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J F Gusella

Publications and source records attributed to J F Gusella.

At least 37 records · Page 2Linked to original sources
PubMed1999

Merlin: the neurofibromatosis 2 tumor suppressor.

In recent years, it has become clear that the ERMs occupy a crucial position as protein linkers that both respond to and participate in reorganization of membrane-cytoskeletal interactions. With the identification of new binding partners, the ERMs are also implicated in linked regulation of the activities of particular membrane proteins. Thus, they reside at a junction in a complex web of interactions that must respond to stimuli from both outside and inside the cell. As expected from its structural motifs, merlin behaves in a manner similar to the ERM proteins, but with some notable differences. Chief among these is the absence of intramolecular interaction to mask intermolecular interaction domains in isoform 2. The full range of merlin's intermolecular interactions remains to be delineated, but it can be expected from the comparison to ERMs that merlin also sits within a web of interactions that may involve multiple partners and signaling pathways, some of which it shares with the ERMs. Defining merlin's tumor suppressor function will likely require identifying those differences that are peculiarly important in the target cell types of NF2. However, the fact that inactivation of merlin in the mouse by targeted mutagenesis produces a variety of malignant tumors with a high rate of metastasis [33] suggests that merlin's suppression of tumor formation may involve different partners and pathways in different cell types and genetic backgrounds. Consequently, the disruptions due to merlin inactivation in the progression of malignant mesothelioma may represent a tumor suppressor role operating by a different pathway than that in schwannoma or meningioma.

DNA Mutational Analysis↗
PubMed1999

Mutant huntingtin forms in vivo complexes with distinct context-dependent conformations of the polyglutamine segment.

Huntington's disease (HD) is caused by an expanded glutamine tract, which confers a novel aggregation-promoting property on the 350-kDa huntingtin protein. Using specific antibodies, we have probed the structure of the polyglutamine segment in mutant huntingtin complexes formed in cell culture from either truncated or full-length protein. Complexes formed by a mutant amino terminal fragment most frequently entail a change in conformation that eliminates reactivity with the polyglutamine-specific mAb 1F8, coincident with production of insoluble aggregate. By contrast, complexes formed by the full-length mutant protein remain soluble and are invariably 1F8-reactive, indicating a soluble polyglutamine conformation. Therefore, aggregates in HD may form by different biochemical mechanisms that invoke different possibilities for the pathogenic process. If pathogenesis is triggered by a truncated fragment, it probably involves the formation of an insoluble aggregate. However, the observation of soluble complexes in which an HD-specific pathogenic conformation of the glutamine tract remains accessible suggests that pathogenesis could also be triggered at the level of full-length huntingtin by abnormal aggregation with normal or abnormal protein partners.

Animals↗
PubMed1999

Allelic expression of the NF2 gene in neurofibromatosis 2 and schwannomatosis.

Neurofibromatosis type 2 (NF2) is a genetic disorder characterized by formation of multiple schwannomas and meningiomas due to inactivating mutations in the NF2 tumor suppressor gene on chromosome 22. We describe a polymorphism in the 3' untranslated region of the NF2 gene that is informative in about one-third of individuals. This polymorphism permitted an assessment of the relative expression of NF2 transcripts in lymphoblastoid cell RNA from 22 unrelated NF2 patients heterozygous for a germline NF2 mutation, along with 6 schwannomatosis patients, and 14 unaffected controls. Unequal allelic expression (1.8- to 20-fold) was detected in 15 of the NF2 cases, but in none of the schwannomatosis or control individuals. Underexpression of the NF2 mutant allele was documented for all 6 nonsense or frameshift mutations, 3 of 6 splice mutations, and 1 of 4 missense mutations, which, unexpectedly, was shown to alter the NF2 transcript and create a premature stop codon. In contrast, equal expression or slight overexpression of NF2 mutant alleles was observed for 2 in-frame deletions, 2 splice alterations, and 3 missense mutations. In the remaining 5 cases, the allele representing the mutant transcript was not known. Thus, truncating NF2 mutations, which are the most frequent alterations in NF2 patients and NF2-associated tumors, were associated with underexpression of the mutant allele, whereas the less common in-frame alterations usually showed normal or slight overexpression of the mutant transcript.

Alleles↗
PubMed1999

Mapping of a target region of allelic loss to a 0.5-cM interval on chromosome 22q13 in human colorectal cancer.

