Sequence analysis has shown significant homology between the catalytic regions of the mammalian ras GTPase-activating protein (GAP), yeast Ira1p and Ira2p (inhibitory regulators of the RAS-cyclic AMP pathway), and neurofibromin, the protein encoded by the NF1 gene. Yeast expression experiments have confirmed that a 381-amino-acid segment of neurofibromin, dubbed the GAP-related domain (GRD), can function as a GAP. Using the RNA polymerase chain reaction with primers flanking the NF1-GRD, we have identified evidence for alternative splicing in this region of the NF1 gene. In addition to the already published sequence (type I), an alternative RNA carrying a 63-nucleotide insertion (type II) is present in all tissues examined, although the relative amounts of types I and II vary. The insertion is conserved across species but is not present in GAP, IRA1, or IRA2. GenBank searches have failed to identify significant similarity between the inserted sequence and known DNA or protein sequences, although the basic amino acid composition of the insertion shares features with nuclear targeting sequences. Expression studies in yeasts show that despite the partial disruption of the neurofibromin-IRA-GAP homology by this insertion, both forms of the NF1-GRD can complement loss of IRA function. In vivo assays designed to compare the GAP activity of the two alternatively spliced forms of the NF1-GRD show that both can increase the conversion of GTP-bound ras to its GDP-bound form, although the insertion of the 21 amino acids weakens this effect. The strong conservation of this alternative splicing suggests that both type I and II isoforms mediate important biological functions of neurofibromin.

The gene for neurofibromatosis type 1 (NF1) was identified by positional cloning and found to contain two alternatively spliced exons. The first described alternatively spliced exon (exon 23a) is located within the GAP-related domain of the gene and inserts an additional 63 nucleotides into the NF1 mRNA. The second alternatively spliced exon (exon 48a) is located near the extreme carboxy terminus of the gene and inserts an additional 54 nucleotides into the mRNA. This second isoform, termed 3'ALT, was originally detected while screening a fetal brain cDNA library. Examination of its expression by reverse-transcribed RNA PCR demonstrates high level of expression in cardiac muscle, skeletal muscle and smooth muscle. Trace levels of expression are detected in brain and nerve. The 3'ALT isoform is expressed in fetal cardiac muscle, adult left ventricle and cardiac Purkinje cells. Further confirmation of the existence of this isoform was obtained by blotting the PCR products with a radiolabeled oligonucleotide entirely derived from sequences contained within exon 48a and by direct sequencing of the PCR products. Additionally, this isoform is expressed in muscle tissues from other vertebrate species. The expression of this isoform in muscle suggests that the NF1 gene may play additional tissue-specific roles in muscle development and signal transduction.

Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder characterized by progressive and variable involvement of tissues predominantly derived from the neural crest and a predisposition toward malignancies. The NF1 gene encodes neurofibromin, a GTPase-activating protein containing a GAP-related domain (NF1-GRD) that is capable of down-regulating ras by stimulating its intrinsic GTPase activity. We report a homozygous deletion of most of NF1 in one of eight malignant melanoma cell lines leading to loss of detectable mRNA and protein, as well as the apparent absence of protein and mRNA in another melanoma. This data suggests that NF1 can function as a tumour suppressor gene in the development or progression of malignant melanoma.

Journal Article A compound nucleotide repeat in the neurofibro-matosis (NF1) gene Get access Lone B. Andersen, Lone B. Andersen Howard Hughes Medical Institute, Departments of Human Genetics and Internal Medicine, The University of Michigan Medical CenterAnn Arbor, Ml 48109, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar Susan A. Tarlé, Susan A. Tarlé Howard Hughes Medical Institute, Departments of Human Genetics and Internal Medicine, The University of Michigan Medical CenterAnn Arbor, Ml 48109, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar Douglas A. Marchuk, Douglas A. Marchuk Howard Hughes Medical Institute, Departments of Human Genetics and Internal Medicine, The University of Michigan Medical CenterAnn Arbor, Ml 48109, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar Eric Legius, Eric Legius Howard Hughes Medical Institute, Departments of Human Genetics and Internal Medicine, The University of Michigan Medical CenterAnn Arbor, Ml 48109, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar Francis S. Collins Francis S. Collins * Howard Hughes Medical Institute, Departments of Human Genetics and Internal Medicine, The University of Michigan Medical CenterAnn Arbor, Ml 48109, USA *To whom correspondence should be addressed Search for other works by this author on: Oxford Academic PubMed Google Scholar Human Molecular Genetics, Volume 2, Issue 7, July 1993, Page 1083, https://doi.org/10.1093/hmg/2.7.1083-a Published: 01 July 1993

Journal Article A polymorphic cDNA probe on chromosome 17q11.2 located within the NF1 gene [D17S376] Get access L.B. Andersen, L.B. Andersen Search for other works by this author on: Oxford Academic PubMed Google Scholar M.R. Wallace, M.R. Wallace Search for other works by this author on: Oxford Academic PubMed Google Scholar D.A. Marchuk, D.A. Marchuk Search for other works by this author on: Oxford Academic PubMed Google Scholar R.M. Cawthon, R.M. Cawthon 1Howard Hughes Medical Institute, University of Utah Medical Center603 Wintrobe, Salt Lake City, UT 84132, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar H.M. Odeh, H.M. Odeh Search for other works by this author on: Oxford Academic PubMed Google Scholar R. Letcher, R. Letcher Search for other works by this author on: Oxford Academic PubMed Google Scholar R. LWhite, R. LWhite 1Howard Hughes Medical Institute, University of Utah Medical Center603 Wintrobe, Salt Lake City, UT 84132, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar F.S. Collins F.S. Collins * * To whom correspondence should be addressed Search for other works by this author on: Oxford Academic PubMed Google Scholar Nucleic Acids Research, Volume 19, Issue 1, 11 January 1991, Page 197, https://doi.org/10.1093/nar/19.1.197-a Published: 11 January 1991

