Institute of Neuroscience, University of Oregon, Eugene, Oregon, USA.
Institute of Molecular Biology, University of Oregon, Eugene, Oregon, USA.
Dev Dyn. 2022 Aug;251(8):1306-1321. doi: 10.1002/dvdy.475. Epub 2022 Apr 22.
Caudal fin symmetry characterizes teleosts and likely contributes to their evolutionary success. However, the coordinated development and patterning of skeletal elements establishing external symmetry remains incompletely understood. We explore the spatiotemporal emergence of caudal skeletal elements in zebrafish to consider evolutionary and developmental origins of caudal fin symmetry.
Transgenic reporters and skeletal staining reveal that the hypural diastema-defining gap between hypurals 2 and 3 forms early and separates progenitors of two plates of connective tissue. Two sets of central principal rays (CPRs) synchronously, sequentially, and symmetrically emerge around the diastema. The two dorsal- and ventral-most rays (peripheral principal rays, PPRs) arise independently and earlier than adjacent CPRs. Muscle and tendon markers reveal that different muscles attach to CPR and PPR sets.
We propose that caudal fin symmetry originates from a central organizer that establishes the hypural diastema and bidirectionally patterns surrounding tissue into two plates of connective tissue and two mirrored sets of CPRs. Further, two peripheral organizers unidirectionally specify PPRs, forming a symmetric "composite" fin derived from three fields. Distinct CPR and PPR ontogenies may represent developmental modules conferring ray identities, muscle connections, and biomechanical properties. Our model contextualizes mechanistic studies of teleost fin morphological variation.
尾鳍对称性是硬骨鱼类的特征，可能有助于它们的进化成功。然而，建立外部对称性的骨骼元素的协调发育和模式仍然了解不完全。我们探索了斑马鱼尾部骨骼元素的时空出现，以考虑尾部 fin 对称性的进化和发育起源。
转基因报告基因和骨骼染色显示，下尾骨间区定义的间隙在第 2 和第 3 个下尾骨之间很早就形成，并将两块结缔组织的祖细胞分开。两组中央主射线（CPR）同步、顺序和对称地出现在间隙周围。最上面的两个背侧和腹侧射线（外周主射线，PPR）独立于相邻的 CPR 更早出现。肌肉和肌腱标记物显示不同的肌肉附着在 CPR 和 PPR 两组上。
我们提出，尾鳍对称性源自一个中央组织者，它建立了下尾骨间区，并将周围组织双向组织成两块结缔组织板和两组镜像的 CPR。此外，两个外围组织者单向指定 PPR，形成一个源自三个区域的对称“复合”尾鳍。不同的 CPR 和 PPR 个体发育可能代表赋予射线身份、肌肉连接和生物力学特性的发育模块。我们的模型将硬骨鱼 fin 形态变异的机制研究置于上下文中。