BACKGROUND & AIMS: Chromosomal allelic losses have a varying frequency in colorectal cancer. The aim of this study was to define the target region of allelic loss on chromosome 22q in human colorectal carcinogenesis. METHODS: Fifty-seven pairs of matched normal colonic mucosa and tumor specimens from patients with colorectal cancer, as well as 15 colon cancer-derived cell lines, were genotyped using 15 microsatellite markers spanning chromosome 22q. A potential candidate gene was analyzed by a single-strand conformation polymorphism (SSCP)/direct DNA sequencing approach. RESULTS: After excluding 7 tumors with evidence of microsatellite instability, allelic loss was observed in 11 of the informative tumors (22%), 5 of which exhibited losses in all informative loci. The remaining 6 tumors showed variable patterns of partial allelic loss on chromosome 22q, thereby localizing a minimal region of allelic deletion between markers D22S1171 and D22S928. Physical mapping showed that this interval was 0.57 cM consisting of approximately 425 kilobases. Database searches identified the NBK/BIK gene, a proapoptotic BCL-2 family member, as a candidate gene in that region. However, SSCP/sequencing analysis excluded mutations of this gene. CONCLUSIONS: This study provides evidence for the involvement of putative tumor-suppressor gene(s) on chromosome 22q in human colorectal carcinogenesis. The identification of a 0.5-cM interval serves as the basis for the isolation of such a gene by positional cloning.

Alleles↗
PubMed1999

Precise genetic mapping and haplotype analysis of the familial dysautonomia gene on human chromosome 9q31.

Familial dysautonomia (FD) is an autosomal recessive disorder characterized by developmental arrest in the sensory and autonomic nervous systems and by Ashkenazi Jewish ancestry. We previously had mapped the defective gene (DYS) to an 11-cM segment of chromosome 9q31-33, flanked by D9S53 and D9S105. By using 11 new polymorphic loci, we now have narrowed the location of DYS to <0.5 cM between the markers 43B1GAGT and 157A3. Two markers in this interval, 164D1 and D9S1677, show no recombination with the disease. Haplotype analysis confirmed this candidate region and revealed a major haplotype shared by 435 of 441 FD chromosomes, indicating a striking founder effect. Three other haplotypes, found on the remaining 6 FD chromosomes, might represent independent mutations. The frequency of the major FD haplotype in the Ashkenazim (5 in 324 control chromosomes) was consistent with the estimated DYS carrier frequency of 1 in 32, and none of the four haplotypes associated with FD was observed on 492 non-FD chromosomes from obligatory carriers. It is now possible to provide accurate genetic testing both for families with FD and for carriers, on the basis of close flanking markers and the capacity to identify >98% of FD chromosomes by their haplotype.

Alleles↗
PubMed1999

Mapping of the mucolipidosis type IV gene to chromosome 19p and definition of founder haplotypes.

Mucolipidosis type IV (MLIV) is a lysosomal storage disorder characterized by severe neurologic and ophthalmologic abnormalities. It is a rare autosomal recessive disease, and the majority of patients diagnosed, to date, are of Ashkenazi Jewish descent. We have mapped the MLIV gene to chromosome 19p13.2-13.3 by linkage analysis with 15 markers in 13 families. A maximum LOD score of 5.51 with no recombinants was observed with marker D19S873. Several markers in the linked interval also displayed significant linkage disequilibrium with the disorder. We constructed haplotypes in 26 Ashkenazi Jewish families and demonstrate the existence of two founder chromosomes in this population. The localization of MLIV to chromosome 19 will permit genetic prenatal diagnosis in affected families and will aid in the isolation of the disease gene.

Chromosome Mapping↗
PubMed1999

Length-dependent gametic CAG repeat instability in the Huntington's disease knock-in mouse.

The CAG repeats in the human Huntington's disease (HD) gene exhibit striking length-dependent intergenerational instability, typically small size increases or decreases of one to a few CAGs, but little variation in somatic tissues. In a subset of male transmissions, larger size increases occur to produce extreme HD alleles that display somatic instability and cause juvenile onset of the disorder. Initial efforts to reproduce these features in a mouse model transgenic for HD exon 1 with 48 CAG repeats revealed only mild intergenerational instability ( approximately 2% of meioses). A similar pattern was obtained when this repeat was inserted into exon 1 of the mouse Hdh gene. However, lengthening the repeats in Hdh to 90 and 109 units produced a graded increase in the mutation frequency to >70%, with instability being more evident in female transmissions. No large jumps in CAG length were detected in either male or female transmissions. Instead, size changes were modest increases and decreases, with expansions typically emanating from males and contractions from females. Limited CAG variation in the somatic tissues gave way to marked mosaicism in liver and striatum for the longest repeats in older mice. These results indicate that gametogenesis is the primary source of inherited instability in the Hdh knock-in mouse, as it is in man, but that the underlying repeat length-dependent mechanism, which may or may not be related in the two species, operates at higher CAG numbers. Moreover, the large CAG repeat increases seen in a subset of male HD transmissions are not reproduced in the mouse, suggesting that these arise by a different fundamental mechanism than the small size fluctuations that are frequent during gametogenesis in both species.

