Evidence for regional differences in the dynamics of centrin cytoskeletal structures in the polymorphic hymenostome ciliate Tetrahymena paravorax

Centrins are ubiquitous EF-hand calcium-binding proteins which, in higher e ukaryotes, are almost exclusively confined to centrioles and/or kinetosomes . The experimental results obtained from work with protists are entirely co nsistent with this view, but also indicate that centrins can form calcium-s ensitive filamentous networks which represent significant components of the cytoskeleton in many ciliates and flagellates. In this study, the distribu tion of centrin has been investigated by immunofluorescence in the polymorp hic ciliate Tetrahymena paravorax, with special attention to centrin-based cytoskeletal systems and their changes during cell division, microstome - m acrostome transformation and standard oral replacement (microstome - micros tome). In non-dividing microstomal cell types, centrin was demonstrated in the "apical filamentous ring" (AFR), a structure situated directly undernea th the apical crown of kinetosome couplets, and in a crescent-shaped struct ure located in the right-posterior part of the oral apparatus. Cell divisio n and macrostome formation correlate with a transient disassembly-reassembl y cycle and dramatic reorganization of the oral crescent respectively, whil e the assembly state of the AFR remains unaffected throughout the whole cel l cycle in T. paravorax. This study therefore emphasizes the existence of r egional differences in the dynamics of the centrin-based cytoskeleton and s uggests a specific control of these systems in relation with cortical morph ogenesis.