Congenic mapping of the insulin-dependent diabetes (Idd) gene, Idd10, localizes two genes mediating the Idd10 effect and eliminates the candidate Fcgr1

The development of autoimmune diabetes in the nonobese diabetic (NOD) mouse is under the control of multiple insulin-dependent diabetes (Idd) genes. The Idd3 gene, originally defined as a broad peak of linkage on mouse chromosome 3, was subsequently identified as two genes, Idd3 and Idd10, separated by at least 20 cM. The resistance alleles of Idd3 and Idd10 individually confer only partial protection from diabetes but, in combination, result in profound resistance to disease due to an epistatic genetic interaction. In this study, we used newly developed congenic strains to further localize Idd10. Surprisingly, we found that Idd10 itself comprises at least two linked loci: Idd10 and the newly designated Idd17. Idd17 was localized to a 1.1-cM region between D3Mit26 and D3Mit40, proximal to Fcgr1, a candidate gene encoding the high affinity Fc receptor for IgG. Idd10 was localized to a 10-cM region between D3Mit213 and D3Mit106, distal to Fcgr1. Thus, Fcgr1 was excluded as a candidate for either Idd10 or Idd17, despite the fact that the NOD strain expresses a mutant form of the receptor. Interestingly, although Idd10 and Idd17 participate in a genetic interaction with each other, Idd10 but not Idd17 participates in the genetic interaction with Idd3. Our study on chromosome 3 begins to reveal the extent of the polygenic nature of autoimmune diabetes, and demonstrates that the use of congenic strains is an effective mapping strategy, even in the dissection of multiple, linked genes with subtle effects.

Congenic mapping of the insulin-dependent diabetes (Idd) gene, Idd10, localizes two genes mediating the Idd10 effect and eliminates the candidate Fcgr1

The development of autoimmune diabetes in the nonobese diabetic (NOD) mouse is under the control of multiple insulin-dependent diabetes (Idd) genes. The Idd3 gene, originally defined as a broad peak of linkage on mouse chromosome 3, was subsequently identified as two genes, Idd3 and Idd10, separated by at least 20 cM. The resistance alleles of Idd3 and Idd10 individually confer only partial protection from diabetes but, in combination, result in profound resistance to disease due to an epistatic genetic interaction. In this study, we used newly developed congenic strains to further localize Idd10. Surprisingly, we found that Idd10 itself comprises at least two linked loci: Idd10 and the newly designated Idd17. Idd17 was localized to a 1.1-cM region between D3Mit26 and D3Mit40, proximal to Fcgr1, a candidate gene encoding the high affinity Fc receptor for IgG. Idd10 was localized to a 10-cM region between D3Mit213 and D3Mit106, distal to Fcgr1. Thus, Fcgr1 was excluded as a candidate for either Idd10 or Idd17, despite the fact that the NOD strain expresses a mutant form of the receptor. Interestingly, although Idd10 and Idd17 participate in a genetic interaction with each other, Idd10 but not Idd17 participates in the genetic interaction with Idd3. Our study on chromosome 3 begins to reveal the extent of the polygenic nature of autoimmune diabetes, and demonstrates that the use of congenic strains is an effective mapping strategy, even in the dissection of multiple, linked genes with subtle effects.

A 2-Mb YAC contig and physical map of the natural killer gene complex on mouse chromosome 6

We have constructed a physical map of a > 2-Mb region on mouse chromosome 6 that contains the natural killer gene complex (NKC). The map comprises a contig of 14 overlapping yeast artificial chromosomes onto which we positioned 25 NKC markers. NKC genetically linked genes encode > 17 proteins that directly control innate NK cell-mediated tumor lysis and disease resistance. Herein we show that Nkrp1 genes are clustered in a region flanked by A2m and Cd69 genes and that most Ly49 genes are clustered in a distal region -1 Mb distant. Importantly, syntenic intervals of mouse chromosome 6 and human chromosome 12p that include the NKC are conserved. NKC species conservation suggests that the human NKC may contain orthologues for the mouse viral disease resistance genes, Cmv1 and Rmp1. The high-resolution NKC map will facilitate investigation of NKC gene regulation and identification of phenotypically defined gene products that confer NK cell defense against viral pathogens.

