Region specific morphogenesis of the axial skeleton in avian embryos: tissue interactions and molecular mechanism

脊椎动物被认为是通过重复和修改节段单位来构建的。从根本上说，它的发育单位是体节。不仅骨骼和肌肉起源于体节，脊神经和交感干的发育也受到体节的控制。为了考虑脊椎动物的身体计划是如何建立的，我们研究了从体节到轴向骨骼的发育机制。特别是，我们的兴趣集中在肋骨的发育区域--特别是在禽类胚胎中。肋骨的三个发育隔室：体节与周围组织相互作用的观察表明，肋骨的近端小部分与脊椎连接(近端的肋骨)取决于脊索和神经管的底板，而除了近端的肋骨(远端的肋骨)的长的隔室取决于表面外胚层。此外，远端肋骨可分为两个PAR…更多的T。体节细胞从肋骨内关节远端的肋骨(胸骨远端肋骨)迁移到躯体胸膜，而没有进入躯体胸膜的体节细胞形成关节近端的一部分(脊椎远端肋骨)。它们分别属于远轴和原始上颌室，这是由Ann Burke最近提出的。远端肋骨形态发生和体节分化：在体节和表面外胚层之间插入薄膜以阻断它们之间的相互作用时，表达SIM1的皮肌节的外侧部分和表达硬化轴的皮肌节外围的硬化体细胞缺失。提示这些区域对肋骨远端发育具有支持作用。躯干体壁肌肉的区域特异性形态发生：腹肌的节段性单位。(1)命运图：腹肌大部分起源于第27节体节，第26节和第28节体节分别形成吻端和尾端区域。其他腰肌节形成肋骨或躯干体壁肌肉。(2)神经支配：成年母鸡和刚出生的鸡，腹肌主要由胸神经支配。由于腹肌的躯体起源和支配腹肌的脊神经沿嘴-尾轴的水平不同，神经支配并不总是能让我们了解肌肉的发育起源。肢体发育和肋骨发育：当我们在鸡胚胎的侧翼区域诱导肢体时，胸骨远端肋骨缺失。四肢和胸骨肋骨都属于背轴骨室，胚胎可能只允许发育其中之一。中轴骨骼原基的确定：我们将鹌鹑表皮或原始条纹异位移植到鸡胚中，检测HOX基因的表达和所形成的骨骼的形态，结果表明，在原肠形成之前，体细胞中胚层所在的上胚层部分被确定为某种类型的椎骨和/或肋骨。较少

Vertebrates are considered to be constructed by repeating and modifying segmental unit. Fundamentally, its developmental unit is somite. Not only the skeleton and muscles derived from somites, but also development of the spinal nerve and sympathetic trunk is under control of somites. To consider how the body plan is established in the vertebrate, we have investigated the mechanism of development from somites into the axial skeleton. Especially, our interest is focused on the development of the rib that develops region-specifically in the avian embryo.1. Three developmental compartment of the rib : Examination of interaction between the somites and their surrounding tissues showed that small proximal part of the rib articulating with the vertebra (proximal rib) develops depending on the notochord and the floor plate of neural tube, and long compartment other than the proximal rib (distal rib) develops depending on the surface ectoderm. Further, the distal rib can be divided into tow par … More ts. Somite cells migrate into the somatopleura form a part of the rib distal to the intra-rib articulation (sternal distal rib), while somite cells which do not enter the somatopleura form a part proximal to this joint (vertebral distal rib). These belong to the abaxial and primaxial compartment, respectively, which are recently proposed by Ann Burke.2. Distal rib morphogenesis and somite differentiation : When we inserted thin film between the somite and the surface ectoderm to block the interaction between them, lateral part of the dermomyotome expressing Sim1 and sclerotomal cells at the periphery of dermomyotome expressing Scleroaxis were missing. These regions are suggested to support the distal rib development.3. Region specific morphogenesis of trunk body wall muscles : Segmental unit of abdominal muscles.(1) Fate mapping: We showed that most part of the abdominal muscles was derived from the 27th somite and the 26th and the 28th somite formed the rostral and the caudal end region, respectively. Other lumbar somites form either the ribs or the trunk body wall muscles.(2) Innervations: In adult hen and chicken just after birth, we found that the abdominal muscles were largely innervated by the thoracic nerves. Because the somitic origin of abdominal muscles and the spinal nerve innervating them were from different levels along rostro-caudal axis, innervations will not always allow us to know the developmental origin of muscles.4. Limb development and rib development : When we induced a limb at the flank region in a chick embryo, the sternal distal ribs were missing. Both the limb and the sternal rib belong to the abaxial compartment and the embryo might allow to develop only one of them.5. Determination of the primordium of the axial skeleton : We transplanted heterotopically the quail epidermis or primitive streak into chick embryo and examined expression of Hox genes and morphology of resultant skeleton, showing that a part of epiblast where the somitic mesoderm arises was determined to become a certain type of vertebrae and/or ribs just before gastrulation. Less