The centrosome is an unusual organelle that lacks a surrounding membrane, raising the question of what limits its size and shape. Moreover, while electron microscopy (EM) has provided a detailed view of centriole architecture, there has been limited understanding of how the second major component of centrosomes, the pericentriolar material (PCM), is organized. Here, we summarize exciting recent findings from super-resolution fluorescence imaging, structural biology, and biochemical reconstitution that together reveal the presence of ordered layers and complex gel-like scaffolds in the PCM. Moreover, we discuss how this is leading to a better understanding of the process of microtubule nucleation, how alterations in PCM size are regulated in cycling and differentiated cells, and why mutations in PCM components lead to specific human pathologies.

The dynein-2 complex must be transported anterogradely within cilia to then drive retrograde trafficking of the intraflagellar transport (IFT) machinery containing IFT-A and IFT-B complexes. Here, we screened for potential interactions between the dynein-2 and IFT-B complexes and found multiple interactions among the dynein-2 and IFT-B subunits. In particular, WDR60/DYNC2I1 and the DYNC2H1–DYNC2LI1 dimer from dynein-2, and IFT54 and IFT57 from IFT-B contribute to the dynein-2–IFT-B interactions. WDR60 interacts with IFT54 via a conserved region N-terminal to its light chain-binding regions. Expression of the WDR60 constructs in WDR60-knockout (KO) cells revealed that N-terminal truncation mutants lacking the IFT54-binding site fail to rescue abnormal phenotypes of WDR60-KO cells, such as aberrant accumulation of the IFT machinery around the ciliary tip and on the distal side of the transition zone. However, a WDR60 construct specifically lacking just the IFT54-binding site substantially restored the ciliary defects. In line with the current docking model of dynein-2 with the anterograde IFT trains, these results indicate that extensive interactions involving multiple subunits from the dynein-2 and IFT-B complexes participate in their connection.

The primary cilium is a sensory organelle, receiving signals from the external environment and relaying them into the cell. Mutations in proteins required for transport in the primary cilium result in ciliopathies, a group of genetic disorders that commonly lead to the malformation of organs such as the kidney, liver and eyes and skeletal dysplasias. Motor proteins dynein-2 and kinesin-2 mediate retrograde and anterograde transport respectively in the cilium. WDR34, a dynein-2 intermediate chain, is required for the maintenance of cilia function. Here, we investigated WDR34 mutations identified in Jeune syndrome, short-rib polydactyly syndrome or asphyxiating thoracic dysplasia patients. There is a poor correlation between genotype and phenotype in these cases making diagnosis and treatment highly complex. We set out to define the biological impacts on cilia formation and function of WDR34 mutations by stably expressing the mutant proteins in WDR34 knockout cells. WDR34 mutations led to different spectrums of phenotypes. Quantitative proteomics demonstrated changes in dynein-2 assembly, whereas initiation and extension of the axoneme, localization of intraflagellar transport complex-B proteins, transition zone integrity, and Hedgehog signalling were also affected.

The primary cilium is a sensory organelle, receiving signals from the external environment and relaying them into the cell. Mutations in proteins required for transport in the primary cilium result in ciliopathies, a group of genetic disorders that commonly lead to the malformation of organs such as the kidney, liver and eyes and skeletal deformation. Motor proteins dynein-2 and kinesin-2 mediate retrograde and anterograde transport in the cilium. WDR34, a dynein-2 intermediate chain, is required for the maintenance of cilia function. Here, we investigated WDR34 mutations identified in Jeune syndrome, Short-rib polydactyly syndrome or Asphyxiating thoracic dysplasia patients by stably expressing the mutant proteins in WDR34 knockout cells. WDR34 mutations led to different spectrums of phenotypes. Each mutation results in a distinct profile of phenotypes. Quantitative proteomics demonstrated changes in dynein-2 assembly, whereas initiation and extension of the axoneme, IFT-B protein localization, transition zone integrity, and Hedgehog signaling were also affected.

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