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PubMed1996

Molecular and functional characterization of Slide, an Ac-like autonomous transposable element from tobacco.

A new transposable element of tobacco, Slide, was isolated from the tl mutant line, which shows somatic instability, after its transposition into a locus encoding nitrate reductase (NR). The Slide-124 element is 3733 bp long and its coding sequences show similarities with conserved domains of the transposases of Ac, Tam3 and hobo. Excision from the NR locus is detectable in somatic leaf tissues and Slide mobility is triggered by in vitro tissue culture. Slide excision events create footprints similar to those left by Ac and Tam3. Tobacco lines derived from the tl mutant line seem characterized by unmethylated copies of a few members of the highly repetitive Slide family. Slide mobility was monitored in transient expression assays. In wild-type tobacco protoplasts, the complete Slide element, as well as a defective copy, is able to excise. The complete Slide element, but not the defective version, is able to excise in protoplasts of the heterologous species lettuce (Lactuca sativa). These results show that Slide carries the functions required for its own mobility, and represents the first autonomous Ac-like element characterized in Solanaceae species.

Amino Acid Sequence↗
PubMed2005

Activation of the ALT pathway for telomere maintenance can affect other sequences in the human genome.

Immortal human cells maintain telomere length by the expression of telomerase or through the alternative lengthening of telomeres (ALT). The ALT mechanism involves a recombination-like process that allows the rapid elongation of shortened telomeres. However, it is not known whether activation of the ALT pathway affects other sequences in the genome. To address this we have investigated, in ALT-expressing cell lines and tumours, the stability of tandem repeat sequences known to mutate via homologous recombination in the human germline. We have shown extraordinary somatic instability in the human minisatellite MS32 (D1S8) in ALT-expressing (ALT+) but not in normal or telomerase-expressing cell lines. The MS32 mutation frequency varied across 15 ALT+ cell lines and was on average 55-fold greater than in ALT- cell lines. The MS32 minisatellite was also highly unstable in three of eight ALT+ soft tissue sarcomas, indicating that somatic destabilization occurs in vivo. The MS32 mutation rates estimated for two ALT+ cell lines were similar to that seen in the germline. However, the internal structures of ALT and germline mutant alleles are very different, indicating differences in the underlying mutation mechanisms. Five other hypervariable minisatellites did not show elevated instability in ALT-expressing cell lines, indicating that minisatellite destabilization is not universal. The elevation of MS32 instability upon activation of the ALT pathway and telomere length maintenance suggests there is overlap between the underlying processes that may be tractable through analysis of the D1S8 locus.

Cell Line, Tumor↗
PubMed2001

Beta-catenin activation through mutation is rare in rectal cancer.

Increased transcriptional activation through beta-catenin stabilization plays a central role in colorectal tumorigenesis. Alterations of phosphorylation sites within the CTNNB1 gene, which codes for beta-catenin has been reported to occur in about one-half of colorectal tumors without APC-gene mutations. We assessed the importance of mutations in the regulatory domain, located within exon 3 of CTNNB1, in 103 rectal carcinomas and correlated these data with presence of microsatellite instability, somatic frame-shift alterations of the TCF-4 gene, and APC-gene mutations in the tumors. No mutation was detected in exon 3 of the CTNNB1 gene and our results thus demonstrate that beta-catenin activation through mutation rarely contributes to the development of sporadic and microsatellite instability stable rectal cancer.

Adenocarcinoma↗
PubMed1988

Regulation of Mu element copy number in maize lines with an active or inactive Mutator transposable element system.

In the progeny of an active Mutator plant, the number of Mu elements increases on self-pollination and maintains the average parental Mu content on outcrossing to a non-Mutator line; both patterns of transmission require an increase in the absolute number of Mu elements from one generation to the next. The same average copy number of Mu elements is transmitted through the male and female, but there is wide variation in the absolute copy number among the progeny. In inactive Mutator plants-defined both by the loss of somatic instability at a reporter gene (bronze2-mu1) and by modification of the HinfI sites in the terminal inverted repeat sequences of Mu elements - the absolute copy number of Mu elements is fixed in the parent. Thus, in outcrosses Mu element number is halved, and on self-pollination Mu copy number is constant. Reactivation of somatic mutability at cryptic bz2-mu1 alleles in inactive individuals by crossing to an active line seems not to involve an increase in Mu element copy number transmitted by the inactive individual. These and other results suggest that increases in Mu copy number occur late in plant development or in the gametophyte rather than after fertilization.

