The bovine α2D-adrenergic receptor gene:: Structure, expression in retina, and pharmacological characterization of the encoded receptor

This report describes cloning of the bovine alpha(2D)-adrenergic receptor (alpha(2D)-AR) gene and determination of the transcription start site, unequivocal presence of the alpha(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 lambda 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 alpha(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 alpha(2D)-AR, but, the highest homology was observed with the porcine receptor expressing alpha(2A)-AR pharmacological characteristics. Certain structural features of the bovine gene were unique to itself and not shared by any other alpha(2)-AR subtype. Among the tissues tested using reverse transcriptase-polymerase chain reaction (RT-PCR), the alpha(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 alpha(2D)-AR physiology in neurosensory processes such as those occurring in the eye and the brain.