Teleost paired fins are composed of two endoskeletal domains, proximal and distal radials, and an exoskeletal domain, the fin ray. The zebrafish pectoral fin displays elaborately patterned radials along the anteroposterior (AP) axis. Radials are considered homologous to tetrapod limb skeletons, and their patterning mechanisms in embryonic development are similar to those of limb development. Nevertheless, the pattern along the AP axis in fin rays has not been well described in the zebrafish pectoral fin, although several recent reports have revealed that fin ray development shares some cellular and genetic properties with fin/limb endoskeleton development. Thus, fin ray morphogenesis may involve developmental mechanisms for AP patterning in the fin/limb endoskeleton, and may have a specific pattern along the AP axis. We conducted detailed morphological observations on fin rays and their connection to distal radials by comparing intra- and inter-strain zebrafish specimens. Although the number of fin rays varied, pectoral fin rays could be categorized into three domains along the AP axis, according to the connection between the fin rays and distal radials; additionally, the number of fin rays varied in the posterior part of the three domains. This result was confirmed by observation of the morphogenesis process of fin rays and distal radials, which showed altered localization of distal radials in the middle domain. We also evaluated the expression pattern of lhx genes, which have AP patterning activity in limb development, in fin rays and during distal radial development and found these genes to be expressed during morphogenesis in both fin rays and distal radials. The fin ray and its connection to the endoskeleton are patterned along the AP axis, and the pattern along the AP axis in the fin ray and the radial connection is constructed by the developmental mechanism related to AP patterning in the limb/fin bud. Our results indicate the possibility that the developmental mechanisms of fin rays and their connection are comparable to those of the distal element of the limb skeleton.

中文翻译：

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基于与远端桡骨的连接，沿前后轴的鳍条射线模式

硬骨鱼成对的鳍由两个内骨骼域（近端和远端桡骨）和一个外骨骼域（鳍条）组成。斑马鱼胸鳍沿前后 (AP) 轴显示精心设计的放射状。桡骨被认为与四足肢体骨骼同源，它们在胚胎发育中的模式化机制与肢体发育相似。然而，斑马鱼胸鳍中沿 AP 轴的模式尚未在斑马鱼胸鳍中得到很好的描述，尽管最近的几份报告表明，鳍条的发育与鳍/肢内骨骼发育具有一些细胞和遗传特性。因此，鳍射线形态发生可能涉及鳍/肢体内骨骼中 AP 模式的发育机制，并且可能具有沿 AP 轴的特定模式。我们通过比较菌株内和菌株间斑马鱼标本，对鳍射线及其与远端径向的联系进行了详细的形态学观察。尽管鳍条的数量各不相同，但根据鳍条与远端桡骨之间的联系，胸鳍条可沿 AP 轴分为三个区域；此外，三个域后部的鳍条数量不同。通过观察鳍条和远端桡骨的形态发生过程证实了这一结果，这表明远端桡骨在中间区域的定位发生了改变。我们还评估了 lhx 基因的表达模式，这些基因在肢体发育中具有 AP 模式活性，在鳍条和远端桡骨发育过程中，发现这些基因在鳍条和远端桡骨的形态发生过程中表达。鳍条及其与内骨骼的连接沿 AP 轴形成图案，而鳍条中沿 AP 轴的图案和径向连接是由肢体/鳍芽中与 AP 图案相关的发育机制构建的。我们的研究结果表明，鳍条的发育机制及其连接可能与肢体骨骼远端元件的发育机制相当。