DNA Transposable Elements↗
PubMed1991

Cloning of the Mutator transposable element MuA2, a putative regulator of somatic mutability of the a1-Mum2 allele in maize.

The identification of the autonomous or transposase-encoding element of the Mutator (Mu) transposable element system of maize is necessary to the characterization of the system. We reported previously that a transcript homologous to the internal region of the MuA element is associated with activity of the Mutator system. We describe here the cloning of another Mu element, designated MuA2, that cosegregates with Mutator activity as assayed by somatic instability of the a1-Mum2 allele. The MuA2 element has features typical of the transposable elements of the Mutator family, including the 210-bp terminal inverted repeats. Several lines of evidence suggest that MuA2 is an autonomous or transposase-encoding element of the Mu family: (1) MuA2 cosegregates with a genetically defined element that regulates somatic mutability of the a1-Mum2 allele; (2) MuA2 is hypomethylated while most other MuA2-hybridizing sequences in the genome are extensively methylated; (3) the increase of the copy number of MuA2 is concomitant with the increase of regulator elements; (4) MuA2-like elements are found in Mutator lines but not in non-Mutator inbreds. We propose that autonomous or transposase-encoding elements of the Mu family may be structurally conserved and MuA2-like.

Alleles↗
PubMed1994

Similar origins of two mouse minisatellites within transposon-like LTRs.

Tandem arrays of simple sequence repeat units are among the most unstable regions of mammalian genomes. Mutational instability at such loci depends on both repeat unit sequence and DNA sequences external to the tandem array, which have been recently implicated in polarized variability at human minisatellites. The characteristics of DNA sequences flanking the mouse minisatellite Ms6-hm have been investigated. This locus has a high mutation rate both in the germline and during early somatic development and is composed of a hypervariable tandem array of 500-2000 pentanucleotide repeat units flanked by a transposon-like long terminal repeat sequence of the mouse transcript (MT) family. A subpopulation of MT elements in the mouse genome are shown to flank a 1.1-kb internal sequence, consistent with their classification within a newly defined mammalian retrotransposon-like superfamily (MaLR). A second mouse minisatellite, Hm-2, also originates from within a MaLR LTR. Hm-2 is related to Ms6-hm in repeat unit sequence and profiles of germline and somatic instability; at both loci the tandem array has amplified from precisely the same point within the LTR. The similar origins of Ms6-hm and Hm-2 suggest that flanking MaLR sequences may be involved in mutational processes at these loci.

Animals↗
PubMed2004

Verification of somatic CAG repeat expansion by pre-PCR fractionation.

The inheritance of a long CAG repeat causes several late onset neurological disorders including Huntington's disease (HD). Longer CAG repeats correlate with earlier onset of HD suggesting an increased toxicity for the products of long repeat alleles. PCR based data has been used to show that HD CAG repeat expansion beyond the inherited length occurs in affected tissues indicating a possible role for somatic instability in the disease process. PCR, however, is prone to artifacts resulting from expansion of repeat sequences during amplification. We describe a method to distinguish between CAG repeat expansions that exist in vivo and those that potentially occur during PCR. The method involves size fractionation of genomic restriction fragments containing the expanded repeats followed by PCR amplification. The application of this method confirms the presence of somatic expansions in the brains of a knock-in mouse model of HD.

Animals↗
PubMed1995

Microsatellite instability in prostate cancer.

