Biomedical subjects

C B Kunst

Publications and source records attributed to C B Kunst.

10 recordsLinked to original sources

PubMed2000

Genetic mapping of a mouse modifier gene that can prevent ALS onset.

Mutations in the cytoplasmic Cu/Zn superoxide dismutase (SOD1) gene on human chromosome 21q22.1 cause 10-20% of familial amyotrophic lateral sclerosis (ALS) cases. The expression of the ALS phenotype in mice carrying the murine G86R SOD1 mutation is highly dependent upon the mouse genetic background. This is similar to the phenotypic variation observed in ALS patients containing identical SOD1 mutations. In the FVB/N background, mice expressing mG86R SOD1 develop an ALS phenotype at approximately 100 days. However, when these mice were bred into a mixed background of C57Bl6/129Sv, the onset of the ALS phenotype was delayed (143 days to >2 years). Using 129 polymorphic autosomal markers in a whole genome scan, we have identified a major genetic modifier locus with a maximum lod score of 5.07 on mouse chromosome 13 between D13mit36 and D13mit76. This 5- to 8-cM interval contains the spinal muscular atrophy (SMA)-associated gene Smn (survival motor neuron) and seven copies of Naip (neuronal apoptosis inhibitory protein), suggesting a potential link between SMA and ALS.

Amyotrophic Lateral Sclerosis↗

PubMed1998

Re-examination of factors associated with expansion of CGG repeats using a single nucleotide polymorphism in FMR1.

In at least 98% of fragile X syndrome cases, the disease results from expansion of the CGG repeat in the 5' end of FMR1. The use of microsatellite markers in the FMR1 region has revealed a disparity of risk between haplotypes for CGG repeat expansion. Although instability appears to depend on both the haplotype and the AGG interspersion pattern of the repeat, these factors alone do not completely describe the molecular basis for the linkage disequilibrium between normal and fragile X chromosomes, in part due to instability of the marker loci themselves. In an effort to better understand the mechanism of dynamic mutagenesis, we have searched for and discovered a single nucleotide polymorphism in intron 1 of FMR1 and characterized this marker, called ATL1, in 564 normal and 152 fragile X chromosomes. The G allele of this marker is found in 40% of normal chromosomes, in contrast to 83% of fragile X chromosomes. Not only is the G allele exclusively linked to haplotypes over-represented in fragile X syndrome, but G allele chromosomes also appear to transition to instability at a higher rate on haplotypes negatively associated with risk of expansion. The two alleles of ATL1 also reveal a highly significant linkage disequilibrium between unstable chromosomes and the 5' end of the CGG repeat itself, specifically the position of the first AGG interruption. The data expand the number of haplotypes associated with FMR1 and specifically allow discrimination, by ATL1 alleles, of single haplotypes with differing predispositions to expansion. Such haplotypes should prove useful in further defining the mechanism of dynamic mutagenesis.

Adenine Nucleotides↗

PubMed1997

Mutations in SOD1 associated with amyotrophic lateral sclerosis cause novel protein interactions.

A subset of familial and sporadic amyotrophic lateral sclerosis (ALS-a fatal disorder characterised by progressive motor neuron degeneration) cases are due to mutations in the gene encoding Cu,Zn superoxide dismutase (SOD1). Two mutations which have been successfully used to generate transgenic mice that develop an ALS-like syndrome are glycine 85 to arginine (G85R) and glycine 93 to alanine (G93A) with the mutant SOD1 allele overexpressed in a normal mouse genetic background. No ALS-like phenotype is observed in mice overexpressing wild-type SOD1 or mice without any SOD1 activity. These dominant mutations, which do not necessarily decrease SOD1 activity, may confer a gain of function that is selectively lethal to motor neurons. The yeast interaction trap system allowed us to determine whether these mutations in SOD1 caused novel protein interactions not observed with wild-type SOD1 and which might participate in the generation of the ALS phenotype. Two proteins, lysyl-tRNA synthetase and translocon-associated protein delta, interact with mutant forms of SOD1 but not with wild-type SOD1. The specificity of the interactions was confirmed by the coimmunoprecipitation of mutant SOD1 and the expressed proteins. These proteins are expressed in ventral cord, lending support to the relevance of this interaction to motor neuron disease.

12E7 Antigen↗

PubMed1997

The effect of FMR1 CGG repeat interruptions on mutation frequency as measured by sperm typing.

Fragile X syndrome results from the unstable expansion of a CGG repeat within the FMR1 gene. Three classes of FMR1 alleles have been identified, normal alleles with 6-60 repeats, premutations with 60-200 repeats, and full mutations with > 230 repeats. Premutations are exquisitely unstable upon transmission. Normal alleles, while generally stable upon transmission, are thought to have different intrinsic mutation frequencies, such that some normal alleles may be predisposed towards expansion while others may be more resistant to such change. One variable that may account for this difference is the occurrence of one or more AGG triplets punctuating the normal CGG repeat. The AGG interruptions lead to alleles that have equivalent overall length but different lengths of perfect repeats. To test the influence of the length of perfect repeats on stability, we examined the CGG repeat of single sorted sperm from two males, each with 39 total repeats, but distinct AGG interruption patterns. Sorted sperm of each donor showed -15% variation in repeat length, consistent with previous studies of sorted sperm at other triplet repeat loci. However, when discounting the majority variation of +/-1 repeat, the male with 29 perfect repeats showed 3% expansion changes while the donor with only 19 perfect repeats had none (< 0.9%). Moreover, > 90% of all variant sperm, including all those observed with expansions, showed expansion or contraction of the 3' end of the repeat array. These data are consistent with the hypothesis that perfect repeat tracts influence the repeat stability and that changes of the FMR1 repeat exhibit polarity.

