Jason H. Slingsby

Identification of intervals on chromosomes 1, 3, and 13 linked to the development of lupus in BXSB mice

OBJECTIVE To identify intervals containing systemic lupus erythematosus (SLE) susceptibility alleles in the BXSB strain of mice. METHODS We analyzed 286 (B10 x [B10 x BXSB]F1) backcross mice for a range of phenotypic traits associated with the development of SLE in BXSB mice. The mice were genotyped using 93 microsatellite markers, and the linkage of these markers to disease was studied by extreme-phenotype and quantitative trait locus analysis. RESULTS The disease phenotype in these backcross mice was less severe than that in BXSB mice. However, antinuclear antibody production was increased compared with the parental strain. We identified 4 areas of genetic linkage to disease on chromosome 1 (Bxs1-4), 1 on chromosome 3 (Bxs5), and another interval on chromosome 13 which were associated with various aspects of the phenotype. Bxs4 and Bxs5 are located in regions not previously linked to disease in other models of SLE. CONCLUSION SLE in the BXSB mouse model has a complex genetic basis and involves at least 5 distinct intervals located on chromosomes 1 and 3. There is evidence that different intervals affect particular aspects of the SLE phenotype.

New microsatellite polymorphisms identified between C57BL/6, C57BL/10, and C57BL/KsJ inbred mouse strains

The C57BL/6 (B6) and C57BL/10 (B10) inbred mouse strains are among the most commonly used in biological research and have provided the genetic background for the construction of many congenic strains. The two substrains were derived from the parental C57BL stock and were separated prior to 1937. Since then, they have been thought to possess a very close genetic relationship. By 1992, 161 loci had been tested, and only three differed between B6 and B10: the minor histocompatibility locus H9, the immunoglobulin heavy chain locus Igh 2 on chromosome 12, and the delta-aminolevulinate dehydratase Lv locus on chromosome 4. B6 and B10 have also been shown to differ over an 8 cM segment on chromosome 4. Due to the differences at the H9 locus, B6 and B10 are not histocompatible. The aim of our study was to identify novel genetic polymorphisms between B6 and B10 mice and to analyze the BKs mouse with genetic markers such that further information can be gathered on the genetic origins of this strain. 13 refs., 3 figs.

Polymorphism in the Ly-17 alloantigenic system of the mouse FcgRII gene.

The FcγRII protein is composed of two immunoglobulinlike extracellular domains (EC1 and EC2), a transmembrane (TM) domain, and a cytoplasmic tail encoded by three exons (IC1, IC2 and IC3) (Hogarth et al. 1991). The protein exists as four isoforms, generated by alternative splicing of mRNA transcripts. FcγRIIB1 contains all exons, whereas FcγRIIB2 lacks 47 amino acids encoded by IC1 (Hogarth et al. 1991). FcγRIIB3 is a secreted form of the receptor, and lacks sequences from the TM and IC1 exons (Tartour et al. 1993). FcγRIIB19 is generated by a splicing event involving a cryptic splice donor site in IC1 causing the deletion of the last 84 nucleotides of this exon (Latour et al. 1996). Polymorphism of mouse FcγRII also exists at the level of the gene in the form of the Ly-17 alloantigenic system (Hibbs et al. 1985). The mouse Ly-17 locus has two alleles, Ly-17a and Ly-17b, encoding the Ly-17.1 and Ly-17.2 antigens, respectively. The molecular basis of the Ly-17 alloantigenic system has been investigated (Lah et al. 1990). Two single nucleotide substitutions were observed in the EC2 domain. These were a T to C transition at position 486 and a T to A transversion at position 621. Thus, Pro116 and Gln161 were found in the Ly-17.1 protein, whereas Leu116 and Leu161 were found in the Ly-17.2 protein. Mouse FcγRII is encoded by a single gene on chromosome 1 at 92 cM, and this region has been implicated in autoantibody production and the development of renal disease in lupus-prone mouse strains (Kono et al. 1994; Morel et al. 1994; Drake et al. 1995; J. H. Slingsby and co-workers, unpublished data). We sequenced the complete coding region of FcγRII in 15 mouse strains, in order to confirm the previous findings and to determine whether the two alleles of the FcgRII gene

Murine D17H6S45 (Rd) gene: polymorphism and overlap with complement factor B.

Species: Mouse Locus name: methionine synthase or 5-methyltetrahydrofolatehomocysteine methyltransferase Locus symbol: Mtr Map position: proximal–D13Mit1–1.06 cM ± 1.06 SE–Mtr, D13Bir4, D13Bir6–1.06 ± 1.06–D13Abb1e–2.13 ± 1.49–D13Bir7–distal Method of mapping: Mtr was localized by RFLP analysis of 96 animals from an interspecific backcross panel ((C57BL/6JEi × SPRET/Ei)F1 × SPRET/Ei) provided by The Jackson Laboratory, Bar Harbor, Me. (BSS panel) [1]. Database deposit information: The data are available from the Mouse Genome Database, accession number MGD-JNUM-39061. Molecular reagents: A 1095-bp mouse cDNA was obtained by reverse transcription/PCR of mouse liver RNA, with degenerate oligonucleotides based on regions of homology within the methionine synthase sequences of lower organisms. The two primers (D1730 and D1733), as described by Leclerc et al. [2], were successful in amplifying both human and mouse cDNAs. The PCR products from both species were subcloned and sequenced; they showed 89% identity. The mouse cDNA was labeled by random priming and hybridized to Southern blots of EcoRI-digested mouse genomic DNA. Allele detection: Allele detection was performed by RFLP analysis of an EcoRI polymorphism. The C57BL/6J strain has alleles of approximately 13 kb, while the Mus spretus strain has alleles of approximately 9 kb and 4 kb. A constant band of approximately 0.5 kb was seen in both strains. Previously identified homologs: Human MTR has been mapped to chromosomal band 1q43 by fluorescence in situ hybridization [2–4]. Discussion: Methionine synthase (EC 2.1.1.13, 5-methyltetrahydrofolate-homocysteine methyltransferase) catalyzes homocysteine remethylation to methionine, with 5-methyltetrahydrofolate as the methyl donor and methylcobalamin as a cofactor. Nutritional deficiencies and genetic defects in homocysteine metabolism result in varying degrees of hyperhomocysteinemia. Dramatic elevations in plasma and urinary homocysteine levels are associated with the inborn error of metabolism, homocystinuria. Consequent to the recent isolation of the human cDNA for methionine synthase [2–4], two groups of investigators have identified mutations in methionine synthase in homocystinuric patients [2, 5]. Mild elevations in plasma homocysteine are thought to be a risk factor for both vascular disease and neural tube defects [6–8]. A genetic variant in methylenetetrahydrofolate reductase (MTHFR), the enzyme that synthesizes 5-methyltetrahydrofolate for the methionine synthase reaction, is the most common genetic determinant of hyperhomocysteinemia identified thus far [9]. Mild defects in the methionine synthase reaction are also potential candidates for hyperhomocysteinemia and the associated multifactorial diseases. A common variant has been reported for the human methionine synthase gene, but its physiologic consequences have not yet been determined [2, 4]. The mapping of the human MTR gene to 1q43 and of the mouse gene to proximal Chromosome (Chr) 13 is consistent with previous findings of human/mouse homologies between these 2 chromosomal regions; the human and mouse nidogen genes have been mapped to 1q43 and proximal Chr 13, respectively [10]. Several genes have already been implicated in neural tube defects in mice [11]. Studies involving the mouse methionine synthase gene will be useful in assessing the role of this important enzyme in the development of birth defects and/or vascular disease.