Structure and tethering mechanism of dynein-2 intermediate chains in intraflagellar transport.

Dynein-2 is a large multiprotein complex that powers retrograde intraflagellar transport (IFT) of cargoes within cilia/flagella, but the molecular mechanism underlying this function is still emerging. Distinctively, dynein-2 contains two identical force-generating heavy chains that interact with two different intermediate chains (WDR34 and WDR60). Here, we dissect regulation of dynein-2 function by WDR34 and WDR60 using an integrative approach including cryo-electron microscopy and CRISPR/Cas9-enabled cell biology. A 3.9 Å resolution structure shows how WDR34 and WDR60 use surprisingly different interactions to engage equivalent sites of the two heavy chains. We show that cilia can assemble in the absence of either WDR34 or WDR60 individually, but not both subunits. Dynein-2-dependent distribution of cargoes depends more strongly on WDR60, because the unique N-terminal extension of WDR60 facilitates dynein-2 targeting to cilia. Strikingly, this N-terminal extension can be transplanted onto WDR34 and retain function, suggesting it acts as a flexible tether to the IFT "trains" that assemble at the ciliary base. We discuss how use of unstructured tethers represents an emerging theme in IFT train interactions.

Lis1-dynein drives corona compaction and limits erroneous microtubule attachment at kinetochores.

Mitotic cell division requires that kinetochores form microtubule attachments that can segregate chromosomes and control mitotic progression via the spindle assembly checkpoint. During prometaphase, kinetochores shed a domain called the fibrous corona as microtubule attachments form. This shedding is mediated, in part, by the minus-end directed motor dynein, which 'strips' cargoes along K-fibre microtubules. Despite its essentiality, little is known about how dynein stripping is regulated and how it responds to attachment maturation. Lis1 (also known as PAFAH1B1) is a conserved dynein regulator that is mutated in the neurodevelopmental disease lissencephaly. Here, we have combined loss-of-function studies, high-resolution imaging and separation-of-function mutants to define how Lis1 contributes to dynein-mediated corona stripping in HeLa cells. Cells depleted of Lis1 fail to disassemble the corona and show a delay in metaphase as a result of persistent checkpoint activation. Furthermore, we find that although kinetochore-tethered Lis1-dynein is required for error-free microtubule attachment, the contribution of Lis1 to corona disassembly can be mediated by a cytoplasmic pool. These findings support the idea that Lis1 drives dynein function at kinetochores to ensure corona disassembly and prevent chromosome mis-segregation.