Regulatory characterisation of the novel gene, myocyte stress 1

Myocyte stress 1 (ms1) is a striated muscle actin binding protein required for muscle specific activity of the myocardin related transcription factor (MRTF)/serum response factor (SRF) transcriptional pathway. Previous work in our group demostrated that cardiac ms1 is transiently up-regulated after pressure overload suggesting a possible role in the initial signalling of the hypertrophic response. Subsequent studies have supported this and demonstrated that ms1 plays an important role in cardiac development and physiology. To date, little is known about the molecular mechanisms that govern striated muscle specific expression of ms1. In order to delineate ms1 regulation and function, a strategy of comparative in silico analysis coupled with experimental characterisation was used. In silico analysis identified four genomic intervals of potential regulatory function designated PP, UP1, UP2 and UP3. Using in vitro and in vivo appraoches, important cardiac regulatory roles for these domains were defined. The PP domain represents the basal promoter and is required for all regulatory contexts. This domain serves to intergrate context specific regulatory signals from the distal UP2 and UP3 domains. Within the heart the cardiac transcription factor GATA4, and the calcineurin singalling pathway confer cardiac regulatory function on the PP, UP2 and UP3 domains. Within skeletal muscle, MyoD binding sites within the PP and UP1 domain were identified, which mediate temporal induction of ms1 during myogenesis. Both cardiac and skeletal regulatory processes were dependent on epigenetic phenomena with histone acetylation being a major determinant for ms1 expression. Collectively, these findings demonstrate that ms1 transcriptional regulation is mediated by the complex interplay of context specific regulatory domains and binding factors. Therefore through ms1, important striated muscle gene regulatory networks (GRNs) (GATA4, Mef2 and MyoD GRNs) can integrate with SRF, thus exquisitely controlling biological processes in muscle. It is proposed that dysregulation of ms1 expression may result in pathological phenotypes. Therefore, the insights obtained here may allow for the therapeutic manipulation of ms1 expression in pathological settings and potentially lead to effective paliatation of such phenotypes.