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Fig. 1 Apical cilia are present in Kupffer's vesicle, the central canal of the spinal cord and pronephric ducts. Immunostaining of acetylated tubulin. (A) Apical cilia are present in cells lining Kupffer's vesicle at the 8-somite stage (arrowhead) in midline longitudinal sections. (D) Kupffer's vesicle; higher magnification (DAPI nuclear staining in blue). (B) Ependymal cells along the central canal bear cilia at 24 hpf (arrowheads). (E) Cross section at 44 hpf; cilia arise from all cells of the spinal central canal. (C) Cilia can also be seen in the pronephric duct at 48 hpf (arrowheads). (F) Cells double stained for acetylated tubulin and the alpha1 subunit of the NaK-ATPase confirmed the apical position of the pronephric cilia. (G-I) EM cross sections of cilia in Kupffer's vesicle (G) show a 9+2 structure; ependymal cell cilia (H) are 9+0 in structure; pronephric cilia (I) are 9+2 with clear dynein outer arms (arrows). Cilia beat pattern: (J) The cilia in the of the spinal central canal and Kupffer's vesicle rotate in an counterclockwise orientation. (K) In the pronephric duct monociliated and multiciliated cells can be observed. Their cilia beat in rotation like a corkscrew with an undulating appearance along their longitudinal axis. Mean values for cilia length and beat frequency are given for comparison. Scale bars: 100 µm in A-C; 10 µm in D-F; 250 nm in G-I. KV, Kupffer's vesicle; PND, pronephric duct; SCC, spinal central canal.