Of mice and Marfan: genetic linkage analyses of the fibrillin genes,Fbn1 and Fbn2, in the mouse genome

The fibrillin genes, FBN1 and FBN2, encode large extracellular matrix glycoproteins involved in the structure and function of microfibrils. Mutations in FBN1 are found in patients with Marfan syndrome, a heritable connective tissue disease that primarily affects the cardiovascular, ocular, and skeletal systems. We extended the studies of these genes by determining their chromosomal position in the mouse genome. Restriction fragment length polymorphisms (RFLPs) between the progenitors of an interspecific backcross involving AEJ/Gn and Mus spretus mice were used to establish the segregation patterns of the murine homologs, Fbn1 and Fbn2, in the backcross progeny. The results position Fbn1 between the B2m and Illa genes on mouse Chromosome (Chr) 2 and establish its candidacy for the Tight skin (Tsk) mutation. The results position Fbn2 between the D18Mit35 and Pdgfrb loci in the central region of mouse Chr 18. Fbn2 maps near three mutations [bouncy (bc), plucked (pk), and shaker with syndactyly (sy)] and may be a candidate for the pk mutation.     

Neuromuscular degeneration (nmd): a mutation on mouse Chromosome 19 that causes motor neuron degeneration

Neuromuscular degeneration, nmd, is a spontaneous autosomal recessive mutation in the mouse producing progressive hindlimb impairment caused by spinal muscular atrophy. We used an intersubspecific intercross between B6.BKs-nmd ^2J/+ and Mus musculus castaneus (CAST/Ei) to map the nmd mutation to mouse Chromosome (Chr) 19 with the most likely gene order: nmd-(D19Se12, Pygm)-Cntf-Pomc2-D19Mit16-Cyp2c-Got1. nmd maps near muscle deficient, mdf, and has a very similar clinical phenotype, but allele tests and histological differences suggest that nmd is a distinct mutation at a different locus. Although closely linked, nmd recombined with the candidate genes muscle glycogen phosphorylase, Pygm, and ciliary neurotrophic factor, Cntf.     

The ter primordial germ cell deficiency mutation maps near Grl-1 on mouse Chromosome 18

A single recessive gene, ter (teratoma), causes germ cell deficiency and a high incidence of congenital testicular teratomas in the 129/Sv-ter strain of the mouse. Linkage analyses between the ter gene and 36 marker genes of 19 chromosomes were performed with matings between the C57BL/6J-ter congenic strain and four inbred strains. Results showed that the ter gene was linked to D18Mit9, D18Mit14, and D18Mit17 on Chromosome (Chr) 18. Gene order estimated on the basis of recombination distance (in centimorgans) was [centromere-D18Mit14-5.1 (cM)-ter-0 (cM)-D18Mit17-23.8 (cM)-D18Mit9]. D18Mit17 is the microsatellite DNA of the Grl-1 (glucocorticoid receptor-1) locus. We conclude that the ter gene is closely linked to Grl-1 on Chr 18 and is a new mutation involving the developmental modification of primordial germ cells in mice.Deceased     

A new mouse mutation causing male sterility and histoincompatibility

Male sterility and histoincompatibility, mshi, is an autosomal recessive mutation in BALB/cBy mice that causes reduced testis size and sterility in homozygous males. The testes of homozygous mutants are highly disorganized and appear to have a block in the regulation of male germ cell proliferation. No heterozygous effect is detectable. Reproduction is unaffected in females carrying the mutation. The mutation also affects histocompatibility; most homozygous males and females reject sex-matched skin grafts from BALB/cBy mice. We used an intercross between BALB/cBy and CAST/Ei to map the mshi mutation to the proximal end of Chromosome (Chr) 10. The most likely gene order places the mutation between D10Mit80 and D10Mit16, near the interferon gamma receptor locus, Ifgr, which may be a candidate gene for this mutation. Received: 26 April 1996 / Accepted: 20 June 1996     

Mutator activity in uvs mutants of Aspergillus nidulans

Summary The frequency of selenate-resistant spontaneous mutants was determined among the conidia of two uvs ⁺, two allelic uvsB, one uvsD, three allelic uvsC and three allelic uvsE strains of Aspergillus nidulans. In the uvsB, uvsD, uvsC and uvsE mutants the median frequencies of mutation were respectively 1.7, 1.8, 8.7 and 4.0 times as high as in the uvs ⁺ strains. The selenate resistance resulted from mutation at the chromosomal loci sB or sC. It is concluded that the uvs alleles enhance spontaneous mutation in chromosomal genes.     

