Cheng Louise, Alvares Lúcia E, Ahmed Mohi U, El-Hanfy Amira S, Dietrich Susanne
Department of Craniofacial Development, King's College London, London Bridge, London SE1 9RT, UK.
Dev Biol. 2004 Oct 15;274(2):348-69. doi: 10.1016/j.ydbio.2004.07.020.
In all jaw-bearing vertebrates, three-dimensional mobility relies on segregated, separately innervated epaxial and hypaxial skeletal muscles. In amniotes, these muscles form from the morphologically continuous dermomyotome and myotome, whose epaxial-hypaxial subdivision and hence the formation of distinct epaxial-hypaxial muscles is not understood. Here we show that En1 expression labels a central subdomain of the avian dermomyotome, medially abutting the expression domain of the lead-lateral or hypaxial marker Sim1. En1 expression is maintained when cells from the En1-positive dermomyotome enter the myotome and dermatome, thereby superimposing the En1-Sim1 expression boundary onto the developing musculature and dermis. En1 cells originate from the dorsomedial edge of the somite. Their development is under positive control by notochord and floor plate (Shh), dorsal neural tube (Wnt1) and surface ectoderm (Wnt1-like signalling activity) but negatively regulated by the lateral plate mesoderm (BMP4). This dependence on epaxial signals and suppression by hypaxial signals places En1 into the epaxial somitic programme. Consequently, the En1-Sim1 expression boundary marks the epaxial-hypaxial dermomyotomal or myotomal boundary. In cell aggregation assays, En1- and Sim1-expressing cells sort out, suggesting that the En1-Sim1 expression boundary may represent a true compartment boundary, foreshadowing the epaxial-hypaxial segregation of muscle.
在所有具有颌骨的脊椎动物中,三维运动依赖于分离的、分别受神经支配的轴上肌和轴下骨骼肌。在羊膜动物中,这些肌肉由形态上连续的皮肌节和肌节形成,其轴上 - 轴下细分以及由此形成不同的轴上 - 轴下肌肉的机制尚不清楚。在这里,我们表明En1表达标记了鸟类皮肌节的一个中央亚域,内侧邻接领先的外侧或轴下标记物Sim1的表达域。当来自En1阳性皮肌节的细胞进入肌节和皮节时,En1表达得以维持,从而将En1 - Sim1表达边界叠加到发育中的肌肉组织和真皮上。En1细胞起源于体节的背内侧边缘。它们的发育受脊索和底板(Shh)、背侧神经管(Wnt1)和表面外胚层(Wnt1样信号活性)的正向控制,但受侧板中胚层(BMP4)的负向调节。这种对轴上信号的依赖和轴下信号的抑制使En1进入轴上体节程序。因此,En1 - Sim1表达边界标志着轴上 - 轴下皮肌节或肌节边界。在细胞聚集试验中,表达En1和Sim1的细胞会分选出来,这表明En1 - Sim1表达边界可能代表一个真正的分隔边界,预示着肌肉的轴上 - 轴下分离。