Transcriptional control of the m4 muscarinic receptor gene: mammalian and yeast models

The mammalian nervous system is comprised of approximately loio_1011 neurones, each of which has a potentially unique repertoire of expressed genes. The m4 muscarinic acetylcholine receptor gene has a very restricted pattern of expression within the nervous system, being expressed mainly in the autonomic ganglia and telencephalon. Using transient transfection assays in mammalian cell lines I show that the m4 gene is under the control of a constitutively active core-promoter which is selectively repressed in m4 non-expressing cells. This repression is mediated at least in part by the zinc finger repressor REST. Further, in the fibroblast cell line 3T3, I show that the m4 gene is expressed via two distinct promoters which are differentially regulated by REST. In order to dissect the molecular mechanisms that mediate REST repression I have expressed REST in yeast and shown it to be a potent repressor of the yeast GAL1 promoter. Further, characterisation of those regions of REST that are important for repression in yeast map to those regions that mediate repression in mammalian cells. This suggests that REST acts via mechanisms and molecules that are conserved through evolution between yeast and mammals. To identify genes important in mediating REST repression, I expressed REST in the absence of the yeast global repressors SSN6 and SIN3. Deletion of SSN6 had no effect on REST mediated repression while as deletion of SIN3 resulted in complete loss of repression by REST. These experiments show that the conserved gene SIN3 is essential for REST mediated repression in yeast and suggest that SIN3 may act as a co-repressor for REST in mammalian cells. The implications of REST repressing via SIN3 and future directions based in these findings are discussed.