Neuromuscular ataxia: a new spontaneous mutation in the mouse

Neuromuscular ataxia, nma, is a new autosomal recessive mutation that arose spontaneously in CBA/J inbred mice at The Jackson Laboratory. The mutation, now maintained on the B6C3FeF₁ hybrid background, when homozygous, causes small size, uncoordinated gait, dysmetria, dystonia, general weakness, and death shortly after weaning. No biochemical or morphological abnormalities have been detected. We used an intercross between the B6C3FeF₁ mutant and CAST/Ei to map the nma mutation to the proximal end of Chr 12. The most likely gene order places the mutation between D12Mit270 and D12Mit54, non-recombinant with D12Mit2 in 96 tested meioses. Received: 27 March 2000 / Accepted: 17 May 2000     

The role of melanocyte-stimulating hormone (MSH) receptor in bovine coat color determination

The melanocyte-stimulating hormone (MSH) receptor has a major function in the regulation of black (eumelanin) versus red (phaeomelanin) pigment synthesis within melanocytes. We report three alleles of the MSH-receptor gene found in cattle. A point mutation in the dominant allele E ^D gives black coat color, whereas a frameshift mutation, producing a prematurely terminated receptor, in homozygous e/e animals, produces red coat color. The wild-type allele E ⁺ produces a variety of colors, reflecting the possibilities for regulating the normal receptor. Microsatellite analysis, RFLP studies, and coat color information were used to localize the MSH-receptor to bovine Chromosome (Chr) 18.     

Tli1, a resistance locus for carcinogen-induced T-lymphoma

Within 180 days after injection with N-methyl-N-nitrosourea (MNU), 83.5% of AKR/J mice and 37.5% of BALB/cJ mice developed T-lymphoma. The high tumor incidence was a dominant trait, as 93% of MNU-injected F₁ mice developed T-lymphoma. A genome screen of 285 MNU-injected F₂ mice identified a locus, designated T-lymphoma Induced 1 or Tli1, in a ∼10-cM interval on central Chr 1 between D1Mit87 and D1Mit423 with significant linkage to the incidence of MNU-induced T-lymphoma (P= 0.0004). Injection of BALB/cJ.AKR/J–Tli1 congenic mice with MNU confirmed the presence of Tli1 on central Chr 1. Mice homozygous for the BALB/cJ allele (Tli1 ^bb) were over-represented in the tumor-free F₂ mice, while the inheritance of parental alleles of Tli1 in tumor-bearing mice was close to expected. This suggests that the Tli1 ^b allele is recessive and suppresses MNU-induced T-lymphoma development in BALB/cJ mice and in Tli1 ^bb F₂ mice. Furthermore, the kinetics of lymphoma development in BALB/cJ and the Tli1 congenic mice suggests that Tli1 ^b acts to suppress lymphomas developing late after injection with MNU. Two known genes that map in the identified genomic interval on central Chr 1 are candidates for Tli1:IL10, encoding the lymphokine IL10, and Cmkar4, encoding the chemokine receptor CXCR4. Received: 2 November 1998 / Accepted 12 January 1999     

mdfw:A Deafness Susceptibility Locus That Interacts with Deaf Waddler (dfw)

