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PEARSON LAB DESCRIPTION

Centriole Biogenesis and Stabilization for Centrosomes and Cilia

In the Pearson Lab, we delve into several fascinating aspects of centrioles and basal bodies as they perform roles in organizing centrosomes and cilia. Centrosomes consist of a pair of centrioles surrounded by a matrix of pericentriolar material that nucleates cytoplasmic microtubules. During G0/G1 of the cell cycle, centrioles are commonly modified to serve as basal bodies that organize cilia. These cilia (known as primary cilia), sense their environment and transmit signals to the cell nucleus. Other cells produce motile cilia that produce hydrodynamic force generating fluid flow. In the case of motile cilia and the basal bodies that organize them, we capitalize on the ciliated protist, Tetrahymena thermophila, to understand how centrioles and basal bodies assemble, organize at the cell surface and resist mechanical stress produced by ciliary beating.

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MOULIS TALK

Basal body associated striated fibers control their length to organize ciliary arrays

Adam Soh, John V. Dam, Alex Stemm-Wolf, Chad G. Pearson

Multi-ciliary arrays are fields of motile cilia that beat in a coordinated and polarized manner. This organization of cilia is promoted by the basal bodies (BB) that nucleate, anchor and position cilia at the cell cortex. Extending from the base of every BB, striated fibers (SFs) connect BBs to each other and to the cell’s cortex. SF are structurally conserved polymers composed of striations with varying periodicities depending on the organism. Tetrahymena SFs possess striations of 27 nm. Tetrahymena cells possess a network of polarized BBs and SFs that link the approximately 500 BBs per cell. The loss of SFs causes BB and ciliary disorganization that is exacerbated by increased ciliary beating forces. Consistent with a role for SFs in resisting ciliary forces, Tetrahymena SFs lengthen when ciliary beating is elevated. Conversely, SFs shorten when ciliary forces are reduced. This suggests that SFs modulate their length in response to their hydrodynamic environment.  We next studied the structure and protein dynamics of SFs to understand how SF length is controlled. The periodicity between SF striations does not change even when changes to the total SF length occurs. The SF architecture comprises a complex network of 10 SF-assemblin-like proteins. Tetrahymena cells possess the SF-assemblin homologue that forms the core SF structure in algae. In addition, other SF-assemblin-like proteins localize to unique domains within the SF structure. As SFs lengthen during maturation or force induced elongation, the level of SF protein components increases. Thus, local SF protein component levels likely promote SF elongation. In summary, we provide a mechanistic basis for how the complex molecular architecture of SFs controls their length in response to ciliary forces.