Functional expression of the type 1 inositol 1,4,5-trisphosphate receptor promoter-lacZ fusion genes in transgenic mice

Inositol 1,4,5-trisphosphate receptor (IP₃R) is an inositol 1,4,5- trisphosphate (InsP₃)-gated Ca²⁺ release channel. Type 1 IP₃R (IP₃R1) is the neuronal member of the IP₃R family in the CNS and is predominantly expressed in cerebellar Purkinje cells. To elucidate the molecular mechanisms responsible for coupling gene expression to neuronal InsP₃/Ca²⁺ signaling, we have studied the structure and function of the 5'-flanking region of the mouse IP₃R1 gene. The cloned 5'-flanking region has several sequences sharing identity with motifs for known transcriptional regulation. We have fused 5'-flanking regions 1N from -528 to +169 and 4N from -4,187 to +169 to a β-galactosidase gene (lacZ) as a reporter marker and have characterized their in vivo gene expression. Both 1N and 4N fusion genes functioned as a strong promoter in a neuroblastoma-glioma hybrid cell line NG108-15. Moreover, both 1N and 4N transgenic mouse lines carrying these 1N and 4N fusion genes showed characteristic patterns of β-galactosidase activity in the CNS that are almost consistent with that of the endogenous IP₃R1 protein, thereby suggesting that the 1N region from -528 to + 169 contains sequence elements responsible for regulating gene expression in neurons and for specifying predominant expression in cerebellar Purkinje cells.