The deaf waddler (dfw) mutation is a model system to study the biology of neuroepithelial hearing defects in mice. Here we describe the identification and characterization of a new allele of deaf waddler (dfw^2J) and present evidence for a hearing susceptibility locus (mdfw) that interacts withdfw.We found that CBy-dfw^2J/dfw^2Jhomozygotes exhibit no discernible auditory brainstem responses (ABR) to sound pressure level stimuli up to 100 dB, indicating a profound deafness. Interestingly, the ABR in CBy-dfw^2J/+ heterozygotes is also abnormal, showing age-dependent elevated thresholds characteristic of a progressive hearing loss. When outcrossed onto the CAST/Ei strain, only 24% of the F2 CBy/CAST-dfw^2J/+ heterozygotes displayed increased ABR thresholds, suggesting that a second locus, controlling hearing function indfw^2J/+ heterozygotes, was segregating in the CBy/CAST-dfw^2Jintercross. By linkage analysis, we localized this locus (mdfw) to Chromosome 10, between markersD10Mit127andD10Mit185,within a 4.0 ± 1.1 cM genetic interval. All CBy/CAST-dfw^2J/+ heterozygotes that develop hearing loss are homozygous for the CBy-derived recessive allele (mdfw^C). In contrast, CBy/CAST-dfw^2J/+ heterozygotes expressing even a single copy of the CAST/Ei-derivedmdfwallele (Mdfw) retain their normal hearing function. Our results reveal an epistatic relationship between themdfwand thedfwgenes and provide a model system to study nonsyndromic hearing loss in mice.     

Cerebellar deficient folia (cdf): A new mutation on mouse Chromosome 6

Cerebellar deficient folia, cdf, is a spontaneous autosomal recessive mutation in the mouse with unique pathology; the cerebellar cortex of the cdf/cdf mouse has only 7 folia instead of 10, which is the normal count for the C3H/HeJ strain in which this mutation arose. The cerebellum of the cdf/cdf mouse is hypoplastic and contains mineral deposits in the ventral vermis that are not present in controls. We used an intersubspecific intercross between C3H/HeSnJ-cdf/+ and Mus musculus castaneus (CAST/Ei) to map the cdf mutation to Chromosome (Chr) 6. The most likely gene order is D6Mit16–(cdf, D6Mit3)–D6Mit70–D6Mit29–D6Mit32, which positions cdf distal to lurcher (Lc) and proximal to motor neuron degeneration 2 (mnd2). The definitive visible phenotypes and histopathologies of cdf, Lc, and mnd2 support our mapping evidence that cdf is a distinct gene. The novel pathology of cdf should help elucidate the complicated process of cerebellar folia patterning and development. cdf recombined with mouse atonal homolog 1, Math1, the mouse homolog of the Drosophila atonal gene. Received: 2 August 1996 / Accepted: 2 October 1996     

Genetic and phenotypic analysis of Tcm, a mutation affecting early eye development

Tcm (total cataract with microphthalmia) is an autosomal dominant mouse eye mutation. Heterozygous Tcm/+ mice are born with several eye malformations including microphthalmia, retinal and iris dysplasia, total lens cataract, and ventral coloboma. The Tcm mutation was previously mapped to a 26-Mb region on Chr 4 between D4Mit235 and D4Mit106. In this study, we characterize the Tcm/Tcm homozygous mutant and find they are viable but severely microphthalmic. The developing eye in the Tcm/Tcm homozygote shows defects during early eye development, before formation of the optic cup. Further genetic mapping reduced the Tcm critical region to a 1.3-Mb region bordered by SNPs rs3666764 and rs3713818. This critical region contains two known genes (Asph and Gfd6) and three predicted genes, all of which are positional candidates for Tcm. Sequence analysis of Tcm genomic DNA revealed no mutations in the coding regions and splice site junctions of the five candidate genes. These results indicate that the causitive Tcm mutation falls within a noncoding regulatory region of one of the five candidate genes or in an undescribed gene.     