Mapping of the IDDM locus Idd3 to a 0.35-cM interval containing the interleukin-2 gene

Currently, 16 loci that contribute to the development of IDDM in the NOD mouse have been mapped by linkage analysis. To fine map these loci, we used congenic mapping. Using this approach, we localized the Idd3 locus to a 0.35-cM interval on chromosome 3 containing the Il2 gene. Segregation analysis of the known variations within this interval indicated that only one variant, a serine-to-proline substitution at position 6 of the mature interleukin-2 (IL-2) protein, consistently segregates with IDDM in crosses between NOD and a series of nondiabetic mouse strains. These data, taken together with the immunomodulatory role of IL-2, provide circumstantial evidence in support of the hypothesis that Idd3 is an allelic variation of the Il2 gene, or a variant in strong linkage disequilibrium.

Effect of natural sequence variation at the H-2Ld-restricted CD8+ T cell epitope of the murine cytomegalovirus ie1-encoded pp89 on T cell recognition

The amino acid sequence YPHFMPTNL of pp89, the ie1-encoded product of murine cytomegalovirus (MCMV; Smith strain), constitutes an immunodominant T cell epitope recognized in association with H-2Ld. Nucleotide sequencing of MCMV isolates derived from wild mice identified variation between amino acids 147-192 of pp89 in 19 of 27 isolates, including the region encompassing the CTL epitope (amino acid residues 168-176). Four groups of isolates with naturally occurring variant sequences for the CTL epitope were defined: (1) YPHFMPPNL; (2) YPHFMPPSL; (3) YPHFIPPSL; and (4) YLDFMPPNL. The remaining isolates, and the laboratory strains K181 and Vancouver, showed complete identity with the Smith strain. Polyclonal pp89 (Smith strain)-specific CTL only weakly recognized target cells infected with MCMV from most variant groups. No lysis of cells infected with isolate N1 from group 4 was detected. Analyses of cross-reactive recognition of YPHFMPTNL peptide-coated targets by CTL primed with variant MCMV isolates showed that the group 2 and 3 isolates, G4 and K6, respectively, but not the group 4 isolate N1, elicited CTL that exhibited a cross-reactive response. Furthermore, while the group 2 and 3 isolates G4 and K6 were able to prime CTL responses that displayed reactivity to homologous pp89 variant nonapeptides, the group 4 isolate N1 failed to do so. Finally, while immunization of mice with the nonapeptide YPHFMPTNL conferred significant protection against the laboratory strain K181 [correction of Kl81], no evidence of protection was observed for the group 2 and 4 variants G4 and N1, respectively. These observations raise the possibility that clinical isolates of HCMV may also differ in sequence from potential vaccine strains at immunodominant epitopes for CD8+ T cells thus reducing the efficacy of vaccination.

Assessment of antigenicity and genetic variation of glycoprotein B of murine cytomegalovirus

An analysis of linear antibody-binding sites of the glycoprotein B (gB) molecule of murine cytomegalovirus (MCMV) and of genetic variation within these regions was performed. To achieve this, a series of overlapping fragments spanning the entire coding sequence of the gB gene of the K181 strain of MCMV was expressed in E. coli as fusion proteins with glutathione S-transferase (GST) using the pGEX expression system. Four antibody-binding regions were mapped to locations spanning amino acid residues 17-79 (BS), 155-278 (BE2), 809-926 (SS) and 347-508 (BB and EE), based on reactivity in Western blot analysis of GST-gB fusion proteins with murine polyclonal antiserum raised against MCMV. Only the antibody-binding region BE2 (155-278) elicited an antiserum that exhibited complement-dependent neutralizing activity, and immunization of mice with the fusion protein BE2 led to moderate but significant reductions in the level of MCMV replication in the spleen. Polyclonal antisera raised against the GST-gB fusion proteins detected purified virion proteins of 105 kDa (anti-BS and anti-BE2) and 52 kDa (anti-SS) and are therefore likely to recognize the N-terminal and C-terminal portions of the gB molecule, respectively. The antibody-binding region within amino acid residues 17-79 was found to be MCMV strain-specific, whereas antibody-binding regions within residues 155-278 and 809-926 were found to be conserved among MCMV field isolates. Comparative sequence analysis of the corresponding regions of MCMV gB revealed a level and extent of sequence of sequence heterogeneity consistent with these findings.

