Skeletal muscle hypotrophy and precocious differentiation in Ddx27 deficiency.

<p>(A-B) Histology of longitudinal skeletal muscle sections in control and <i>ddx27</i> mutant stained with toluidine blue exhibiting enlarged nucleoli (arrowhead) and areas lacking sarcomeres (arrow) at 5 dpf. High magnification view (boxed area) (C-G) Transmission electron micrographs of skeletal muscles (longitudinal view: C-E, and cross-section view: F-G) in control and <i>ddx27</i> mutant (5 dpf). Arrows indicating disorganized sarcomere (H) Quantification of myofiber size in control and <i>ddx27</i> mutant fish (5 dpf) (n = 10) (I) qRT-PCR of control and <i>ddx27</i> mutant fish showed a reduction in the expression of muscle stem cell markers (<i>pax3</i>, <i>pax7</i>) and an increase in expression of myogenic commitment genes (<i>myod1</i> and <i>myf5</i>). The expression of late differentiation markers was reduced in <i>ddx27</i> fish suggesting that pre-mature expression of early myogenic genes results in abnormal disorganization of skeletal muscles.