Age Factors↗
PubMed1999

Analysis of germline mutation spectra at the Huntington's disease locus supports a mitotic mutation mechanism.

Trinucleotide repeat disease alleles can undergo 'dynamic' mutations in which repeat number may change when a gene is transmitted from parent to offspring. By typing >3500 sperm, we determined the size distribution of Huntington's disease (HD) germline mutations produced by 26 individuals from the Venezuelan cohort with CAG/CTG repeat numbers ranging from 37 to 62. Both the mutation frequency and mean change in allele size increased with increasing somatic repeat number. The mutation frequencies averaged 82% and, for individuals with at least 50 repeats, 98%. The extraordinarily high mutation frequency levels are most consistent with a mutation process that occurs throughout germline mitotic divisions, rather than resulting from a single meiotic event. In several cases, the mean change in repeat number differed significantly among individuals with similar somatic allele sizes. This individual variation could not be attributed to age in a simple way or to ' cis ' sequences, suggesting the influence of genetic background or other factors. A familial effect is suggested in one family where both the father and son gave highly unusual spectra compared with other individuals matched for age and repeat number. A statistical model based on incomplete processing of Okazaki fragments during DNA replication was found to provide an excellent fit to the data but variation in parameter values among individuals suggests that the molecular mechanism might be more complex.

Adolescent↗
PubMed1999

Clonal analysis of a case of multiple meningiomas using multiple molecular genetic approaches: pathology case report.

OBJECTIVE: Multiple meningiomas are uncommon brain tumors occurring concurrently in several intracranial locations in the same patient. In the present study, we determined the clonality, methylation status of deoxyribonucleic acid, and relationship of genetic alterations in eight meningiomas from one female patient. METHODS: Six molecular genetic techniques, including two methylation-based clonality assays and one transcription-based clonality assay, methylation analysis of CpG islands by methylation-specific polymerase chain reaction, loss of heterozygosity, microsatellite instability, and mutational analysis of the NF2 gene on chromosome 22, were used in comparative investigations on clonality and genetic alterations. RESULTS: The presence of clonal tumor cells was demonstrated by 1) loss of the same copy of chromosome 22 in all eight tumors; 2) transcription of the human AR gene from the same allele in six of eight tumors; 3) a common unmethylated allele at the AR locus in all eight tumors; and 4) the identical single-basepair insertion mutation in exon 9 of the NF2 gene in six of eight tumors. In addition, loss of a copy of the X chromosome in one tumor nodule and microsatellite instability in another nodule were observed. CONCLUSION: Taken together, this case of multiple meningiomas was most likely monoclonal in origin. Loss of chromosome 22 was an early event during the development of multiple meningiomas and was followed by mutations at the NF2 locus. Later events, including loss of the X chromosome, variation of AR gene expression, or microsatellite instability, may also have played a role in the development of multiple meningiomas in this patient.

Brain↗
PubMed1998

A single nucleotide polymorphism in the matrix metalloproteinase-1 promoter creates an Ets binding site and augments transcription.

Matrix metalloproteinases (MMPs) facilitate cellular invasion by degrading the extracellular matrix, and their regulation is partially dependent on transcription. Binding sites for members of the Ets family of transcription factors are present within MMP promoters and are potent positive regulators. We report a single nucleotide polymorphism at -1607 bp in the MMP-1 promoter, where an additional guanine (G) creates an Ets binding site, 5'-GGA-3'. This polymorphism displays significantly higher transcription in normal fibroblasts and in melanoma cells than the 1 G polymorphism, and it binds substantially more nuclear extract and recombinant ETS-1. Analysis of control DNAs from the Center d'Etude du Polymorphisme Humain pedigrees reveals that this polymorphism is not a mutation, with a frequency of the 2 G polymorphism at 30%. In contrast, in eight tumor cell lines, this frequency increased to 62.5% (P < 0.0001). Thus, this MMP-1 polymorphism contributes to increased transcription, and cells expressing the 2 G polymorphism may provide a mechanism for more aggressive matrix degradation, thereby facilitating cancer progression.

Binding Sites↗
PubMed1998

Mice heterozygous for a mutation at the Nf2 tumor suppressor locus develop a range of highly metastatic tumors.

