Highlights d SPD-5 is physically and functionally central to the MTOC function of the centrosome d SPD-5 and PCMD-1 are maintained at the ciliary base in the absence of a centriole d Centriole-less pericentriolar material at the base of C. elegans cilia is an MTOC d A module of SPD-5 and g-TuRC drives MTOC function at the ciliary base

During mitosis in animal cells, the centrosome acts as a microtubule organizing center (MTOC) to assemble the mitotic spindle. MTOC function at the centrosome is driven by proteins within the pericentriolar material (PCM), however the molecular complexity of the PCM makes it difficult to differentiate the proteins required for MTOC activity from other centrosomal functions. We used the natural spatial separation of PCM proteins during mitotic exit to identify a minimal module of proteins required for centrosomal MTOC function in C. elegans. Using tissue specific degradation, we show that SPD-5, the functional homolog of CDK5RAP2, is essential for embryonic mitosis while SPD-2/CEP192 and PCMD-1, which are essential in the zygote, are dispensable. Surprisingly, although the centriole is known to be degraded in the ciliated sensory neurons in C. elegans [1-3], we find evidence for 'centriole-less PCM' at the base of cilia and use this structure as a minimal testbed to dissect centrosomal MTOC function. Super-resolution imaging revealed that this PCM inserts inside the lumen of the ciliary axoneme and directly nucleates the assembly of dendritic microtubules towards the cell body. Tissue-specific degradation in ciliated sensory neurons revealed a role for SPD-5 and the conserved microtubule nucleator γ-TuRC, but not SPD-2 or PCMD-1, in MTOC function at centriole-less PCM. This MTOC function was in the absence of regulation by mitotic kinases, highlighting the intrinsic ability of these proteins to drive microtubule growth and organization and further supporting a model that SPD-5 is the primary driver of MTOC function at the PCM.

Microtubule doublets (MTDs) are a well conserved compound microtubule structure found primarily in cilia. However, the mechanisms by which MTDs form and are maintained in vivo remain poorly understood. Here, we characterize microtubule-associated protein 9 (MAP9) as a novel MTD-associated protein. We demonstrate that C. elegans MAPH-9, a MAP9 homolog, is present during MTD assembly and localizes exclusively to MTDs, a preference that is in part mediated by tubulin polyglutamylation. Loss of MAPH-9 caused ultrastructural MTD defects, dysregulated axonemal motor velocity, and perturbed cilia function. As we found that the mammalian ortholog MAP9 localized to axonemes in cultured mammalian cells and mouse tissues, we propose that MAP9/MAPH-9 plays a conserved role in supporting the structure of axonemal MTDs and regulating ciliary motors.

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The 2021 Annual Joint Meeting (AJM) and Young Investigators’ Forum of the Canadian Society for Clinical Investigation / Société Canadienne de Recherches Clinique (CSCI/SCRC) and Clinician Investigator Trainee Association of Canada/Association des Cliniciens-Chercheurs en Formation du Canada (CITAC/ACCFC) was hosted virtually on November 14–16th, 2021. The theme of the AJM was “Communication, Collaboration, and Tools for the Next Generation of Clinician Scientists”, and emphasized lectures, panels and interactive workshops designed to provide knowledge and skills for professional development of clinician investigator trainees. The opening remarks were given by Nicola Jones (President of CSCI/SCRC) and Adam Pietrobon (Past President of CITAC/ACCFC). The keynote speaker was Dr. Timothy Caulfield, who delivered the presentation titled “Communication in the Era of Misinformation”. Dr. Michael Hill (University of Calgary) received the CSCI Distinguished Scientist Award and Dr. Philippe Campeau (Université de Montréal) received the CSCI Joe Doupe Young Investigator Award. Each of the scientists delivered award winning talks during the symposium titled “All the King’s Horses and All the King’s Men” and “Understanding Growth Plate Disorders to Better Treat Them”, respectively. The three interactive workshops included “Data Visualization”, “Science Communication on Social Media” and “Mentorship in Action”. The two panels were “CIHR Engagement: Challenges and Opportunities in the Clinician Investigator Career Path” and “Early Career Investigator Panel”. The AJM also included presentations from clinician investigator trainees from across the country. Over 60 abstracts were showcased at this year’s meeting, most of which are summarized in this review. Six outstanding abstracts were selected for oral presentations during the President’s Forum.