Physiological regulation at the level of mRNA: Analysis of steady-state levels of specific mRNAs by DNA-excess solution hybridization

Recent appreciation for how systems may be regulated at the protein and mRNA levels has dictated that physiological questions be addressed at both. The application of novel and sensitive biochemical and molecular biological techniques may be necessary to answer questions fundamental to our understanding of physiological regulation. For measurements of low-abundance proteins, such as receptors for hormones and growth factors, and for measurement of their corresponding mRNAs, the need for highly sensitive assays is critical. The present work focuses both on recent studies of the regulation of steady-state levels of mRNAs and on how mRNAs are quantified by DNA-excess solution hybridization assays using highly specific single-stranded probes. Examples of physiological regulation are provided in which analysis of mRNA levels has been a key facet to our understanding of the mode of regulation. The construction and characterization of probes for solution hybridization assays are described using the hamster β₂-adrenergic receptor as a model. Studies on the regulation of β-adrenergic receptors by agonists and by permissive hormones as well as investigations on the regulation of apolipoproteins by estrogen and by cholesterol in vivo are used to illustrate the many advantages of analyzing the steady-state levels of specific mRNAs by DNA-excess solution hybridization.