Assessment of the genetic instability of a microsatellite has indicated a new mechanism in human carcinogenesis. Examination was made to determine whether microsatellite instability is associated with the onset of prostate cancer. Twenty-nine DNA samples from 24 primary prostate cancer, two metastatic lymph-node and three benign prostatic hypertrophy patients were used. Differences in unrelated microsatellites for tumor and normal DNA were detected in nine of 24 (37.5%) cases. Seven of 11 (63.6%) with poorly differentiated adenocarcinomas and seven of 15 (46.7%) stage D metastatic patients showed somatic instability in a number of microsatellites. Statistically significant differences in well to moderately differentiated tumors and poorly differentiated cancer (P = 0.015, Chi-square test), were detected but not for stages A-C and D (P = 0.2311). Genetic alterations would thus appear to be rare in low grade and/or early prostate cancers but more common in high grade and/or advanced prostate cancers.

DNA Replication↗
PubMed1989

Molecular cloning of a maize gene involved in photosynthetic membrane organization that is regulated by Robertson's Mutator.

The maize photosynthetic mutant hcf106 has a distinctive and unusual thylakoid membrane organization, and fails to accumulate three of the five thylakoid membrane protein complexes. This mutant arose in a Robertson's Mutator background, and shows somatic instability typical of a transposon-induced allele. In addition, hcf106 is suppressed when Mu1 elements are inactive and modified in their terminal inverted repeats. Thus plants homozygous for the mutant allele adopt a mutant phenotype only when Mu1 elements are active and unmodified. DNA from the mutant allele has been cloned by 'transposon-tagging' using the transposon Mu1, and the identity of the clone confirmed by observing somatic excision of the transposon in a revertant sector. A 1.2 kb transcript homologous to the cloned DNA is found in wild-type and suppressed seedlings, but is not found in mutant seedlings, suggesting that suppression is mediated at the level of transcript accumulation.

Alleles↗
PubMedDate not supplied

Monitoring genomic alterations with a panel of oligonucleotide probes specific for various simple repeat motifs.

Germline and somatic instability of the human genome was studied, using synthetic oligonucleotides specific for simple repeat motifs. The following probes were used: (GTG)5, (GACA)4, (GATA)4, (CT)8, (TTAGGG)3, (GT)8, (GAA)6 and (GGAT)4. Each of them is unique with respect to the target regions recognized in the genome. Thus compilation of the various fingerprint data provides a complex map of the genome (and its deviations). While the fingerprints of differentiated somatic tissues never showed any alterations, in tumor tissues (namely gliomas) many changes could be detected. Most of the latter reflect secondary karyological aberrations. In nearly one third of the gliomas, drastically amplified and apparently monomorphic DNA fragments were identified. This marker should make it possible to deal with causal pathogenetic mechanisms as well as novel diagnostic strategies.

Base Sequence↗
PubMed1987

Heritable somatic excision of a Drosophila transposon.

A mutation in the white gene of Drosophila mauritiana that results from insertion of the transposable element mariner is genetically unstable in both germ cells and somatic cells. Somatic instability is indicated by the occurrence of animals having mosaic eyes with patches of pigmented cells on a peach-colored background. Normally uncommon, the frequency of mosaicism is so greatly enhanced in a particular mutant strain that virtually every animal in the strain is an eye-color mosaic. The molecular basis of the mosaicism is the excision of the mariner element from its location in the DNA of the white gene in somatic cells. The phenomenon results from a single dominant genetic factor located in chromosome 3. Genetic control over the excision of transposable elements may play a role in determining the persistence of transposable elements in the genome.

Alleles↗
PubMed1992

Moderate instability of the trinucleotide repeat in spino bulbar muscular atrophy.

Increased length of a protein-coding CAG repeat within the androgen receptor gene appears to be the only type of mutation responsible for spino-bulbal muscular atrophy (SBMA or Kennedy disease). We have analysed a large 4-generation SBMA family and found that the mutant allele was unstable upon transmission from parent to child, with a documented variation from 46 to 53 repeats and a tendency to increase in size (7 increases and a single decrease in 17 events), which appeared stronger upon transmission from a male than from a female. Our results suggest also limited somatic instability of the abnormal allele, with observable variation of up to 2-3 repeats. This indicates that the behavior of the CAG repeat is similar to that observed for small premutations in the fragile X syndrome, or small abnormal alleles in myotonic dystrophy, two diseases which are caused by expansion of an unstable trinucleotide repeat.

