Changes in appendage structure underlie key transitions in vertebrate evolution. Addition of skeletal elements along the proximal-distal axis facilitated critical transformations, including the fin-to-limb transition that permitted generation of diverse modes of locomotion. Here, we identify zebrafish mutants that form supernumerary long bones in their pectoral fins. These new bones integrate into musculature, form joints, and articulate with neighboring elements. This phenotype is caused by activating mutations in previously unrecognized regulators of appendage patterning, vav2 and waslb, that function in a common pathway. This pathway is required for appendage development across vertebrates, and loss of Wasl in mice causes defects similar to those seen in murine Hox mutants. Concordantly, formation of supernumerary bones requires Hox11 function, and mutations in the vav2/wasl pathway drive enhanced expression of hoxa11b, indicating developmental homology with the forearm. Our findings reveal a latent, limb-like pattern ability in fins that is activated by simple genetic perturbation.

附属物结构的变化是脊椎动物进化关键转变的基础。沿近端-远端轴添加骨骼元素促进了关键的转变，包括允许产生不同运动模式的鳍到肢的过渡。在这里，我们确定了在胸鳍中形成多余长骨的斑马鱼突变体。这些新骨骼融入肌肉组织，形成关节，并与相邻元素连接。这种表型是由以前未被识别的附属模式调节器vav2和waslb 中的激活突变引起的，它们在共同的途径中发挥作用。这条通路是脊椎动物的附属物发育和Wasl缺失所必需的在小鼠中引起的缺陷与在小鼠 Hox 突变体中看到的相似。一致地，形成额外的骨骼需要HOX11功能，并且突变的VAV2 / WASL通路驱动增强表达hoxa11b，指示与前臂发育的同源性。我们的研究结果揭示了鳍中一种潜在的、类似肢体的模式能力，这种能力是由简单的遗传扰动激活的。