The bovine α(2D)-adrenergic receptor gene: Structure, expression in retina, and pharmacological characterization of the encoded receptor

This report describes cloning of the bovine α(2D)-adrenergic receptor (α(2D)-AR) gene and determination of the transcription start site, unequivocal presence of the α(2D)-AR transcript in the retina, and pharmacological characteristics of the encoded product. Furthermore, expression of the gene in selected bovine tissues has also been scrutinized. A genomic clone was isolated from λ. EMBL3 library and a 3 kb fragment was subcloned and sequenced. This fragment contained the putative TATA box and the coding region. The encoded receptor was transiently expressed in COS cells. The recombinant receptor expressed pharmacological characteristics almost identical to the wild-type bovine retinal receptor, which were typical of the α(2D)-AR subtype. RNase protection analysis confirmed the expression of the gene in the retina. The bovine receptor was structurally close to its rat analogue which also encodes the α(2D)-AR, but, the highest homology was observed with the porcine receptor expressing α(2A)-AR pharmacological characteristics. Certain structural features of the bovine gene were unique to itself and not shared by any other α₂-AR subtype. Among the tissues tested using reverse transcriptase-polymerase chain reaction (RT-PCR), the α(2D)-AR message was the most abundant in retina, followed by the brain and olfactory lobe. Thus, the availability of the bovine receptor gene probe will become an important additional tool in the elucidation of molecular mechanisms behind the α(2D)-AR physiology in neurosensory processes such as those occurring in the eye and the brain.