Alleles↗
PubMed2005

Dominant male sterility in sorghum: effect of nuclear background on inheritance of tissue-culture-induced mutation.

Occurrence of genetic instability and formation of stable mutations are basic genetic processes. This study demonstrates that nuclear background may influence the formation of stable dominant nuclear gene of male sterility (MS) on the basis of unstable mutation, which was induced in tissue culture of the sorghum haploid (cv. Milo-145). The mutants with complete or partial MS segregated in variable ratios in the progenies of diploid regenerants were obtained from different experiments on cultivation of haploid tissues. In the Milo-145 genetic background the mutation demonstrated somatic instability and was gradually eliminated by self-pollination of partially sterile plants. Hybridization of the MS-plants with the sorghum line SK-723, a fertility-restorer of the cytoplasmic MS A1 (milo) type, maintained the induced mutation. By repeated backcrossing of MS-plants with SK-723, the male-sterile versions of this line (SK-723- Ms(tc)) have been created. In BC-generations, fertile, partially and completely sterile plants were observed. The MS-plants from BC-generations are proposed to contain a dominant gene Ms(tc) while fertile plants were ms(tc)/ms(tc) homozygotes. Crossing the original MS-plants with SK-723 was a key factor in stabilization of the Ms(tc) gene. Dominant expression of the Ms(tc) was observed in male-sterile versions of other sorghum lines created by backcrossing to SK-723- Ms(tc). The lines fertility-restorers for this mutation have been revealed. In the crosses of restored F1 hybrids with emasculated plants of the non-restoring line, the Ms(tc) has been transferred through the pollen and manifested in the F1 generation. The possibility of the Ms(tc) originating as a result of interaction of an unstable allele of the Milo-145 with the SK-723 genome is discussed.

Breeding↗
PubMed1993

Stable expression of a single-copy rolA gene in transgenic Arabidopsis thaliana plants allows an exhaustive mutagenic analysis of the transgene-associated phenotype.

Several publications have documented the instability of transgene expression in plants. Previous genetic approaches to the study of transgene-associated phenotypes in plants were limited by this phenomenon. Here we show that a transgene can be expressed in plants with sufficient stability to allow an exhaustive mutagenic analysis of the resulting phenotype. We have expressed the morphogenic rolA gene from the TL-DNA of Agrobacterium rhizogenes Ri plasmid in transgenic Arabidopsis thaliana plants. The resulting pleiotropic RolA phenotype allows a visual screen for reversion to detect germinal as well as somatic instability of transgene expression. However no spontaneous reversions of the Ro-1A phenotype were observed in 65,000 progeny of two independent transgenic A. thaliana lines, each carrying a single homozygous rolA locus. In contrast, 12 revertants of the RolA phenotype were isolated from 360,000 ethyl methane sulphonate (EMS)-mutagenized M2 progeny. All revertants were shown genetically to carry stable recessive mutations in the rolA locus, thus establishing a series of loss-of-function alleles. Molecular characterization revealed that the loss-of-function alleles were structurally intact and expressed in all rolA mutants. A wildtype rolA locus and two loss-of-function alleles were reisolated and sequenced; base pair substitutions were found in each loss-of-function allele leading to single amino acid substitutions in the rolA open reading frame. Therefore no instability of expression of the rolA locus was detected in any of the 425,000 individuals studied in this analysis. Furthermore even under conditions of saturation mutagenesis, no extragenic suppressor locus was detected.

Amino Acid Sequence↗
PubMed1997

Tetra- and pentanucleotide short tandem repeat instability in gastric cancer.

The association between genetic instability in repetitive DNA domains and cancer has been reported in different types of malignancies. In this work we perform a comparative study of 29 gastric tumors with paired normal tissue using seven tetra-(FES/FPS, VWA31/A, HTPO, TH01, MBPB) and pentanucleotide (CD4, TP53) STR polymorphic markers regarding loss of heterozygosity and replication error status. Furthermore, we compare the gene frequencies obtained in normal tissue from patients with those of a normal control population from the same area, looking for allele associations between any of these polymorphic loci and gastric cancer risk. The results have shown that FES/FPS and TP53 present the higher rates of somatic instability. The observed results for TP53 are in accordance with those previously reported in gastric carcinogenesis, while instability of FES/FPS is for the first time reported in this tumor type. Our data suggest that different loci show different rates of instability and/or loss of heterozygosity and do not seem to consist of a result of an RER+ phenotype affecting several genomic repetitive domains. Furthermore, the instability in markers TH01, MBPB, TP53, and FES was generally detected in genotypes involving alleles with a high number of repeats. Comparing gene frequencies in patients and normal controls, no significant differences were found, although longer alleles are consistently more frequent in patients for the markers MBPB, TH01, and CD4.

