Studies on the Molecular Mechanisms That Produces and Controls Flagellar and Ciliary Movements

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This research has been aimed at the elucidation of the molecular mechanism that generates and controls flagellar and ciliary movements. The beating of flagella and cilia is based on the sliding movement between adjacent microtubules, driven by dynein arms. Through examination of the structure of dynein arms and properties of the sliding movement, we obtained the following important findings : 1) Outer dynein arms in multicellular organisms always contain two heavy chains, whereas those in unicellular organisms have three heavy chains ; 2) The three intermediate chains in the outer arm dynein have enzyme activities involved in nucleotide metabolism ; 3) Inner arm dynein contains true actin as a subunit ; 4) The activity of dynein function may be regulated through nucleotide binding to multiple sites in the dynein heavy chain ; 5) Dynein itself may have a nature to produce oscillatory movements. 6) Outer arm dynein and inner arm dynein appears to have different properties of force production. Regarding the regulation of ciliary and flagellar movements, we examined the effect of protein phosphorylation and calcium ion. We first obtained evidence that the site of phosphorylation-based regulation in mammalian sperm fagella is located at their bases ; protein phosphorylation at the base appears to regulate whether the flagella initiate beating. In Paramecium cilia, Phosphorylation appears to modulate the sensitivity to calcium. Thus, ciliary movements appear to be regulated by the coordination of calcium ion and protein phosphorylation. In beating sea urchin sperm axonemes, microtuble sliding is apparently regulated by calcium ion. However, the velocity of microtubule sliding under load-free conditions is not affected by calcium. Thus, calcium ion appears to regulate the force generation, possibly by regulating the number of active dynein arms. How calcium regulates the activity of dynein remains an important future problem.