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. Author manuscript; available in PMC: 2010 Nov 17.
Published in final edited form as: Dev Cell. 2009 Nov;17(5):662–673. doi: 10.1016/j.devcel.2009.10.013

Figure 8. Control of myosin and fast versus slow muscle gene expression by the MyomiR network.

Figure 8

In the adult heart, miR-208a encoded by the α-MHC gene is required for expression of β-MHC and Myh7b, which encode miR-208b and miR-499, respectively. Activation of Myh7b by miR-208a is constitutive, whereas activation of β-MHC also requires stress signals or absence of thyroid hormone. In slow skeletal muscle, Myh7b and β-MHC are regulated independently of miR-208a. miR-208a, -208b, and -499 repress the expression of a common set of transcriptional repressors that repress slow myosin and the slow myofiber gene program at the expense of fast muscle gene expression. Activation of the slow myofiber gene program also creates a positive feedback loop via the expression of miR-208b and miR-499, which further reinforce slow muscle gene program. Regulatory interactions within the blue box are shared by cardiac and slow skeletal muscle.