A role for the membrane/cytoskeleton interface in the development and progression of cancer is established, yet poorly understood. The neurofibromatosis type II (NF2) tumor suppressor gene encodes a member of the ezrin/radixin/moesin (ERM) family of membrane/cytoskeleton linker proteins thought to be important for cell adhesion and motility. We report that in contrast to the narrow spectrum of benign tumors in human NF2 patients, Nf2 heterozygous mice develop a variety of malignant tumors. Using the fact that Nf2 is linked to the p53 tumor suppressor locus in the mouse we have also investigated the effects of genetic linkage of cancer-predisposing mutations on tumorigenesis and examined the genetic pathway to tumor formation involving Nf2 loss. Importantly, we observed a very high rate of metastasis associated with Nf2 deficiency, with or without loss of p53 function, and we provide experimental evidence supporting a role for Nf2 loss in metastatic potential. Together, our results suggest an important role for the NF2 tumor suppressor, and perhaps the ERM family in tumor formation and metastasis.

Animals↗
PubMed1998

Huntingtin: a single bait hooks many species.

Cloning of the Huntington's disease gene uncovered huntingtin, which is remarkable for its lack of similarity with known proteins despite its large size, approximately 350 kDa. Subsequent experiments established that huntingtin has an as yet unknown function, crucial for embryonic development and neurogenesis. Recent protein trapping to identify huntingtin interactors now reveals that many different prey fall victim to huntingtin bait.

Animals↗
PubMed1998

Genetic variation in the 3' untranslated region of the neurofibromatosis 1 gene: application to unequal allelic expression.

Neurofibromatosis type 1 (NF1) is a common genetic disorder caused by inactivation of neurofibromin, a protein capable of modulating signal transduction by activating Ras-GTPase activity. We have used cDNA cloning and Northern blot analysis to confirm the NF1 gene produces alternatively polyadenylated mRNAs with 3' untranslated regions (3' UTR) that show striking evolutionary conservation. Scanning of the 3'UTRs for genetic variation revealed three common sequence polymorphisms (> 30% heterozygosity), one less informative polymorphism (approximately 5% heterozygosity) and one rare variant (1/144 chromosomes). These differences were used to examine relative levels of expression of normal and mutant NF1 alleles in lymphoblast cell lines and in one case, autopsy tissue, from patients with NF1. Unequal allelic expression (up to 4-fold) was observed in a subset of both sporadic and familial NF1 cases. Where linkage phase could be determined, the allele segregating with the disorder displayed a relative reduction in expression. However, the magnitude of this effect was variable suggesting the operation of additional, non-genetic factors in determining the degree of relative expression of the mutant allele.

3' Untranslated Regions↗
PubMed1998

Amyloid formation by mutant huntingtin: threshold, progressivity and recruitment of normal polyglutamine proteins.

Huntington's disease (HD) is caused by an expanded CAG trinucleotide repeat encoding a tract of consecutive glutamines near the amino terminus of huntingtin, a large protein of unknown function. It has been proposed that the expanded polyglutamine stretch confers a new property on huntingtin and thereby causes cell and region-specific neurodegeneration. Genotype-phenotype correlations predict that this novel property appears above a threshold length (approximately 38 glutamines), becomes progressively more evident with increasing polyglutamine length, is completely dominant over normal huntingtin and is not appreciably worsened by a double genetic dose in HD homozygotes. Recently, an amino terminal fragment of mutant huntingtin has been found to form self-initiated fibrillar aggregates in vitro. We have tested the capacity for aggregation to assess whether this property matches the criteria expected for a fundamental role in HD pathogenesis. We find that that in vitro aggregation displays a threshold and progressivity for polyglutamine length remarkably similar to the HD disease process. Moreover, the mutant huntingtin amino terminus is capable of recruiting into aggregates normal glutamine tract proteins, such as the amino terminal segments of both normal huntingtin and of TATA-binding protein (TBP). Our examination of in vivo aggregates from HD post-mortem brains indicates that they contain an amino terminal segment of huntingtin of between 179 and 595 residues. They also contain non-huntingtin protein, as evidenced by immunostaining for TBP. Interestingly, like the in vitro aggregates, aggregates from HD brain display Congo red staining with green birefringence characteristic of amyloid. Our data support the view that the expanded polyglutamine segment confers on huntingtin a new property that plays a determining role in HD pathogenesis and could be a target for treatment. Moreover, the new property might have its toxic consequences by interaction with one or more normal polyglutamine-containing proteins essential for the survival of target neurons.

Adult↗