McGurk Patrick D, Swartz Mary E, Chen Jessica W, Galloway Jenna L, Eberhart Johann K
Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, United States of America.
Center for Regenerative Medicine, Harvard Stem Cell Institute, Department of Orthopaedic Surgery, Massachusetts General Hospital, Boston, MA, United States of America.
PLoS Genet. 2017 Dec 11;13(12):e1007112. doi: 10.1371/journal.pgen.1007112. eCollection 2017 Dec.
Integrated development of diverse tissues gives rise to a functional, mobile vertebrate musculoskeletal system. However, the genetics and cellular interactions that drive the integration of muscle, tendon, and skeleton are poorly understood. In the vertebrate head, neural crest cells, from which cranial tendons derive, pattern developing muscles just as tendons have been shown to in limb and trunk tissue, yet the mechanisms of this patterning are unknown. From a forward genetic screen, we determined that cyp26b1 is critical for musculoskeletal integration in the ventral pharyngeal arches, particularly in the mandibulohyoid junction where first and second arch muscles interconnect. Using time-lapse confocal analyses, we detail musculoskeletal integration in wild-type and cyp26b1 mutant zebrafish. In wild-type fish, tenoblasts are present in apposition to elongating muscles and condense in discrete muscle attachment sites. In the absence of cyp26b1, tenoblasts are generated in normal numbers but fail to condense into nascent tendons within the ventral arches and, subsequently, muscles project into ectopic locales. These ectopic muscle fibers eventually associate with ectopic tendon marker expression. Genetic mosaic analysis demonstrates that neural crest cells require Cyp26b1 function for proper musculoskeletal development. Using an inhibitor, we find that Cyp26 function is required in a short time window that overlaps the dynamic window of tenoblast condensation. However, cyp26b1 expression is largely restricted to regions between tenoblast condensations during this time. Our results suggest that degradation of RA by this previously undescribed population of neural crest cells is critical to promote condensation of adjacent scxa-expressing tenoblasts and that these condensations are subsequently required for proper musculoskeletal integration.
多种组织的整合发育产生了一个功能完备、可移动的脊椎动物肌肉骨骼系统。然而，驱动肌肉、肌腱和骨骼整合的遗传学和细胞间相互作用仍知之甚少。在脊椎动物头部，颅神经嵴细胞是颅部肌腱的来源，它们对发育中的肌肉进行模式化，就像在肢体和躯干组织中肌腱所表现的那样，但这种模式化的机制尚不清楚。通过正向遗传学筛选，我们确定cyp26b1对腹侧咽弓的肌肉骨骼整合至关重要，特别是在第一和第二弓肌肉相互连接的下颌舌骨连接处。使用延时共聚焦分析，我们详细研究了野生型和cyp26b1突变斑马鱼的肌肉骨骼整合情况。在野生型鱼中，成腱细胞与伸长的肌肉并列存在，并在离散的肌肉附着部位聚集。在缺乏cyp26b1的情况下，成腱细胞数量正常产生，但未能在腹侧弓内聚集成新生肌腱，随后，肌肉伸入异位区域。这些异位肌纤维最终与异位肌腱标记物表达相关联。遗传镶嵌分析表明，神经嵴细胞需要Cyp26b1功能才能实现正常的肌肉骨骼发育。使用一种抑制剂，我们发现Cyp26功能在与成腱细胞聚集的动态窗口重叠的短时间窗口内是必需的。然而，在此期间，cyp26b1的表达主要局限于成腱细胞聚集之间的区域。我们的结果表明，这群先前未描述的神经嵴细胞对视黄酸的降解对于促进相邻表达scxa的成腱细胞的聚集至关重要，并且这些聚集随后是正常肌肉骨骼整合所必需的。
