Characterization of tissue-specific transcription by the human synapsin I gene promoter

Synapsin Ia and synapsin Ib are abundant synaptic vesicle proteins that are derived by differential splicing from a single gene. To identify control elements directing the neuronal expression of synapsins Ia/b, we functionally analyzed the promoter region of the human synapsin I gene. A hybrid gene was constructed containing 2 kilobases of 5' flanking sequence from the synapsin I gene fused to the bacterial gene chloramphenicol acetyltransferase and transfected into 12 different neuronal and nonneuronal cell lines. In general, expression of the chimeric reporter gene showed excellent correlation with endogenous expression of synapsin I in different neuronal cell lines, whereas transcription was low in all nonneuronal cell lines examined. The addition of the simian virus 40 enhancer promoted non-tissue-specific expression. Deletion mutagenesis of the synapsin I promoter revealed the presence of positive and negative sequence elements. A basal (constitutive) promoter that directs reporter gene expression in neuronal and nonneuronal cell lines was mapped to the region -115 to +47. The promoter region from -422 to -22 contains positive elements that upon fusion with the herpes simplex virus thymidine kinase promoter potentiate its transcription in PC12 and neuroblastoma cells but not in Chinese hamster ovary cells.