The two human centrin homologues have similar but distinct functions atTetrahymenabasal bodies

Abstract

Centrins are a family of small calcium-binding proteins found at basal bodies. The family can be separated into two groups based on sequence homology to the human centrins. The model organism Tetrahymena was used to show that the two centrin groups have similar but distinct functions at basal bodies.

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

“…In addition to its role in the developing oral apparatus, Sfr13 promotes the separation and/or reorientation of new cortical row basal bodies after assembly has been initiated. This phenotype is similar to that reported for the knockdown of PtCEN3 (Ruiz et al, 2005), and for its homologue, Tetrahymena CEN2 (Vonderfecht et al, 2012), suggesting that Sfr13 and Cen2 may directly interact with each other. One intriguing possibility is that Sfr13 plays a role in the assembly or function of the newly identified anterior left filament (ALF), which is present at assembling basal bodies, requires PtCEN3 function in Paramecium, and may play a role in daughter basal body positioning (Jerka-Dziadosz et al, 2012).…”

“…How the proper basal body arrangement is established is not yet well understood, but it seems likely that different organizational patterns will require different sets of proteins. Centrins, known to have roles in establishing the proper site of basal body assembly and in reorienting and separating basal bodies after assembly (Ruiz et al, 2005;Vonderfecht et al, 2011;Vonderfecht et al, 2012), interact with a number of proteins with the Sfi1 centrin binding domain (Azimzadeh et al, 2009;Gogendeau et al, 2007;Gogendeau et al, 2008;Kilmartin, 2003). It is interesting that many of these Sfr proteins in Tetrahymena are limited to specific classes of basal bodies, which leads to the possibility that they are required for specific basal body developmental programs.…”

“…Two centrins, Cen1 (human Cetn2 homologue) and Cen2 (human Cetn3 homologue), reside primarily at basal bodies, and both proteins have populations that localize asymmetrically to the anterior side of the basal body where new basal body assembly is initiated (StemmWolf et al, 2005). Both centrin proteins are required for basal body stability and, like Paramecium basal body centrins, for the proper orientation of new basal body assembly (Ruiz et al, 2005;StemmWolf et al, 2005;Vonderfecht et al, 2011;Vonderfecht et al, 2012). To investigate the mechanisms by which centrin affects stability, orientation and asymmetry of basal bodies, an examination of Tetrahymena Sfi1-repeat proteins was undertaken.…”

“…S4A; Table S1). Centrins in Tetrahymena are required for basal body stability (Stemm-Wolf et al, 2005;Vonderfecht et al, 2011;Vonderfecht et al, 2012). To test whether Sfr13 is involved in basal body stability, cells were shifted into starvation media where basal body assembly is eventually suspended but existing basal bodies persist (Pearson et al, 2009a).…”

“…Because centrin is also important for the proper orientation of basal bodies (Ruiz et al, 2005;Vonderfecht et al, 2011;Vonderfecht et al, 2012), basal body orientation was examined in the sfr13D strain through an analysis of the angle of the Antibodies against GFP were used to localize N-terminally tagged GFP-Sfr13. Gold particles conjugated to the secondary antibody are indicated by the red arrows.…”