Eukaryotic flagella/cilia are bending apparatus with >300 proteins. Sliding between microtubule doublets by dynein motors, which forms inner (waveform determination) and outer (accelerator) arms, is motility force. However, integration of linear dynein motility into well-organized bending is unclear. To address this question, localization and interaction of dynein and regulatory proteins are essential. We reconstructed structure of flagella/cilia at pseudo-atomic resolution utilizing electron cryo-tomography. We located the positions of eight major inner dyneins from 11 known in Chlamydomonas genome as well as other dyneins which exist locally in flagella (minor dyneins): at the proximal 2 micron area or on one microtubule doublet. This could explain asymmetric waveform with a sharp kink. We also reconstructed the radial spoke (RS), which are supposed to regulate by calcium (Pigino et al. (2011) JCB, in press). Chlamydomonas has two RSs, while Tetrahymena has three. Interestingly Chlamydomonas also has a short protrusion at the position of Tetrahymena RS3, which resembles RS3, suggesting evolutional pathway. Mutant structures revealed connection of 23 component proteins (figure). Calmodulins are localized at the branch of bifurcation and the bottom, close to the interface between RS and dynein tail.View Large Image | View Hi-Res Image | Download PowerPoint Slide