Urodelan amphibian larvae develop three pairs of branching external gills on both sides of the pharyngeal region, and this study focuses on motile cilia on the gill surface. High-speed camera was used to observe ciliary strokes on the surface of the external gills of Pleurodeles waltl larvae. We found that the directionality of ciliary beating is position-dependent on the gill surface, and this rule is applicable to all the samples examined. For visualizing water flow around the external gills, we used bead suspensions. We revealed continuous anterior-to-posterior water flow generated by coordinated ciliary beating. Around the frontal surface of the gill stem (gill rachis), water flows countercurrent to the bloodstream beneath the gill epidermis. These results suggest that ciliary beating in each ciliated cell is coordinated, which cooperatively generates continuous and directional ciliary flow. We next visualized the overall distribution of ciliated cells on the gill surface by immunostaining of acetylated alpha-tubulin. Our results showed that the fine branches of external gills (fimbriae) have a circumferential distribution of cilia aligned orthogonal to the longitudinal axes of fimbriae, which facilitates water flow from proximal to the distal part of the fimbriae through the gills. This ciliary distribution pattern and directionality of cilia-driven flow are shared among five urodelan and two anuran species. Taken together, our findings suggest that the distribution and motility of ciliated cells on the surface of external gills is finely controlled, and this might support efficient respiration by the gills in urodeles.

中文翻译：

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微调的纤毛排列和协调的跳动在 Pleurodeles waltl 幼虫的外鳃上产生连续的水流

Urodelan 两栖动物幼虫在咽部两侧发育三对分枝的外鳃，本研究重点研究鳃表面的活动纤毛。使用高速摄像机观察Pleurodeles waltl 幼虫外鳃表面的睫状体。我们发现睫状跳动的方向性取决于鳃表面的位置，并且该规则适用于所有检查的样品。为了可视化外鳃周围的水流，我们使用了珠子悬浮液。我们揭示了由协调的纤毛搏动产生的连续的前后水流。在鳃茎（鳃轴）的前表面周围，水与鳃表皮下的血流逆流流动。这些结果表明，每个纤毛细胞中的纤毛跳动是协调的，其协同产生连续和定向的纤毛流动。我们接下来通过乙酰化α-微管蛋白的免疫染色观察了鳃表面纤毛细胞的整体分布。我们的结果表明，外鳃（菌毛）的细枝具有与菌毛纵轴正交排列的周向分布的纤毛，这有利于水从菌毛的近端到远端流过鳃。纤毛驱动流的这种纤毛分布模式和方向性在五种 urodelan 和两种 anuran 物种之间共享。综上所述，我们的研究结果表明，外鳃表面纤毛细胞的分布和运动受到很好的控制，这可能支持 urodeles 中鳃的有效呼吸。