The gene responsible for neurofibromatosis type 1 (NF1), one of the more common inherited human disorders, was identified recently, and segments of it were cloned. Two translocation breakpoints that interrupt the NF1 gene in NF1 patients flank a 60-kb segment of DNA that contains the EVI2A locus (previously reported as the EVI2 locus), the human homolog of a mouse gene, Evi-2A, implicated in retrovirus-induced murine myeloid tumors. EVI2A lies within an intron of the NF1 gene and is transcribed from telomere toward centromere, opposite to the direction of transcription of the NF1 gene. Here we describe a second locus, EVI2B, also located between the two NF1 translocation breakpoints. Full-length cDNAs from the EVI2B locus detect a 2.1-kb transcript in bone marrow, peripheral blood mononuclear cells, and fibroblasts. Sequencing studies predict an EVI2B protein of 448 amino acids that is proline-rich and contains an N-terminal signal peptide, an extracellular domain with four potential glycosylation sites, a single hydrophobic transmembrane domain, and a cytoplasmic hydrophilic domain. At the level of genomic DNA the EVI2B locus lies within the same intron of the NF1 gene as EVI2A and contains a 57-bp 5′ exon that is noncoding, an 8-kb intron, and a 2078-bp 3′ exon that includes the entire open reading frame. EVI2B is transcribed in the same direction as EVI2A; its 5′ exon lies only 4 kb downstream from the 3′ exon of the EVI2A locus. In the mouse the 5′ exon of the homologous gene, Evi-2B, lies approximately 2.8 kb from the 3′ end of Evi-2A, in the midst of a cluster of viral integration sites identified in retrovirus-induced myeloid tumors; thus, Evi-2B may function as an oncogene in these tumors.

Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder with a high mutation rate and variable expression, characterized by neurofibromas, café-au-lait spots, Lisch nodules of the iris, and less frequent features including bone deformities and learning disabilities. The recently cloned NF1 gene encodes a transcript of 13 kilobases from a ubiquitously expressed locus on chromosome 17. Most NF1 patients are expected to have unique mutations, but only a few have so far been characterized, restricting genetic and functional information and the design of DNA diagnostics. We report an unusual NF1 mutation, that of a de novo Alu repetitive element insertion into an intron, which results in deletion of the downstream exon during splicing and consequently shifts the reading frame. This previously undescribed mechanism of mutation indicates that Alu retrotransposition is an ongoing process in the human germ line.

A deletion of 90 kb of DNA has been identified in a patient with neurofibromatosis type 1, using pulsed field gel electrophoresis. The deletion lies between probes 17L1A and AC5 in the critical region of chromosome 17 and represents the only molecular alteration found by PFGE in a series of 90 unrelated patients. The subject showing the deletion is an isolated case, shows typical clinical features, and represents one of the first examples of a molecular deletion to be found in this disorder.

Von Recklinghausen neurofibromatosis (NF1) is a common autosomal dominant disorder characterized by abnormalities in multiple tissues derived from the neural crest. No reliable cellular phenotypic marker has been identified, which has hampered direct efforts to identify the gene. The chromosome location of the NF1 gene has been previously mapped genetically to 17q11.2, and data from two NF1 patients with balanced translocations in this region have further narrowed the candidate interval. The use of chromosome jumping and yeast artificial chromosome technology has now led to the identification of a large (∼13 kilobases) ubiquitously expressed transcript (denoted NF1LT ) from this region that is definitely interrupted by one and most likely by both translocations. Previously identified candidate genes, which failed to show abnormalities in NF1 patients, are apparently located within introns of NF1LT , on the antisense strand. A new mutation patient with NF1 has been identified with a de novo 0.5-kilobase insertion in the NF1LT gene. These observations, together with the high spontaneous mutation rate of NF1 (which is consistent with a large locus), suggest that NF1LT represents the elusive NF1 gene.

The von Recklinghausen neurofibromatosis ( NF1 ) gene has been previously localized to the region 17q11.2 by genetic analysis. Consistent with this, two NF1 patients have been described with autosomal translocations with breakpoints in 17q11.2, and these represent presumed markers for the location of the NF1 gene. Recent work has defined the two breakpoints on a physical map, and they lie less than 100 kb apart. To characterize further the distance between these breakpoints and clone additional DNA, a chromosome jump was made from a DNA fragment that maps between the breakpoints. The end of the jump crosses one of the NF1 translocation breakpoints and detects that breakpoint on Southern analysis, placing the probe less than 15 kb telomeric to this breakpoint. Pulsed field analysis with the jump clone allows revision of the previous NF1 region map and indicates that the two breakpoints lie no more than 60 kb apart. This jump clone will be useful for further mapping, breakpoint cloning, analysis of patient DNA, and the search for transcripts in the NF1 region.