DNA sequence and transcriptional analysis of the glycoprotein M gene of murine cytomegalovirus

We have characterized the gene encoding the murine cytomegalovirus (MCMV) homologue of the human cytomegalovirus (HCMV) UL100 open reading frame (ORF) that encodes the HCMV glycoprotein M (gM) molecule. It was identified based on its collinearity with MCMV homologues of the HCMV UL99, UL102, UL103 and UL104 ORFs which lie in the HindIII G fragment of the K181 strain of MCMV. Sequencing of a 2.3 kb EcoRI-BamHI subfragment of the EcoRI G fragment adjacent to the EcoRI A fragment revealed the presence of the complete MCMV gM ORF and two incomplete ORFs, which corresponded to homologues of HCMV UL99 and UL102. The MCMV gM ORF consists of 1059 nucleotides and is expressed as a 1.2 kb transcript at late times post-infection. To precisely characterize the gM transcript, the 5' and 3' ends were mapped. It was found that the transcript initiates at nucleotides 740 or 745, and that the site of polyadenylation at nucleotide 1961 occurs downstream of the second potential polyadenylation signal located at nucleotide 1934. Based on these findings the MCMV gM is predicted to consist of 353 residues and when compared with HCMV gM has a 47% level of identity. Of great interest is the finding that the MCMV gM amino acid sequence is completely conserved among six isolates of MCMV that had been shown to exhibit considerable variation both in the MCMV glycoprotein B and the immediate-early 1 gene-encoded pp89 molecule. Thus, this glycoprotein appears to be antigenically conserved.

Genetic mapping of Cmv1 in the region of mouse chromosome 6 encoding the NK gene complex-associated loci Ly49 and musNKR-P1

The Cmv1 resistance gene controls splenic replication of murine cytomegalovirus (MCMV) and confers natural killer (NK) cell-mediated resistance to otherwise lethal infection. The Cmv1 phenotypes of 13 inbred mouse strains have been assessed, and it was found that the Cmv1r resistance phenotype was restricted to the C57BL/6J and Ma/MyJ strains. We have further analyzed the linkage of Cmv1 to the NK gene complex (NKC) mapping to distal mouse chromosome 6 in 99 (BALB/c x C57BL/6J)F1 x BALB/c backcross mice using cloned gene probes and microsatellite markers from this region. No recombinants were observed between Cmv1 and the NKC-associated Ly49 and musNKR-P1 multigene families, nor the Kap locus, nor with 7 microsatellite markers, indicating that Cmv1 is closely linked (< 1 cM) to all of these markers. Analysis of the genotype of the MCMV-susceptible BXD8 RI strain around the NKC region revealed that it had C57BL/6J alleles at microsatellite markers immediately proximal and distal to Cmv1. This suggests that the Cmv1s phenotype of this strain is due to a germ-line mutation. Thus, the close linkage of Cmv1 to the Ly49 and musNKR-P1 multigene families suggests that it may represent an NK cell recognition structure encoded in the NKC region.

Mapping and transcriptional analysis of the murine cytomegalovirus homologue of the human cytomegalovirus UL103 open reading frame

Murine cytomegalovirus (MCMV) has been widely used as a model for human cytomegalovirus (HCMV) infection since the two viruses share many biological and pathogenic properties. To further evaluate the similarities in the genomes of these viruses we have sought to identify MCMV genes that encode immunoreactive proteins by screening a lambda gt11 cDNA library with anti-MCMV monoclonal antibodies (MAb). Clone 430, identified on the basis of its reactivity with the MAb 6/20/1, was completely sequenced and shown to encode the MCMV homologue of the HCMV UL103 open reading frame (ORF). This ORF is encoded by a 1.1-kb transcript that is expressed at late times following infection. Sequencing of the cDNA also revealed the presence of two incomplete ORFs encoding the homologues of the HCMV UL102 and 104 ORFs. These ORFs are encoded by a 2.4-kb leaky late transcript and a 3.0-kb late transcript, respectively. Together these ORFs constitute part of a block of genes conserved in all herpesviruses, and in the MCMV and HCMV genomes this block of genes shows striking positional homology. The high degree of homology between HCMV and MCMV ORFs, at both the nucleotide and amino acid levels, plus the growing evidence of conservation in gene order between the two genomes suggests that the two viruses are very similar at the molecular level.

