The human homolog of murine Evi-2 lies between two von Recklinghausen neurofibromatosis translocations

Von Recklinghausen neurofibromatosis (NF1) is one of the most common inherited human disorders. The genetic locus that harbors the mutation(s) responsible for NF1 is near the centromere of chromosome 17, within band q11.2. Translocation breakpoints that have been found in this region in two patients with NF1 provide physical landmarks and suggest an approach to identifying the NF1 gene. As part of our exploration of this region, we have mapped the human homolog of a murine gene (Evi-2) implicated in myeloid tumors to a location between the two translocation breakpoints on chromosome 17. Cosmid-walk clones define a 60-kb region between the two NF1 translocation breakpoints. The probable role of Evi-2 in murine neoplastic disease and the map location of the human homolog suggest a potential role for EVI2 in NF1, but no physical rearrangements of this gene locus are apparent in 87 NF1 patients.     

Deletions and a translocation interrupt a cloned gene at the neurofibromatosis type 1 locus.

Three new neurofibromatosis type 1 (NF1) mutations have been detected and characterized. Pulsed-field gel and Southern blot analyses reveal the mutations to be deletions of 190, 40, and 11 kb of DNA. The 11 kb deletion does not contain any of the previously characterized genes that lie between two NF1 translocation breakpoints, but it does include a portion of a rodent/human conserved DNA sequence previously shown to span one of the translocation breakpoints. By screening cDNA libraries with the conserved sequence, we identified a number of cDNA clones from the translocation breakpoint region (TBR), one of which hybridizes to an approximately 11 kb mRNA. The TBR gene crosses at least one of the chromosome 17 translocation breakpoints found in NF1 patients. Furthermore, the newly characterized NF1 deletions remove internal exons of the TBR gene. Although these mutations might act by compromising regulatory elements affecting some other gene, these findings strongly suggest that the TBR gene is the NF1 gene.     

Fine structure DNA mapping studies of the chromosomal region harboring the genetic defect in neurofibromatosis type 1

To better map the location of the von Recklinghausen neurofibromatosis (NF1) gene, we have characterized a somatic cell hybrid designated 7AE-11. This microcell-mediated, chromosome-transfer construct harbors a centromeric segment and a neo-marked segment from the distal long arm of human chromosome 17. We have identified 269 cosmid clones with human sequences from a 7AE-11 library and, using a panel of somatic cell hybrids with a total of six chromosome 17q breakpoints, have mapped 240 of these clones on chromosome 17q. The panel included a hybrid (NF13) carrying a der(22) chromosome that was isolated from an NF1 patient with a balanced translocation, t(17;22) (q11.2;q11.2). Fifty-three of the cosmids map into a region spanning the NF13 breakpoint, as defined by the two closest flanking breakpoints (17q11.2 and 17q11.2-q12). RFLP clones from a subset of these cosmids have been mapped by linkage analysis in normal reference families, to localize the NF1 gene more precisely and to enhance the potential for genetic diagnosis of this disorder. The cosmids in the NF1 region will be an important resource for testing DNA blots of large-fragment restriction-enzyme digests from NF1 patient cell lines, to detect rearrangements in patients' DNA and to identify the 17;22 NF1 translocation breakpoint.