[
International Worm Meeting,
2021]
During development, the centrosome acts as a microtubule organizing center (MTOC) in mitotic cells, forming radial arrays essential to separate cellular components between daughter cells. Microtubules are organized at the centrosome by pericentriolar material (PCM) complexes. After mitosis, during cell differentiation the fate of the centrosome is going to be diverse depending of cell fate. In differentiated epithelial cells, the centrosome is inactivated, losing its PCM and having the MTOC function redirected to other cellular components, in contrast, other ciliated cells have the centrosome and its centrioles repurposed into basal bodies to ciliary structures. We are using C. elegans as a model to characterize MTOC recruitment and regulation at the centrosome. In C. elegans, the PCM is organized around the centrioles in a partial concentric overlay of protein spheres, in which the two main scaffolding protein, SPD-2/CEP192 and SPD-5 which localize the microtubule nucleating complex -TuRC to the centrosome, partially overlap delimiting two main body - an inner sphere with both partner and an outer sphere with SPD-5 (Magescas et al 2019). Upon differentiation centrosome lose their PCM, leaving 'naked' centrioles, like in intestinal cells. Interestingly, analysis of SPD-5 and -TuRC proteins revealed that ciliated sensory neurons, SPD-5 and most MTOC proteins remains at the ciliary base while centriolar protein and SPD-2 are lost. Those complexes organize the MTOC function at the base of cilia and are critical for ciliogenesis, as depletion of SPD-5 produces aberrant cilia. Interestingly, contrary to the current model, similar loss of SPD-2 in cycling intestinal cells prior to differentiation doesn't result in the loss of SPD-5 at the centrosome, nor it impairs centrosomal function. Based on our data we propose that the PCM is composed of different subcomplexes revolving around SPD-5 that are differently regulated, working in parallel to drive the MTOC function.