Neurofibromatosis 1 ((NF1)) mRNAs expressed in the central nervous system are differentially spliced in the 5′ part of the gene

The neurofibromatosis 1 gene seems to play essential roles at several different stages of life. During embryogenesis, it is involved in cardiac development while in the adult, neurofibromin (the corresponding protein) is mainly expressed In the nervous system, and therein, essentially in neurons, non-myeiinating Schwann cells and ollgodendrocytes. In addition, the NF1 gene is considered a tumor suppressor gene, since mutations have been associated with the occurrence of benign and malignant tumors in neuralcrest-derived tissues. Using reverse transcription polymerase chain reaction (RT-PCR) analyses with primers located in exons 7 and 13, we have identified evidence of alternative splicing in this region of the NF1 gene. Cloning and sequencing of cDNA allowed the characterization of an isotorm bearing an extra 30 bp sequence between exons 9 and 10a, leading to the insertion of 10 amino acids between residues 420 and 421 of neurofibromin. The insertion is conserved in the mouse. Examination of the pattern of expres sion of this isoform demonstrated a high level of expression in the central nervous system and an absence of expression in all the other normal tissues tested including peripheral nervous tissues derived from the neural crest. Analysis of brain tumors indi cated a reduced expression of the alternative exon in meduiloblastomas and oligodendrogliomas. The results presented here are consistent with tissuespecific expression of this alternative exon which we propose to call exon 9br.