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. Author manuscript; available in PMC: 2011 Aug 15.
Published in final edited form as: Dev Biol. 2010 Dec 11;350(2):464–475. doi: 10.1016/j.ydbio.2010.12.010

Figure 7. Model of Myod:Cdkn1c Positive Feedback.

Figure 7

Adaxial MRF expression initiates independent of Hedgehog (Hh) signals, through Fgf (1). Hh initiates cdkn1c expression (2) leading to gradual accumulation of Myod protein (3) that maintains cdkn1c expression (4), creating a positive feedback loop (5) that triggers muscle differentiation (6). A possible additional role of Cdkn1 is maintenance of cell cycle exit (7). A proliferative effect of Hh in myogenesis has been reported in mouse myoblasts and chick somite cells, as indicated by the dashed line (8). However, all available evidence argues against a proliferative effect of Hh in zebrafish myogenesis. Instead, Hh apparently independently maintains MRF mRNA in anterior PSM (9).