Characterizing exons 11 and 1 promoters of the mu opioid receptor (Oprm) gene in transgenic mice

Abstract

Background: The complexity of the mouse mu opioid receptor (Oprm) gene was demonstrated by the identification of multiple alternatively spliced variants and promoters. Our previous studies have identified a novel promoter, exon II (EII) promoter, in the mouse Oprm gene. The EII promoter is located ∼10 kb upstream of the exon I (EI) promoter. The EII promoter controls the expression of nine splice variants in the mouse Oprm gene. Distinguished from the TATA-less EI promoter, the EII promoter resembles a typical TATA-containing eukaryote class II promoter. The aim of this study is to further characterize the EII and EI promoters in vivo using a transgenic mouse model. Results: We constructed a ∼20 kb transgenic construct in which a 3.7 kb EII promoter region and an 8.9 kb EI promoter region controlled expression of tau/LacZ and tau/GFP reporters, respectively. The construct was used to establish a transgenic mouse line. The expression of the reporter mRNAs, determined by a RT-PCR approach, in the transgenic mice during embryonic development displayed a temporal pattern similar to that of the endogenous promoters. X-gal staining for tau/LacZ reporter and GFP imaging for tau/GFP reporter showed that the transgenic EII and EI promoters were widely expressed in various regions of the central nervous system (CNS). The distribution of tau/GFP reporter in the CNS was similar to that of MOR-I-like immunoreactivity using an exon 4-specific antibody. However, differential expression of both promoters was observed in some CNS regions such as the hippocampus and substantia nigra, suggesting that the EII and EI promoters were regulated differently in these regions. Conclusion: We have generated a transgenic mouse line to study the EII and EI promoters in vivo using tau/LacZ and tau/GFP reporters. The reasonable relevance of the transgenic model was demonstrated by the temporal and spatial expression of the transgenes as compared to those of the endogenous transcripts. We believe that these transgenic mice will provide a useful model for further characterizing the EII and EI promoter in vivo under different physiological and pathological circumstances such as chronic opioid treatment and chronic pain models. © 2006 Xu et al; licensee BioMed Central Ltd.