The axoneme: the propulsive engine of spermatozoa and cilia and associated ciliopathies leading to infertility.

This review article provides a critical analysis of the structure and molecular mechanisms of the microtubule axoneme of cilia and sperm flagella and their associated elements required for male fertility.A broad range of genetic and molecular defects (ciliopathies) are considered in the context of human diseases involving impaired motility in cilia and sperm flagella, providing provocative thought for future research in the area of male infertility.

Cryo-electron tomography reveals conserved features of doublet microtubules in flagella.

The axoneme forms the essential and conserved core of cilia and flagella. We have used cryo-electron tomography of Chlamydomonas and sea urchin flagella to answer long-standing questions and to provide information about the structure of axonemal doublet microtubules (DMTs). Solving an ongoing controversy, we show that B-tubules of DMTs contain exactly 10 protofilaments (PFs) and that the inner junction (IJ) and outer junction between the A- and B-tubules are fundamentally different.

Functional protofilament numbering of ciliary, flagellar, and centriolar microtubules.

This article discusses the current state of knowledge about the evolutionarily conserved structure of ciliary, flagellar and centriolar microtubules, and formally proposes a functional numbering convention for their protofilaments.

Tektin interactions and a model for molecular functions.

Tektins from echinoderm flagella were analyzed for microheterogeneity, self-associations and association with tubulin, resulting in a general model of tektin filament structure and function applicable to most eukaryotic cilia and flagella. Using a new antibody to tektin consensus peptide RPNVELCRD, well-characterized chain-specific antibodies and quantitative gel densitometry, tektins A, B and C were found to be present in equimolar amounts in Sarkosyl-urea-stable filaments. In addition, two isoforms of tektin A are present in half-molar ratios to tektins B and C.

Rib72, a conserved protein associated with the ribbon compartment of flagellar A-microtubules and potentially involved in the linkage between outer doublet microtubules.

Ciliary and flagellar axonemes are basically composed of nine outer doublet microtubules and several functional components, e.g. dynein arms, radial spokes, and interdoublet links.