title: Sfr1, aTetrahymena thermophilaSfi1 Repeat Protein, Modulates the Production of Cortical Row Basal Bodies.
abstract: Basal bodies are essential microtubule-based structures that template, anchor, and orient cilia at the cell surface. Cilia act primarily in the generation of directional fluid flow and sensory reception, both of which are utilized for a broad spectrum of cellular processes. Although basal bodies contribute to vital cell functions, the molecular contributors of their assembly and maintenance are poorly understood. Previous studies of the ciliateTetrahymena thermophilarevealed important roles for two centrin family members in basal body assembly, separation of new basal bodies, and stability. Here, we characterize the basal body function of a centrin-binding protein, Sfr1, inTetrahymena. Sfr1 is part of a large family of 13 proteins inTetrahymenathat contain Sfi1 repeats (SFRs), a motif originally identified inSaccharomyces cerevisiaeSfi1 that binds centrin. Sfr1 is the only SFR protein inTetrahymenathat localizes to all cortical row and oral apparatus basal bodies. In addition, Sfr1 resides predominantly at the microtubule scaffold from the proximal cartwheel to the distal transition zone. Complete genomic knockout ofSFR1(sfr1Δ) causes a significant increase in both cortical row basal body density and the number of cortical rows, contributing to an overall overproduction of basal bodies. Reintroduction of Sfr1 intosfr1Δ mutant cells leads to a marked reduction of cortical row basal body density and the total number of cortical row basal bodies. Therefore, Sfr1 directly modulates cortical row basal body production. This study reveals an inhibitory role for Sfr1, and potentially centrins, inTetrahymenabasal body production.IMPORTANCEBasal bodies and centrioles are structurally similar and, when rendered dysfunctional as a result of improper assembly or maintenance, are associated with human diseases. Centrins are conserved and abundant components of both structures whose basal body and centriolar functions remain incompletely understood. Despite the extensive study of centrins inTetrahymena thermophila, little is known about how centrin-binding proteins contribute to centrin's roles in basal body assembly, stability, and orientation. The sole previous study of the large centrin-binding protein family inTetrahymenarevealed a role for Sfr13 in the stabilization and separation of basal bodies. In this study, we found that Sfr1 localizes to allTetrahymenabasal bodies and complete genetic deletion ofSFR1leads to overproduction of basal bodies. The uncovered inhibitory role of Sfr1 in basal body production suggests that centrin-binding proteins, as well as centrins, may influence basal body number both positively and negatively.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA.
authors.forename: Westley
authors.initials: W
authors.lastname: Heydeck
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Stemm-Wolf
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA.
authors.forename: Janin
authors.initials: J
authors.lastname: Knop
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA.
authors.forename: Christina C
authors.initials: CC
authors.lastname: Poh
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Winey
keywords: Sfi1 repeat; Tetrahymena; basal body; centrin; centriole; ciliates