate independently from other genes (main effects). Lmr14 functions only in males, the effect of Lmr25 is sex independent. Lmr15 (chromosome 11) and Lmr26 (chromosome 9) operate in cooperation (non-additive interaction) with each other. This interaction was significant in males only, but sex-marker interaction was not significant. Eosinophil infiltration was positively correlated with parasite load in lymph nodes of F₂ hybrids in males, but not in females.

Conclusions

We demonstrated a strong influence of sex on numbers of eosinophils in the lymph nodes after L. major infection and present the first identification of sex-dependent autosomal loci controlling eosinophilic infiltration. The positive correlation between eosinophil infiltration and parasite load in males suggests that this sex-dependent eosinophilic infiltration reflects ineffective inflammation.

     

Mouse genetic model for clinical and immunological heterogeneity of leishmaniasis

Systematic assessment of the role of host genes in clinico-pathological and immunological manifestations of Leishmania major-induced disease in mice was performed using 20 recombinant congenic (RC) strains. As the RC strains are homozygous and each carries a different, random set of 12.5% genes from the resistant strain, STS/A, and 87.5% genes from the susceptible strain, BALB/cHeA, they allowed us to study the pathological and immunological characteristics of infected hosts in 20 fixed different random combinations of BALB/c and STS genes. The 20 RC strains differ widely in expression of different symptoms of disease and in immunological characteristics. Disease or healing in different strains occurred in association with different components of immune response -- with the exception of a frequently occurring correlation between the disease and IgE levels. Moreover, some parameters of the immune response were highly correlated in some strains but not at all in others. This shows that several patterns of the immune response may be associated with the same clinical outcome, depending on the host genotype. Our data also suggest that despite the complexity of regulation, when a sufficient number of controlling loci is known, the prediction of a phenotype is possible. Combining functional and clinical information with multilocus genotyping may improve our ability to predict the progression of the disease and to optimize the treatment.     

Variations in genetic control of susceptibility to Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease. I. Differences between susceptible SJL/J and resistant BALB/c strains map near the T cell beta-chain constant gene on chromosome 6

In some susceptible mouse strains, intracerebral (IC) inoculation of Theiler's murine encephalomyelitis virus (TMEV) results in a persistent infection leading to chronic demyelinating disease. Previous genetic analyses between susceptible SJL/J and resistant C57BL/6 mice indicated a role for multiple unlinked genes in the development of clinical and histopathological disease, including a major influence of the D region of the H-2 complex. In this study, genetic analysis of a different strain combination (susceptible SJL/J and resistant BALB/c) also demonstrates the involvement of multiple genes, but the H-2 genotype (H-2s and H-2d, respectively) does not appear to contribute significantly to susceptibility differences. In both segregation studies and recombinant-inbred (R-I) analysis, clinical and histopathological disease occurs in both H-2s homozygotes and H-2d homozygotes (as well as H-2s/H-2d heterozygotes), with the actual frequency related to the proportion of non-H-2 genome from the susceptible strain. There appear to be at least two non-H-2 genes involved in differential susceptibility of SJL/J and BALB/c to TMEV-induced disease. Analysis of R-I strains generated from BALB/c and SJL/J progenitors indicates linkage of at least one of these non-H-2 genes to those encoding the constant portion of the beta-chain of the T cell receptor on chromosome 6. Many genes may actually be involved, but each strain comparison defines a different subset of these loci--only those at which the two strains in question carry "functionally" different alleles. Thus, different strain comparisons may accent the roles of different genes in resistance to the same infectious organism or disease process. In addition to the genes identified thus far, there may be yet other genes contributing to development of TMEV-induced disease, but their recognition may require analysis of still other strain combinations.     

Spink2 Modulates Apoptotic Susceptibility and Is a Candidate Gene in the Rgcs1 QTL That Affects Retinal Ganglion Cell Death after Optic Nerve Damage

The Rgcs1 quantitative trait locus, on mouse chromosome 5, influences susceptibility of retinal ganglion cells to acute damage of the optic nerve. Normally resistant mice (DBA/2J) congenic for the susceptible allele from BALB/cByJ mice exhibit susceptibility to ganglion cells, not only in acute optic nerve crush, but also to chronic inherited glaucoma that is characteristic of the DBA/2J strain as they age. SNP mapping of this QTL has narrowed the region of interest to 1 Mb. In this region, a single gene (Spink2) is the most likely candidate for this effect. Spink2 is expressed in retinal ganglion cells and is increased after optic nerve damage. This gene is also polymorphic between resistant and susceptible strains, containing a single conserved amino acid change (threonine to serine) and a 220 bp deletion in intron 1 that may quantitatively alter endogenous expression levels between strains. Overexpression of the different variants of Spink2 in D407 tissue culture cells also increases their susceptibility to the apoptosis-inducing agent staurosporine in a manner consistent with the differential susceptibility between the DBA/2J and BALB/cByJ strains.     

