Dealy C N
Department of Anatomy, University of Connecticut Health Center, Farmington, Connecticut 06030, USA.
Dev Biol. 1997 Aug 15;188(2):216-23. doi: 10.1006/dbio.1997.8646.
Acquisition of limb-forming ability by discrete regions of the lateral plate of the chick embryo is thought to depend on a signaling cascade moving sequentially from the area of Hensen's node to the somitic mesoderm, the intermediate mesoderm, and then to the prospective limb-forming regions of the lateral plate (Stephens et al., 1991). In the present study it is demonstrated that grafts of Hensen's node can induce the formation of supernumerary rudimentary limbs from the non-limb-forming flank region of the lateral plate of stage 9-15 chick embryos. The rudimentary limbs that form from the flank in response to Hensen's node grafts often contain elongated, jointed cartilaginous elements arranged in three distinct proximodistal segments resembling the developing stylopod, zeugopod, and autopod and express the limb-characteristic genes Msx-2 and BMP-4. However, the rudimentary limbs are incomplete and nonpolarized in that they do not form girdles or paired skeletal elements and fail to express sonic hedgehog, FGF-4, and FGF-8, signaling molecules that have been implicated in regulating the patterning of the developing limb bud. These results indicate that Hensen's node can provide a limb-forming signal to the lateral mesoderm, but that other signals are necessary to promote the expression of genes required for the complete patterning and morphogenesis of the limb.
鸡胚侧板离散区域获得肢体形成能力被认为依赖于一个信号级联反应，该反应依次从亨森氏结区域传至体节中胚层、中间中胚层，然后到达侧板的预期肢体形成区域（斯蒂芬斯等人，1991年）。在本研究中，已证明将亨森氏结移植到9-15期鸡胚侧板的非肢体形成侧腹区域，能够诱导额外的雏形肢体形成。响应亨森氏结移植而从侧腹形成的雏形肢体通常包含细长的、有关节的软骨元件，这些元件排列成三个不同的近远节段，类似于正在发育的肱骨、桡尺骨和手足骨，并表达肢体特征基因Msx-2和BMP-4。然而，这些雏形肢体并不完整且无极化，因为它们不形成带骨或成对的骨骼元件，并且无法表达音猬因子、FGF-4和FGF-8，这些信号分子被认为与调节发育中的肢体芽的模式形成有关。这些结果表明，亨森氏结可以向外侧中胚层提供肢体形成信号，但还需要其他信号来促进肢体完全模式形成和形态发生所需基因的表达。
