Insulin-like growth factor-I is an osmoprotectant in human neuroblastoma cells.

A role in neuronal homeostasis is suggested by the persistent expression of the insulin-like growth factors in the adult nervous system. SH-SY5Y human neuroblastoma cells, a well-characterized in vitro model of human neurons, were used to investigate the effects of hyperosmotic stress on neurons. Neuronal DNA fragmentation was detected within 1 h and pyknotic nuclei were apparent in attached cells after 12 h of hyperosmotic stress. In parallel, flow cytometry measurements revealed a sudden increase in the rate of cells irreversibly undergoing programmed cell death after 12 h of hyperosmotic exposure. Insulin-like growth factor-I delayed the onset of a laddered DNA fragmentation pattern for 24 h and provided continuing protection against hyperosmotic exposure for 72 h. Amino acid uptake was decreased in hyperosmotic medium even in the presence of insulin-like growth factor-I; the protein synthesis inhibitor cycloheximide neither prevented the induction of programmed cell death nor interfered with the ability of insulin-like growth factor-I to act as an osmoprotectant in hyperosmotic medium. Cysteine and serine protease inhibitors each prevented DNA fragmentation under hyperosmotic conditions, suggesting that the osmoprotectant activity of insulin-like growth factor-I involves the suppression of protease activity. Collectively, these results indicate that insulin-like growth factor-I limits the death of neurons under stressful environmental conditions, suggesting that it may provide a candidate therapy in the treatment of hyperosmolar coupled neurological injury.

A chromosome jump crosses a translocation breakpoint in the von Recklinghausen neurofibromatosis region.

The von Recklinghausen neurofibromatosis (NFI) gene has been previously localized to the region 17q11.2 by genetic analysis. Consistent with this, two NFI patients have been described with autosomal translocations with breakpoints in 17q11.2, and these represent presumed markers for the location of the NFI 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 NFI 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 NFI 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 NFI region.

Type 1 neurofibromatosis gene: identification of a large transcript disrupted in three NF1 patients.

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 (approximately 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.