Fragile X Messenger Ribonucleoprotein 1↗

PubMed1996

FMR1 in global populations.

Fragile X syndrome, a frequent form of inherited mental retardation, results from the unstable expansion of a cryptic CGG repeat within the 5' UTR region of the FMR1 gene. The CGG repeat is normally polymorphic in length, and the content is frequently interrupted by AGG triplets. These interruptions are believed to stabilize the repeat, and their absence, leading to long tracts of perfect CGG repeats, may give rise to predisposed alleles. In order to examine the stability of normal FMR1 alleles, the repeat length of 345 chromosomes from nine global populations was examined with the content also determined from 114 chromosomes as assessed by automated DNA sequencing. The FMR1 alleles, defined by the CGG repeat, as well as by the haplotypes of nearby polymorphic loci, were very heterogeneous, although the level of variation correlated with the age and/or genetic history of a particular population. Native American alleles, interrupted by three AGG repeats, exhibited marked stability over 7,000 years. However, in older African populations, parsimony analysis predicts the occasional loss of an AGG, leading to more perfect CGG repeats. These data therefore support the suggestion that AGG interruptions enhance the stability of the FMR1 repeat and indicate that the rare loss of these interruptions leads to alleles with longer perfect CGG-repeat tracts.

Alleles↗

PubMed1995

Evolution of the cryptic FMR1 CGG repeat.

We have sequenced the 5' untranslated region of the orthologous FMR1 gene from 44 species of mammals. The CGG repeat is present in each species, suggesting conservation of the repeat over 150 million years of mammalian radiation. Most mammals possess small contiguous repeats (mean number of repeats = 8.0 +/- 0.8), but in primates, the repeats are larger (mean = 20.0 +/- 2.3) and more highly interrupted. Parsimony analysis predicts that enlargement of the FMR1 CGG repeat beyond 20 triplets has occurred in three different primate lineages. In man and gorilla, AGG interruptions occur with higher-order periodicity, suggesting that historical enlargement has involved incremental and vectorial addition of larger arrays demarcated by an interruption. Our data suggest that replication slippage and unequal crossing over have been operative during the evolution of this repeat.

Animals↗

PubMed1994

Cryptic and polar variation of the fragile X repeat could result in predisposing normal alleles.

Fragile X syndrome results from the expansion of a CGG repeat that is normally interrupted by occasional AGG triplets. Linkage disequilibrium suggests that certain normal haplotypes may contribute unequally to the pool of fragile X chromosomes. Sequence analysis of normal alleles demonstrates haplotype-specific variation of the cryptic nature of the repeat. Variation occurs principally at the 3' end of the repeat, suggesting stability differences between the leading and lagging strands of DNA replication. Normal alleles with greater than 24 perfect 3' CGG repeats appear more frequently on haplotypes overrepresented among fragile X chromosomes. Such alleles are found in 2% of normal chromosomes and could comprise the ancestral allelic pool from which fragile X chromosomes are derived. These data also may imply that equilibrium between certain predisposed alleles and fragile X expansions has not yet been attained, indicating ongoing evolutionary change at this locus.

Alleles↗

PubMed1994

Loss of mutation at the FMR1 locus through multiple exchanges between maternal X chromosomes.

The mutation observed in the fragile X syndrome, an X-linked inherited disorder causing mental retardation, is almost exclusively an expanded CGG repeat in the first exon of the FMR1 gene. Here we describe a daughter of a female carrier, who inherited the fragile X premutation chromosome based on haplotype analysis using flanking markers. However, the CGG repeat sequence and the intragenic polymorphic marker FMRb showed the normal maternal alleles, while two other intragenic markers, FMRa and FRAXAC2 and other, more distant markers, showed the risk haplotype. Since FMRa and FRAXAC2 are located in between the markers CGG and FMRb, this results in patches of normal and fragile X sequences in the FMR1 gene of the daughter. This observation is very likely due to gene conversion. As this daughter received a normal CGG repeat region, we expect that her risk to have affected offspring is the same as the population risk. The observed phenomenon would therefore represent a back mutation at the FMR1 locus.

Base Sequence↗

PubMed1993

Actin-binding protein (ABP-280) filamin gene (FLN) maps telomeric to the color vision locus (R/GCP) and centromeric to G6PD in Xq28.

Actin-binding protein-280 (ABP-280) is a dimeric actin filament crosslinking protein that promotes orthogonal branching of actin filaments and links actin filaments to membrane glycoproteins. We have mapped the ABP-280 filamin gene (FLN) to Xq28 by Southern blot analysis of somatic cell hybrid lines, by fluorescence in situ hybridization, and through identification of portions of the FLN gene within cosmids and YACs mapped to Xq28. The FLN gene is found within a 200-kb region centromeric to the G6PD locus and telomeric to DSX52 and the color vision locus.

Blotting, Southern↗

PubMed1993

Human and murine FMR-1: alternative splicing and translational initiation downstream of the CGG-repeat.

Fragile X syndrome is associated with massive expansion of a CGG trinucleotide repeat within the FMR-1 gene and transcriptional silencing of the gene due to abnormal methylation. Partial cDNA sequence of the human FMR-1 has been reported. We report here the isolation and characterization of cDNA clones encoding the murine homologue, fmr-1, which exhibit marked sequence identity with the human gene, including the conservation of the CGG repeat. A conserved ATG downstream of the CGG repeat in human and mouse and an in-frame stop codon in other human 5' cDNA sequences demarcate the FMR-1 coding region and confine the CGG repeat to the 5' untranslated region. We also present evidence for alternative splicing of the FMR-1 gene in mouse and human brain and show that one of these splicing events alters the FMR-1 reading frame, predicting isoforms with novel carboxy termini.

Alternative Splicing↗