Identification, sequencing and expression of the glycoprotein L gene of murine cytomegalovirus

DNA sequence analysis of the genome of the Smith strain of murine cytomegalovirus (MCMV) revealed an open reading frame (ORF) with amino acid sequence identity to glycoprotein L (gL) of other herpesviruses. The ORF is 822 bp in size and has the capacity to encode a protein of 274 amino acids. It has significant identity with the gL genes of human CMV and human herpesvirus 6. The coding sequence of the gL gene of MCMV strain K181 was also determined, and expressed in Escherichia coli as a fusion protein with glutathione S-transferase using the pGEX expression system. Two antibody-binding regions were identified on the basis of the reactivity of a series of truncated gL constructs with anti-MCMV antibodies. One was mapped to residues 1 to 38 and the other between residues 230 and 274. Polyclonal antibodies specific to gL were raised against the full-length gL fusion protein. The antisera were shown to react with a 46K protein present in purified virions by Western blotting. Treatment of purified virions with endoglycosidase-H or -F resulted in reductions in M(r) of the 46K species to 42K and 31K, respectively. The antisera did not exhibit any neutralizing activity in a plaque reduction assay.

Expression of the glycoprotein H of murine cytomegalovirus and identification of an N-terminal antibody-binding region

A series of overlapping fragments spanning the entire coding sequence of the gH gene of murine cytomegalovirus (MCMV) were expressed in Escherichia coli as fusion proteins with glutathione S-transferase (GST) using the pGEX expression system. A region of antibody-binding was mapped to the NH2-terminus of glycoprotein H (gH) between amino acid residues 26 and 90 on the basis of the reactivity of GST-gH fusion proteins with polyclonal antibodies to MCMV in Western blot analysis. Antibodies to gH were generated in mice immunized with the GST-gH fusion protein SK and shown to react with an 87-kDa polypeptide present in virion particles which was conserved in MCMV isolates obtained from diverse locations. They also recognized the gH protein in MCMV-infected cells, as well as gH expressed in Chinese Hamster Ovary cells. The antibodies to gH had a significant ELISA titer but no neutralizing activity in vitro. The antibody response to the GST-gH fusion protein did not modify the level of MCMV replication in the spleens of mice.

Identification and characterization of a murine cytomegalovirus gene with homology to the UL25 open reading frame of human cytomegalovirus

Monoclonal antibody 1B4, previously shown to be protective in vivo and to cross-react with both virally encoded and normal host cell proteins, was used to screen a lambda gt11 cDNA derived from mRNA harvested from mouse embryo fibroblasts 24 hr after infection with murine cytomegalovirus (MCMV). A 700-bp cDNA was identified representing the 5'terminus of a 2460-bp open reading frame (ORF) with significant homology to the human cytomegalovirus UL25 ORF. The UL25 ORF of MCMV potentially encodes an 820 amino acid viral tegument protein with an estimated molecular weight of approximately 90 kDa. Amino acid homology with eukaryotic nucleolins was identified in the acidic N-terminal third of the MCMV UL25 proteins, suggesting that the protein may be involved in transcriptional activation or interactions with chromatin. Northern analysis and S1 nuclease data indicated that the gene is expressed late in infection as an approximately 3-kb transcript and that expression is dependent on viral DNA replication. An epitope recognized by MAb 1B4 was identified using recombinant pGEX plasmids expressing fusion proteins representing the N-terminal region of the MCMV UL25 protein. The identification of the MCMV UL25 ORF as a member of the CMV-specific UL25/UL35 gene family provides an opportunity for the investigation of the role these genes and their products in CMV pathogenesis in an animal model.

Effects of galactose feeding on aldose reductase gene expression

Aldose reductase (AR) is implicated in the pathogenesis of the diabetic complications and osmotic cataract. AR has been identified as an osmoregulatory protein, at least in the renal medulla. An outstanding question relates to the response of AR gene expression to diet-induced galactosemia in extrarenal tissues. This paper shows that AR gene expression in different tissues is regulated by a complex multifactorial mechanism. Galactose feeding in the rat is associated with a complex and, on occasions, multiphasic pattern of changes in AR mRNA levels in kidney, testis, skeletal muscle, and brain. These changes are not in synchrony with the temporal sequence of changes in tissue galactitol, galactose, and myoinositol concentrations. Moreover, galactose feeding results in changes in tissue AR activities that are not related, temporally or quantitatively, to the alterations in tissue AR mRNA or galactitol levels. It is concluded that AR gene expression and tissue AR activities are regulated by mechanisms that are not purely dependent on nonspecific alterations in intracellular metabolite concentrations. This conclusion is supported by the finding that chronic xylose feeding, despite being associated with intracellular xylitol accumulation, does not result in alterations in AR mRNA levels, at least in the kidney.

