The Developmental and Physiological Consequences of Disrupting Genes Encoding β1 and β2 Adrenoceptors

Abstract

Publisher Summary The role that individual β AR subtypes play in specific physiological processes has been traditionally defined using subtype-specific ligands. Unfortunately, many of these ligands either possess poor selectivity or are used at concentrations in vivo that can lead to occupation of nonspecific subtypes. The advent of gene disruption techniques in the mouse now enables to selectively delete or alter cloned genes as a means of identifying the specific function(s) of their gene products. To better understand β AR subtype-specific functions in the context of either the whole animal or isolated organs and cells, the genes encoding both β 1 - and β 2 ARs have been disrupted. Gene targeting vectors containing β 1 AR or β 2 AR gene sequences interrupted or partially replaced by a bacterial neomycin resistance gene cassette were flanked by a viral thymidine kinase gene cassette. A standard positive-negative selection strategy (G418 + gancyclovir) has been used to isolate R1 embryonic stem (ES) cells, having undergone homologous recombination at β 1 AR or β 2 AR loci. The pharmacological profile of β 1 AR and β 2 AR knockouts is consistent with the loss of these specific receptor subtypes. When the nonspecific β AR antagonist [ 125 I]cyanopindolol is used in competition binding studies, excess unlabeled CGP 20712A ( β 1 AR-specific antagonist) reveals a selective loss of specific high-affinity sites in β 1 AR knockout heart or lung membranes while excess unlabeled ICI 118,551 ( β 2 AR-specific antagonist) reveals a selective loss of specific high-affinity sites in β 2 AR knockout lung membranes. These results provide further evidence that the β 1 AR and β 2 AR gene disruptions have abolished β AR protein expression. The physiological impact of knocking out either β 1 - or β 2 ARs has been studied in instrumented animals and in isolated tissues.