Ahmed Mohi U, Cheng Louise, Dietrich Susanne
Department of Craniofacial Development, King's College London, Guy's Hospital, London Bridge, London, United Kingdom.
Dev Dyn. 2006 Jul;235(7):1884-94. doi: 10.1002/dvdy.20832.
Trunk skeletal muscles are segregated into dorsomedial epaxial and ventrolateral hypaxial muscles, separated by a myoseptum. In amniotes, they are generated from a transient structure, the dermomyotome, which lays down muscle, namely the myotome underneath. However, the dermomyotome and myotome are dorsoventrally continuous, with no morphologically defined epaxial-hypaxial boundary. The transcription factors En1 and Sim1 have been shown to molecularly subdivide the amniote dermomyotome, with En1 labeling the epaxial dermomyotome and Sim1 the hypaxial counterpart. Here, we demonstrate that En1 and Sim1 expression persists in cells leaving the dermomyotome, superimposing the expression boundary onto muscle and skin. En1-expressing cells colonize the myotome initially from the rostral and caudal lips, and slightly later, directly from the de-epithelializing dermomyotomal center. En1 expression in the myotome is concomitant with the appearance of Fgfr4/Pax7-expressing mitotically active myoblasts. This finding suggests that Fgfr4+/Pax7+/En1+ cells carry their expression with them when entering the myotome. Furthermore, it suggests that the epaxial-hypaxial boundary of the myotome is established through the late arising, mitotically active myoblasts.
躯干骨骼肌被分隔为背内侧轴上肌和腹外侧轴下肌，中间由肌隔分隔。在羊膜动物中，它们由一个临时结构——皮肌节产生，皮肌节下方形成肌肉，即肌节。然而，皮肌节和肌节在背腹侧是连续的，没有形态学上明确的轴上-轴下边界。转录因子En1和Sim1已被证明在分子水平上对羊膜动物的皮肌节进行细分，En1标记轴上皮肌节，Sim1标记轴下皮肌节。在这里，我们证明En1和Sim1的表达在离开皮肌节的细胞中持续存在，将表达边界叠加到肌肉和皮肤上。表达En1的细胞最初从吻侧和尾侧唇区定殖到肌节，稍晚些时候，直接从正在去上皮化的皮肌节中心定殖到肌节。肌节中En1的表达与表达Fgfr4/Pax7的有丝分裂活跃的成肌细胞的出现同时发生。这一发现表明，Fgfr4+/Pax7+/En1+细胞在进入肌节时携带其表达。此外，这表明肌节的轴上-轴下边界是通过后期出现的、有丝分裂活跃的成肌细胞建立的。
