High-resolution structure of mouse radial spoke and its in-situ structure in ependymal cilia revealed by cryo-EM and cryo-ET

Abstract

Radial spokes (RS) transmit mechanochemical signals between the central pair (CP) and axonemal dynein arms to coordinate ciliary motility. However, the high-resolution structure of mammalian RS remains missing. Here, we present the high-resolution cryo-EM structure of mouse RS head-neck complex in both monomer and dimer forms and reveal the intrinsic dynamics of the dimer. We also map the genetic mutations related to primary ciliary dyskinesia and asthenospermia on the head-neck complex. Moreover, we present the unprecedented cryo-ET and sub-tomogram averaging map of mouse ependymal cilia, whose beating creates unidirectional cerebrospinal fluid flow, and build the models for RS1-3, IDAs, and N-DRC. Strikingly, our cryo-ET map reveals the lack of IDA-b/c/e and the absence of tektin filaments within the A-tubule of doublet microtubules in ependymal cilia compared with mammalian respiratory cilia and sperm flagella. This tissue-specific feature may represent an evolutionary choice driven by the functional requirements on ependymal cilia. Our findings reveal the RS head-neck assembly mechanism, shed light on the coordinated rigid and elastic RS-CP interaction modes beneficial for the regulation of asymmetric ciliary beating, and also facilitate understandings on the etiology of ciliary dyskinesia-related ciliopathies.

Distinct Roles of Kif6 and Kif9 in Mammalian Ciliary Trafficking and Motility

“…Nevertheless, the image resolutions were still insufficient for a definite conclusion whether the entire axonemal ultrastructure was the same as the wild-type one (Fig. 7b) (Meng et al, 2023). Interestingly, we observed that, while BFs were oriented towards a similar direction in the wild-type ependymal cells, a state termed the rotational polarity of BBs (Ohata and Alvarez-Buylla, 2016), BFs in Kif6 -/ependymal cells were misoriented regardless of the severity of hydrocephalus (Fig.…”