G protein coupled receptors (GPCRs) represent the largest family of signalling molecules present in the organism and are found in all phyla from viruses through yeast to mammals. This sequence diversity is reflected in their expression patterns which invariably show that each transcript has a unique distribution. As anticipated, this diversity of gene type and distribution is most manifest in the CNS. This poses both problems and opportunities. On the one hand, such unique distributions offer potential for highly specific therapeutic targets. On the other hand, they present a problem of phenotypic regulation: How are these expression patterns established and maintained? It is this latter aspect that is the focus of this review.
Establishment of mature phenotype typically, but not always, occurs around the time of differentiation and represents activation of programmes of gene transcription. Maintenance, by contrast, occurs throughout the life of the organism and may involve both transcriptional and post-transcriptional mechanisms. Mechanisms responsible for establishment and maintenance of transcription may be quite distinct. As a primer, the following section presents a brief overview of these processes.
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