Mutations of the Mouse Twist and sy (Fibrillin 2) Genes Induced by Chemical Mutagenesis of ES Cells

A prior phenotype-based screen of mice derived from ethylmethanesulfonate-mutagenized embryonic stem cells yielded two mouse limb defect mutants. Animals heterozygous for the polydactyly ems (Pde) mutation display preaxial polydactyly of the hindlimbs, and homozygous syndactyly ems (sne) animals are characterized by a fusion of the middle digits of their hindlimbs and sometimes forelimbs. We now report that Pde is a new allele of the basic helix-loop-helix protein gene Twist. Sequencing the full-length cDNA and several hundred basepairs of genomic DNA upstream of the coding region failed to reveal a mutation, suggesting that the lesion may be in a regulatory element of the gene. sne is a new fused phalanges (fp) allele of the shaker-with-syndactylism deletion complex (sy), and we show that the genomic lesion is a small deletion removing an entire exon, coincident with the insertion of the 3′ end of a LINE element belonging to the T_F subfamily.     

A novel mouse Chromosome 2 congenic strain with obesity phenotypes

Linkage studies have identified many chromosomal regions containing obesity genes in mice. However, only a few of these quantitative trait loci (QTLs) have been used to guide the production of congenic mouse strains that retain obesity phenotypes. We seek to identify chromosomal regions containing obesity genes in the BSB model of spontaneous obesity because the BSB model is a multigenic obesity model. Previous studies identified QTLs on Chromosomes (Chrs) 2, 6, 7,12, and 15. BSB mice are made by backcross of lean C57BL/6J × Mus spretus. F₁s were backcrossed to C57BL/6J mice to produce BSB progeny. We have constructed a new BSB cross and produced congenic mice with obesity phenotypes by marker-directed selection called B6.S–D2Mit194–D2Mit311. We found a highly significant QTL for percentage body lipid on Chr 2 just proximal to the Agouti locus. Chr 2 congenics were constructed to determine whether the main effects would be detectable. We observed highly significant linkage of the Chr 2 congenic containing Agouti and containing markers distal to D2Mit311 and proximal to D2Mit194. Thus, this congenic contains approximately 14.6 cM or 30 Mb (about 1.1% of the spretus mouse genome) and several hundred genes. The obesity phenotype of the QTL is retained in the congenic. The congenic can now be used to model the genetic and physiological basis for a relatively simple, perhaps monogenic, obesity.     

Genetic localization and transmission of the mouse osteopetrotic grey-lethal mutation

The grey-lethal (gl) mouse is the most relevant animal model for recessive osteopetrosis, a genetic defect affecting bone resorption. To localize the gl gene, two novel backcrosses between the gl mutant strain GL/Le dl ^J +/+gl and with the Mus spretus or the Mus m. molossinus have been generated and typed with 19 DNA markers representative of genes or microsatellites. In the Mus m. molossinus backcross, the gl locus cosegregates with the D10Mit108,109,184,193,254,255 markers within a 1 centimorgan genetic interval between the markers (D10Mit54,55,215,Cd24a) and D10Mit148. Our results have also eliminated all the five candidate genes previously localized to this region (Braf-rs1, Fyn, Cd24a, Ros1, and Gja1). On the Mus spretus background, segregation distortion due to a ∼threefold differential survival resulted in a severe deficit in gl/gl animals, indicating the presence of modifier genes. We have also characterized nine cosegregating microsatellite markers closely linked to gl as defined by their specific polymorphisms for the Chromosome (Chr) 10 harboring the gl mutation. Screening of several mouse inbred strains for these polymorphic markers revealed an identical pattern between gl and 129/SvEms, suggesting that the gl mutation arose on this genetic background. The linkage between this polymorphic region and the gl locus provides an entry point to produce a physical map to isolate the gl gene. Received: 23 June 1998 / Accepted: 17 November 1998     

Molecular markers near two mouse Chromosome 13 genes,muted and pearl,which cause platelet storage pool deficiency (SPD)

The recessive muted (mu) and pearl (pe) mutations on Chromosome (Chr) 13 cause pigment dilution and platelet storage pool deficiency (SPD) in mice. In addition, mu causes inner ear abnormalities and pe has symptoms associated with night blindness. Using an interspecific backcross involving the wild-derived Mus musculus musculus (PWK) stock, we have mapped 33 microsatellite markers and four cDNAs relative to mu, pe, and another recessive mutation, satin (sa). Analyzing a total of 528 backcross offspring, we found tight linkage between the pigment loci and several microsatellite markers (D13Mit87, D13Mit88, D13Mit137 with mu; and D13Mit104, D13Mit160, D13Mit161, and D13Mit169 with pe). These markers should aid the eventual molecular identification of these specific SPD genes.     