Molecular and biological characterization of new strains of murine cytomegalovirus isolated from wild mice

Studies of the prevalence of antibody to murine cytomegalovirus (MCMV) in free-living wild mice (Mus domesticus) trapped in diverse regions of Australia and on a sub-Antarctic island indicated that 90% of 468 mice had serum antibody to MCMV. Twenty-six field isolates of MCMV were plaque-purified from salivary gland extracts of representative seropositive mice. These isolates varied considerably in their ability to replicate in the salivary glands of weanling BALB/c mice with 9 of 15 failing to reach significant titres in this organ and the titres of the remaining 6 strains varying by at least 100-fold. The high frequency of restriction fragment length polymorphisms observed suggests widespread genetic heterogeneity exists among the strains. This observation was mirrored at the polypeptide level by Western blot analyses with polyclonal antisera to MCMV. The isolation in this study of four genetically distinct strains of MCMV from a single wild mouse and several strains from other individual mice demonstrates that multiple infections with MCMV may be commonplace in wild mice.

Identification of the glycoprotein H gene of murine cytomegalovirus

Partial sequencing of the HindIII C fragment of murine cytomegalovirus (MCMV) revealed an open reading frame of 2172 nucleotides in length encoding a 724 amino acid protein with a predicted Mr of 80.4K. Analysis of the predicted amino acid sequence revealed homology with glycoprotein H (gH) from a number of other herpesviruses. MCMV gH showed strongest amino acid identity with human (H) CMV and human herpesvirus 6 gH, and less identity with the gH protein sequences of Epstein-Barr virus, varicella-zoster virus and herpes simplex virus type 1. The greatest identity between MCMV and HCMV gH occurs in the C-terminal region. The MCMV gH is characterized by having a 14 amino acid signal sequence, a 23 amino acid transmembrane region, a seven amino acid positively charged cytoplasmic anchor sequence and eight putative N-linked glycosylation sites. Comparison of MCMV gH with that of HCMV indicates that there are 12 conserved cysteine residues and three conserved potential N-linked glycosylation sites.

Activation of erythrocyte aldose reductase in man in response to glycaemic challenge

Flux via the polyol pathway, which comprises the enzymes aldose reductase (AR) and sorbitol dehydrogenase (SDH), has been implicated in the debilitating complications of diabetes. Previous studies in this laboratory have indicated that erythrocyte AR activities are increased (by 72%) in insulin-dependent diabetic patients. To investigate the mechanism underlying this activation, the response of AR activity to oral glucose challenge was investigated in eight overnight-fasted human volunteers. Glucose consumption led to a transient activation (by 76%: P less than 0.01) of erythrocyte AR, which paralleled the rise and subsequent fall in blood glucose concentrations. It is concluded that erythrocyte AR activity is acutely modulated in response to hyperglycaemia by an as yet unknown mechanism.

Multicomponent diffusion in dilute solutions of mixed electrolytes

The Onsager-Fuoss theory of ion transport can be used to study multicomponent diffusion in dilute solutions of mixed electrolytes. Precise Lij phenomenological coefficients can be calculated from a knowledge of the solvent properties and limiting ionic conductivities. If activity coefficients for dilute mixed electrolyte systems are available, precise multicomponent diffusion coefficients can also be calculated. Explicit equations are given for calculating both sets of transport coefficients. The equations apply to systems containing an arbitrary number of strong electrolytes and are valid at low total salt concentrations. To illustrate the use of the equations, ternary diffusion in a few aqueous systems is examined in detail. Aqueous mixed electrolyte systems containing H+ exhibit strongly coupled diffusion and highly variable diffusion coefficients. A modified Harned conductimetric experiment is described for the determination of ternary diffusion coefficients in dilute solutions. Results for the system HCl- KCl-H2O are in good agreement with theoretical predictions.