Genetics of host response to Leishmania tropica in mice - different control of skin pathology, chemokine reaction, and invasion into spleen and liver

Background

Leishmaniasis is a disease caused by protozoan parasites of genus Leishmania. The frequent involvement of Leishmania tropica in human leishmaniasis has been recognized only recently. Similarly as L. major, L. tropica causes cutaneous leishmaniasis in humans, but can also visceralize and cause systemic illness. The relationship between the host genotype and disease manifestations is poorly understood because there were no suitable animal models.

Methods

We studied susceptibility to L. tropica, using BALB/c-c-STS/A (CcS/Dem) recombinant congenic (RC) strains, which differ greatly in susceptibility to L. major. Mice were infected with L. tropica and skin lesions, cytokine and chemokine levels in serum, and parasite numbers in organs were measured.

Principal Findings

Females of BALB/c and several RC strains developed skin lesions. In some strains parasites visceralized and were detected in spleen and liver. Importantly, the strain distribution pattern of symptoms caused by L. tropica was different from that observed after L. major infection. Moreover, sex differently influenced infection with L. tropica and L. major. L. major-infected males exhibited either higher or similar skin pathology as females, whereas L. tropica-infected females were more susceptible than males. The majority of L. tropica-infected strains exhibited increased levels of chemokines CCL2, CCL3 and CCL5. CcS-16 females, which developed the largest lesions, exhibited a unique systemic chemokine reaction, characterized by additional transient early peaks of CCL3 and CCL5, which were not present in CcS-16 males nor in any other strain.

Conclusion

Comparison of L. tropica and L. major infections indicates that the strain patterns of response are species-specific, with different sex effects and largely different host susceptibility genes.     

Regulation of resistance to leprosy by chromosome 1 locus in the mouse

Mice of different inbred strains vary in their resistance to intravenous infection with Mycobacterium lepraemurium (MLM). The mean survival time of MLM-infected A/J and DBA/2 mice is significantly longer than that of similarly infected C57BL/6 and BALB/c mice. The typing of AXB/BXA recombinant inbred strains (A = A/J, B = C57BL/6) for the trait of relative resistance/susceptibility to MLM revealed a perfect match with the strain distribution pattern of resistance/susceptibility to Mycobacterium bovis (BCG), the trait which is controlled by the Bcg (Ity, Lsh) locus on chromosome 1. The control, by this gene, of response to MLM was further confirmed by the demonstration that BALB/c-Bcg ^r congenic mice,which carry the DBA/2-derived Bcg ^r (resistant) allele on chromosome 1, are significantly more resistant to MLM infection than their BALB/c (Bcg ^s , susceptible) counterparts.     

Pas1 is a common lung cancer susceptibility locus in three mouse strains

Inherited predisposition to lung cancer is a phenotypic trait shared by different mouse inbred strains that show either a high or an intermediate predisposition. Other strains are instead genetically resistant. The Pas1 locus is the major determinant of lung cancer predisposition in the A/J strain (Gariboldi et al. 1993). To define the determinants of susceptibility to lung tumorigenesis in the highly susceptible SWR/J and in the intermediately susceptible BALB/c mice, we analyzed (BALB/c × SWR/J)F₂ and (BALB/c × C3H/He)F₂ crosses by genetic linkage experiments. The present results provide unequivocal evidence that the same Pas1/+ allele that leads to lung cancer predisposition is shared by A/J, SWR/J, and BALB/c strains. The intermediate susceptibility of the BALB/c strain would result by interaction of Pas1 locus with lung cancer resistance loci. Received: 18 April 1997 / Accepted: 15 June 1997     

Analysis of candidate genes included in the mammary cancer susceptibility 1 (Mcs1) region