A high-resolution genetic map around waltzer on mouse Chromosome 10 and identification of a new allele of waltzer

A new autosomal recessive mouse mutation characterized by deafness and circling behavior was recovered during mutagenesis experiments with chlorambucil (CHL). On the basis of allelism tests and linkage analyses, this mutation appears to represent a new allele of waltzer (v) that maps to mouse Chromosome (Chr) 10. We have designated this new allele, Albany waltzer (v ^Alb ). A high-resolution map of the region around v was constructed from data from two intersubspecific backcrosses involving Mus musculus castaneus. The analysis of 648 backcross mice has allowed v ^Alb to be localized 1.1 ± 0.4 cM distal to D10Mit60 and 0.2 ± 0.2 cM proximal to a cluster of four markers, D10Mit172, D10Mit112, D10Mit48, and D10Mit196. An independent backcross was used to confirm the map order and distances in the v ^Alb backcross. The two linkage maps were consistent, indicating that the lesion in v ^Alb , which is presumed to be a deletion based on the known action of CHL, is small and has not significantly altered the map at this level of detection. Additionally, three genes (Ros1, Grik2, and Zfa) were eliminated as possible candidates for v ^Alb , and several SSLP markers were separated genetically. Received: 3 July 1996 / Accepted: 13 August 1996     

Gaping lids, gp, a mutation on centromeric Chromosome 11 that causes defective eyelid development in mice

In mammals, during fetal development, the eyelids grow and flatten over the eyes and temporarily fuse closed. Failure of this normal developmental process in mice leads to the defect, open-eyelids-at-birth. Nearly all newborns of the GP/Bc strain, homozygous for the spontaneous recessive mutation, gaping lids (gp), have bilateral open eyelids at birth, with essentially no fusion between the upper and lower eyelids. Histological sections and scanning electron microscopy of GP/Bc eyes during the normal period of eyelid growth and fusion indicate that gp/gp mutant fetuses have deficient upper and lower eyelids; surface periderm cells that appear to have some role in eyelid growth and fusion are present, but lack a normal ``streaming' pattern toward the fusion zone. No other defects due to the gaping lids mutation were detected. A genetic analysis based on outcrosses of GP/Bc to various linkage marker stocks and to CBA/J and ICR/Bc normal strains was done. Penetrance in F₂ segregants, but not in BC1 segregants, was usually significantly less than 100%, was strongly affected by the identity of the normal strain used, ranging from 44% to 92%, and indicated a potential complexity of modifiers. Forty-one affected F₂ and 120 BC₁ segregants from the outcross of GP/Bc to CBA/J, and 23 affected F₂ segregants from the outcross to ICR/Bc, were used to map gp to proximal Chr 11 between the centromere and D11Dal1 (Camk2b), an interval previously defined as less than 1 cM. Sets of whole F₂ litters from the crosses to CBA/J (n = 106) and ICR/Bc (n = 65) strains were typed for informative SSLPs near gp (D11Mit62 and D11Mit74, respectively) and demonstrated that the segregation ratios in the region are Mendelian. The known genes in the interval, Nf2 and Lif, do not seem to be obvious candidate genes for gp. An Egfr-null allele was used to confirm the previously reported map position of the potential candidate locus, Egfr, to a more distal interval, between D11Mit62/226 and D11Mit151, from which gp had been excluded. Tests for allelism showed that the Egfr mutation and the gp mutation complement each other, and therefore also indicate that they are at different gene loci. Open-eyelids-at-birth is associated with several mutations at other loci with variable penetrance owing to modifiers and in other more complex genetic liabilities in inbred strains, and the genetics of this trait is a model for other genetically complex developmental threshold traits. The gaping lids mutation identifies a previously unknown locus on proximal Chromosome (Chr) 11 that has a strong role in fetal eyelid growth. Received: 13 January 2000 / Accepted: 23 February 2000     

