Microtubules inserted into the CP are bridged to the actin meshwork via filamentous linkers. A, 2D transmission electron microscopy of an inner ear hair cell from a 6-dpf zebrafish reveals a microtubule (arrowhead) terminating within the CP. Asterisk shows position of the apical surface of the cell. B, A ∼1-nm-thick slice through a tomographic 3D reconstruction corresponding to the 2D projection view shown in A. C, An enlarged view of rectangle in B. Arrowhead indicates a filamentous connection, which bridges the gap between the microtubule and actin. D, E, Manual segmentation and surface rendering of the densities of interest, with microtubule depicted in mint, actin meshwork in purple, and connecting filaments in red, revealing a ∼15- to 20-nm-wide gap between the microtubule and the actin meshwork, which is bridged by the filamentous connections. Boundary of the actin meshwork is indicated in blue. Mitochondria adjacent to the CP are shown in yellow and green. D, Surface rendering of the segmented volume overlaid onto a central section through the 3D reconstruction. E contains only the segmented volume from D. Scale bars, 200 nm. F, Models of ACF7 function in the mature hair cell. Top, Image of a hair cell. CP and circumferential band (CB) are represented as solid purple structures. Blue structure is the basal body, which resides in the fonticulus. ACF7 is shown in red. Model 1, ACF7 links a microtubule (mint), which penetrates into the CP, with the F-actin of the CP. Model 2, ACF7 links F-actin of the circumferential band to a microtubule. Model 3, A microtubule that emanates from the basal body is joined to F-actin of the CP by ACF7.