Alleles↗
PubMed1989

Developmental and genetic aspects of Mutator excision in maize.

The regulation of excision of Mu elements of the Mutator transposable element family of maize is not well understood. We have used somatic instability of Mu receptor elements from the Bronze 1 and Bronze 2 loci to monitor the frequency and the timing of excision of Mu elements in several tissues. We show that spot size in the aleurone of a bz2::mu1 stock varies between one to approximately 256 cells. This indicates that excision events begin eight divisions prior to full aleurone differentiation and end after the last division of the aleurone. We show that excision is equally biased for late events in all other tissues studied. A locus on chromosome 5 has been identified that affects spot size, possibly by altering the timing of Mu excision. Using somatic excision as an assay of Mutator activity, we found that activity can change in small sectors of the tassel; however, there are no overall activity changes in the tassel during the period of pollen shedding. We also report the recovery of germinal revertants for the bz1::mu1 and bz2::mu1 alleles. One of these revertant alleles was characterized by Southern blot analysis and found to be similar to the progenitor of the mutable allele.

Alleles↗
PubMed1992

Constitutional ring chromosomes and tumour suppressor genes.

The types of malignancy reported in carriers of constitutional ring chromosomes r(11), r(13), and r(22) are concordant with the chromosomal assignment of tumour suppressor loci associated with Wilms' tumour, retinoblastoma, and meningioma. It is suggested that the somatic instability of ring chromosomes may play a role in this association and that constitutional ring chromosomes may be a source for mapping of tumour suppressor loci with the potential for covering most or all of the human genome. The hypothesis predicts the presence of a locus on chromosome 10 associated with follicular carcinoma of the thyroid, in line with previous cytogenetic findings of rearrangements involving chromosome 10 in thyroid tumours, and a locus on chromosome 22 associated with testicular cancer. Development of neurofibromatoses (NF) that do not fulfil the clinical criteria of neurofibromatosis type 2 (NF2) in carriers with r(22) suggests either the presence of an additional NF locus on chromosome 22 or that ring chromosome mediated predisposition to somatic mutation of a specific tumour suppressor may be associated with atypical development of features usually associated with germline mutations.

Adenocarcinoma↗
PubMed1998

Unusual mutations in high functioning fragile X males: apparent instability of expanded unmethylated CGG repeats.

We report on further cases of high functioning fragile X males showing decreased expression of FMR1 protein, absence of detectable methylation at the EagI site in the FMR1 gene promoter, and highly unusual patterns of fragile X mutations defined as smear of expansions extending from premutation to full mutation range. Very diffuse and therefore not easily detectable patterns of full mutations were also observed on prenatal testing using DNA from chorionic villi sampled at a time of development when full mutations were still unmethylated in this particular tissue. In the search for possible determinants of such unusual patterns, repeat expansions in the premutation and in the lower full mutation range were identified on genomic PstI blots previously prepared for fragile X DNA testing. Cases with 130 or more triplets, and a number of shorter repeats, were reinvestigated on EcoRI plus EagI digests. Among the 119 expansions, there were 22 in our sample showing either blurred bands or smears on PstI blots. This particular characteristic was strongly associated with the coincidence of a repeat size of more than 130 triplets and absence of EagI site methylation. Our data set also includes cases of mosaic patterns consisting of smears of unmethylated expansions to more than 130 CGGs and of clear bands of methylated expansions. We therefore suggest that in fragile X syndrome unusual smeared patterns of mutations result from somatic instability of larger repeats under circumstantial absence of repeat methylation.

Blotting, Southern↗