Genetic mapping near the myd locus on mouse Chromosome 8

Myodystrophy (myd), an autosomal recessive mutation of the mouse characterized by progressive weakness and dystrophic muscle histology, maps to the central portion of Chromosome (Chr) 8 (Lane et al. J. Hered 67, 135, 1976). This portion of Chr 8 contains the genes for a mitochondrial uncoupling protein (Ucp) and kallikrein (Kal3), which map to distal 4q in the human, providing evidence for a segment of homology. Characteristics of the myd phenotype coupled with this homology suggest that myd may be a mouse homolog of facioscapulohumeral muscular dystrophy (FSHD), which maps to human 4q35. We have confirmed and expanded the region of mouse 8-human 4 homology by generating a map of Chr 8 in an interspecific backcross of C57BL/6J and a partially inbred strain derived from M. spretus. The map is comprised of the genes for Ucp, coagulation factor XI (Cf11), and chloride channel 5 (Clc5), all of which have homologs on distal human 4q, 15 microsatellite loci, and the membrane cofactor protein pseudogene (Mcp-ps). To place myd in the genetic map, 75 affected progeny from an intersubspecific backcross of animals heterozygous for myd with Mus musculus castaneus were genotyped with Chr 8 microsatellite loci. The mutation maps between D8Mit30 and D8Mit75, an interval that is flanked by genes with human homologs at distal 4q. These results are consistent with the possibility that myd is the mouse homolog of FSHD.     

A rat homolog of the mouse deafness mutant jerker (je)

An autosomal recessive deafness mutant was discovered in our colony of Zucker (ZUC) rats. These mutants behave like shaker-waltzer deafness mutants, and their inner ear pathology classifies them among neuroepithelial degeneration type of deafness mutants. To determine whether this rat deafness mutation (−) defines a unique locus or one that has been previously described, we mapped its chromosomal location. F₂ progeny of (Pbrc:ZUC × BN/Crl) A/a B/b H/h+/− F₁ rats were scored for coat color and behavioral phenotypes. Segregation analysis indicated that the deafness locus might be loosely linked with B on rat Chromosome (Chr) 5 (RNO5). Therefore, 40 −/− rats were scored for BN and ZUC alleles at four additional loci, D5Mit11, D5Mit13, Oprd1, and Gnb1, known to map to RNO5 or its homolog, mouse Chr 4 (MMU4). Linkage analysis established the gene order (cM distance) as D5Mit11–(19.3)–B–(17.9)–D5Mit13–(19.2)–Oprd1–(21.5) − (1.2) Gnb1, placing the deafness locus on distal RNO5. The position of the deafness locus on RNO5 is similar to that ofjerker (je) on MMU4; the phenotypes and patterns of inheritance of the deafness mutation and je are also similar. It seems likely that the mutation affects the rat homolog of je. The rat deafness locus should, therefore, be named jerker and assigned the gene symbol Je. Received: 13 June 1995 / Accepted: 4 January 1996     

The stumbler mutation maps to proximal mouse Chromosome 2

The cerebellar mouse mutation stumbler (stu) was mapped to proximal Chromosome (Chr) 2 with a recently developed polymerase chain reaction assay for endogenous retroviruses that vary between mouse strains. The stu locus resides between the markers D2Mit5 and D2Mit7. A number of developmentally or neurologically relevant candidate genes map in this region, including Bmi1, Dbh, Grin1, Notch1, Pax8, Rxra, and Spna2. Knowing the chromosomal localization of stu should simplify maintenance of the stumbler mouse stock and also enable analysis of the cerebellar defect in presymptomatic individuals.