Resistive force theory and wave dynamics in swimming flagellar apparatus isolated from C. reinhardtii

In basal apparatus isolated from C. reinhardtii, if the frequency mismatch is high, mechanical or hydrodynamic coupling cannot synchronize them.

Centrin Scaffold in Chlamydomonas reinhardtii Revealed by Immunoelectron Microscopy

ABSTRACT In the flagellate green alga Chlamydomonas reinhardtii the Ca2+-binding EF-hand protein centrin is encoded by a single-copy gene. Previous studies have localized the protein to four distinct structures in the flagellar apparatus: the nucleus-basal body connector, the distal connecting fiber, the flagellar transitional region, and the axoneme. To explain the disjunctive distribution of centrin, the interaction of centrin with as yet unknown specific centrin-binding proteins has been implied. Here, we demonstrate using serial section postembedding immunoelectron microscopy of isolated cytoskeletons that centrin is located in additional structures (transitional fibers and basal body lumen) and that the centrin-containing structures of the basal apparatus are likely part of a continuous filamentous scaffold that extends from the nucleus to the flagellar bases. In addition, we show that centrin is located in the distal lumen of the basal body in a rotationally asymmetric structure, the V-shaped filament system. This novel centrin-containing structure has also been detected near the distal end of the probasal bodies. Taken together, these results suggest a role for a rotationally asymmetric centrin “seed” in the growth and development of the centrin scaffold following replication of the basal apparatus.

A Novel 95-kD Protein Is Located in a Linker between Cytoplasmic Microtubules and Basal Bodies in a Green Flagellate and Forms Striated Filaments In Vitro

The flagellar basal apparatus comprises the basal bodies and the attached fibrous structures, which together form the organizing center for the cytoskeleton in many flagellated cells. Basal apparatus were isolated from the naked green flagellate Spermatozopsis similis and shown to be composed of several dozens of different polypeptides including a protein band of 95 kD. Screening of a cDNA library of S. similis with a polyclonal antibody raised against the 95-kD band resulted in a full-length clone coding for a novel protein of 834 amino acids (90.3 kD). Sequence analysis identified nonhelical NH2- and COOH-terminal domains flanking a central domain of ∼650 residues, which was predicted to form a series of coiled-coils interrupted by short spacer segments. Immunogold labeling using a polyclonal antibody raised against the bacterially expressed 95-kD protein exclusively decorated the striated, wedge-shaped fibers, termed sinister fibers (sf-fibers), attached to the basal bodies of S. similis. Striated fibers with a periodicity of 98 nm were assembled in vitro from the purified protein expressed from the cloned cDNA indicating that the 95-kD protein could be a major component of the sf-fibers. This structure interconnects specific triplets of the basal bodies with the microtubular bundles that emerge from the basal apparatus. The sf-fibers and similar structures, e.g., basal feet or satellites, described in various eukaryotes including vertebrates, may be representative for cytoskeletal elements involved in positioning of basal bodies/centrioles with respect to cytoskeletal microtubules and vice versa.