Department of Genetics, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts, USA.
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, USA.
Dev Dyn. 2021 Sep;250(9):1264-1279. doi: 10.1002/dvdy.308. Epub 2021 Feb 15.
Before limbs or fins, can be patterned and grow they must be initiated. Initiation of the limb first involves designating a portion of lateral plate mesoderm along the flank as the site of the future limb. Following specification, a myriad of cellular and molecular events interact to generate a bud that will grow and form the limb. The past three decades has provided a wealth of understanding on how those events generate the limb bud and how variations in them result in different limb forms. Comparatively, much less attention has been given to the earliest steps of limb formation and what impacts altering the position and initiation of the limb have had on evolution. Here, we first review the processes and pathways involved in these two phases of limb initiation, as determined from amniote model systems. We then broaden our scope to examine how variation in the limb initiation module has contributed to biological diversity in amniotes. Finally, we review what is known about limb initiation in fish and amphibians, and consider what mechanisms are conserved across vertebrates.
在肢体或鳍出现之前，它们必须先被启动。肢体的启动首先涉及到指定沿体侧的侧板中胚层的一部分作为未来肢体的位置。在指定之后，无数的细胞和分子事件相互作用，产生一个将生长并形成肢体的芽。在过去的三十年中，人们对这些事件如何产生肢体芽以及它们的变化如何导致不同的肢体形式有了丰富的了解。相比之下，人们对肢体形成的最早步骤以及改变肢体的位置和启动对进化的影响关注较少。在这里，我们首先回顾了从羊膜动物模型系统中确定的这两个肢体启动阶段所涉及的过程和途径。然后，我们扩大范围，研究肢体启动模块的变化如何为羊膜动物的生物多样性做出贡献。最后，我们回顾了鱼类和两栖类动物肢体启动的相关知识，并考虑了哪些机制在脊椎动物中是保守的。
