The mouse neurotrophin receptor trkB gene is transcribed from two different promoters

We have analysed a 7-kb region upstream of the mouse trkB coding sequence. The region showed promoter activity in transient transfection experiments a nd conferred tissue-specific expression to a reporter gene. Deletion analys is of this region demonstrated the presence of two alternative promoters na med P1 and P2 that have been mapped by RNase protection. P1 has been locate d to 1.8 kb and P2 to 0.5 kb upstream of the trkB translation start site. F rom the P1 promoter, alternative splicing generates various transcripts. In terestingly, P2 is located in an intron of the transcripts produced from th e PI promoter. This peculiar arrangement results in different mRNA species that encode the same protein(s) but differ in their 5'-untranslated regions . In addition, transcription of the trkB locus results in two different trk B isoforms (kinase and truncated receptors) originated by alternative splic ing of the mRNA, that possess differential spatial and temporal expression patterns. Using RT-PCR, we demonstrated that there was no linkage between p romoter usage and alternative splicing, since transcripts initiated from ea ch promoter encoded both kinase and truncated receptor proteins. (C) 1999 E lsevier Science B.V. All rights reserved.