Sfr13 is a member of a large family of asymmetrically 1 localized Sfi1-repeat proteins and is important for basal body separation and stability in Tetrahymena thermophila

Abstract

Directed fluid flow, which is achieved by the coordinated beating of motile cilia, is required for processes as diverse as cellular swimming, developmental patterning, and mucus clearance. Cilia are nucleated, anchored and aligned at the plasma membrane by basal bodies, cylindrical microtubule based structures with nine-fold radial symmetry. In the unicellular ciliate, Tetrahymena thermophila, two centrin family members associated with the basal body are important for both basal body organization and stabilization. We have identified a family of thirteen proteins in Tetrahymena containing centrin-binding repeats, related to those identified in the Saccharomyces cerevisiae Sfi1 protein, that we have named Sfr1-13 for Sfi1-repeat. Nine of the Sfr proteins localize in unique polarized patterns surrounding the basal body, suggesting non-identical roles in basal body organization and association with basal body accessory structures. Furthermore, the Sfr proteins are found in distinct basal body populations in Tetrahymena cells, indicating they are responsive to particular developmental programs. A complete genetic deletion of one of the family members, Sfr13, causes unstable basal bodies and defects in daughter basal body separation from the mother, phenotypes also observed with centrin disruption. It is likely the other Sfr family members are involved in distinct centrin functions, providing specificity to the tasks centrins perform at basal bodies.