Trans-synaptic control of NGFI-A and jun-B expression: Contrasting transcriptional and post-transcriptional mechanisms directed by common receptors

Previous studies have demonstrated that of the multiple primary response gene products which are induced in the rat pineal gland through a nocturnally activated adrenoceptor-linked mechanism, JunB is the principal component of a dark phase-specific activator protein-1 DNA binding complex. JunB is therefore implicated as a nuclear component of the mechanisms that determine nocturnal changes in pineal function. It is now shown that the marked increase in jun-B mRNA expression following norepinephrine stimulation in vitro, is mediated through a post-transcriptional mechanism that involves mRNA stabilization. This mode of regulation is contrasted with that controlling the expression of other primary response genes. In the case of NGFI-A, a co-regulated primary response gene which is controlled through a pharmacologically similar pathway, nuclear run-on transcription assays have shown that pineal mRNA levels are elevated through an increase in transcription rate that can be measured both in vitro and in vivo. These results show that multiple molecular mechanisms are engaged to effect the genomic consequences of adrenoceptor stimulation, and that rhythmic changes in gene expression may be controlled by post-transcriptional mechanisms involving mRNA stability.