Cilia and flagella of eukaryotes

As recognized by Irene Manton (1) at the time that the basic 9 + 2 structural uniformity of cilia and most eukaryotic flagella was first becoming recognized, these organelles are sufficiently complex that knowledge of their structure, no matter how detailed, cannot provide an understanding of their mechanisms of growth and function . In our understanding of these mechanisms, the substantial advances of the intervening 28 years have, for the most part, resulted from experiments in which it has been possible either to correlate changes in structure with the changes in waveform that occur during a normal beat cycle, or to make experimental changes in the structure, chemical properties, or mechanical loading of the organelle, and then relate these to the consequent changes in its motility . Research has thus tended to concentrate on organisms in which the cilia or flagella are suitable for study by as many techniques as possible . The number of organisms that readily yield sufficient cilia or flagella for protein chemistry is relatively small . Among these, the flagella of sea urchin spermatozoa have proved the most favorable for many purposes because their length of 4050 t.m is sufficient for detailed measurement of wave parameters, and they are rugged enough for the demembranated flagella to be reactivated easily with adenosine triphosphate (ATP) . The availability of mutants with altered flagella makes Chlamydomonas also a highly favorable material, although observation of the detailed pattern of motility is more difficult because the flagella are only 12-15 gm long . Cilia of Tetrahymena have been used as a source of ciliary proteins, and cilia of molluscan gills can also be obtained in good quantity, but, in both cases, observations of their motility are difficult to achieve, and have been useful mainly for investigating conditions that induce ciliary reversal or arrest. For experiments that do not involve protein chemistry, a broader choice oforganisms is available, including protozoa with a wide range of motility patterns and metazoa whose sperm flagellar structure differs substantially from the usual 9 + 2 organization .