The rat strain COP is resistant to spontaneous and carcinogen-induced mammary cancer, whereas the strain WF is susceptible. Using genetic linkage analysis of (WF × COP) F₁× WF backcrosses, LC Hsu, LA Shepel and co-workers showed that a region at the centromeric end of Chromosome (Chr) 2 (2q1) segregates with the sensitivity to mammary cancer development. The responsible locus was named Mcs1 (for mammary cancer susceptibility 1). We have developed the chromosome map of the 2q1 region by localizing 18 genes, 4 ESTs, and several anonymous markers, using radiation hybrids and fluorescence in situ hybridization. The region containing Mcs1 was delineated to 2q12–q14. Five of the genes (Mef2c, Map1b, Ccnh, Rasa, Rasgrf2) were assigned to this region and were shown to be expressed in the rat mammary glands, while three possible functional candidate genes, Pi3kr1, Rad17, and Naip, were excluded from the critical region. Since cyclin H, encoded by Ccnh, plays an important role in the control of the cell cycle and since the proteins encoded by Rasa and Rasgrf2 control the activity of the RAS oncoprotein, the corresponding genes appeared as both functional and positional Mcs1 candidates. RT-PCR experiments on RNA extracted from mammary glands of the two rat strains (COP, WF) was done. No amino acid sequence difference was found between the two strains. These results argue against the hypothesis that any of these three genes is Mcs1. Received: 25 September 2000 / Accepted: 15 November 2000     

Dlx2 (Tes1), a homeobox gene of the Distal-less family, assigned to conserved regions on human and mouse chromosomes 2

Dlx-2 (also called Tes-1), a mammalian member of the Distal-less family of homeobox genes, is expressed during murine fetal development in spatially restricted domains of the forebrain. Searching for a candidate neurological mutation that might involve this gene, we have assigned the human and mouse loci to regions of conserved synteny on human chromosome 2, region cen-q33, and mouse chromosome 2 by Southern analysis of somatic cell hybrid lines. An EcoRI dimorphism, discovered in common inbred laboratory strains, was used for recombinant inbred strain mapping. The results place Dlx-2/Tes-1 near the Hox-4 cluster on mouse chromosome 2.     

Chromosomal Mapping ofTmp(Emp1),Xmp(Emp2), andYmp(Emp3), Genes Encoding Membrane Proteins Related toPmp22

We have recently characterized a novel mammalian gene family, encoding membrane glycoproteins with four trans-membrane domains. This gene family includes the previously studiedPMP22,which is involved in the Charcot–Marie–Tooth neuropathy, and three novel genes:TMP, XMP,andYMP(HGMW-approved symbolsEMP1, EMP2andEMP3,respectively). TheTmp(tumor-associated membrane protein) gene was isolated from a c-mycinduced mouse brain tumor and is expressed in several highly proliferative cell types. We have now isolated cDNAs of the mouseXmpandYmpgenes and determined the chromosomal localization of mouseTmp, Xmp,andYmp. Tmpwas mapped to mouse chromosome 6,Xmpwas mapped to chromosome 16, andYmpwas mapped to chromosome 7.TmpandYmpmap to paralogous chromosomal regions, whereasXmpmaps to a chromosomal region that is putatively paralogous to a region on chromosome 11, to whichPmp22was previously mapped. These data suggest that this family of membrane glycoproteins evolved as a result of chromosomal duplications.     

Mapping the Genes for Susceptibility and Response to Leishmania tropica in Mouse

Background

L. tropica can cause both cutaneous and visceral leishmaniasis in humans. Although the L. tropica-induced cutaneous disease has been long known, its potential to visceralize in humans was recognized only recently. As nothing is known about the genetics of host responses to this infection and their clinical impact, we developed an informative animal model. We described previously that the recombinant congenic strain CcS-16 carrying 12.5% genes from the resistant parental strain STS/A and 87.5% genes from the susceptible strain BALB/c is more susceptible to L. tropica than BALB/c. We used these strains to map and functionally characterize the gene-loci regulating the immune responses and pathology.

Methods

We analyzed genetics of response to L. tropica in infected F₂ hybrids between BALB/c×CcS-16. CcS-16 strain carries STS-derived segments on nine chromosomes. We genotyped these segments in the F₂ hybrid mice and tested their linkage with pathological changes and systemic immune responses.

Principal Findings

We mapped 8 Ltr (Leishmania tropica response) loci. Four loci (Ltr2, Ltr3, Ltr6 and Ltr8) exhibit independent responses to L. tropica, while Ltr1, Ltr4, Ltr5 and Ltr7 were detected only in gene-gene interactions with other Ltr loci. Ltr3 exhibits the recently discovered phenomenon of transgenerational parental effect on parasite numbers in spleen. The most precise mapping (4.07 Mb) was achieved for Ltr1 (chr.2), which controls parasite numbers in lymph nodes. Five Ltr loci co-localize with loci controlling susceptibility to L. major, three are likely L. tropica specific. Individual Ltr loci affect different subsets of responses, exhibit organ specific effects and a separate control of parasite load and organ pathology.

Conclusion

We present the first identification of genetic loci controlling susceptibility to L. tropica. The different combinations of alleles controlling various symptoms of the disease likely co-determine different manifestations of disease induced by the same pathogen in individual mice.