Figure 2.

Cryo-ET reveals actin-like filaments within the microtubule lumen. (A) An XY plane (left), a series of transverse sections (middle), and a Z-series (right) though a 3D reconstruction of 23-microtubule (MT) projection. Sections that bisect the microtubule lumen reveal a mixture of particles and filamentous material with apparent helical properties. Light blue arrows highlight several lumenal filaments. The orange box region highlights filaments of the Class I form and the blue box the Class II, as described in more detail in Fig. 4. (B) A 3D model where microtubules are represented as colored 24 nm diameter cylinder segments (corresponds to Video 2). Microtubules are organized in a closely packed twisted membrane-bound bundle with some vesicular structures in swellings at the periphery. Scale bars are 100 nm.