Intracellular handedness in ciliates.
Ciliated protozoa have intrinsically asymmetrical ciliary structures that are asymmetrically arranged over the cell surface. These structures can be arranged in two enantiomorphic configurations, 'right-handed' (RH) and 'left-handed' (LH). Whereas one of these configurations (arbitrarily, RH) is apparently universal in Nature and predominant in the laboratory, mirror-image (RH-LH) doublets and reverse (LH) singlets have been generated and studied in eight different ciliate genera. In all these, the internal asymmetry of individual ciliary structures remains normal even when the asymmetry of arrangement of these structures is reversed. The individual structures may sometimes become inverted (rotationally permuted). LH forms reproduce themselves if they are able to feed, or reorganize periodically before starving to death if they are not. Changes of cellular handedness depend upon unusual geometric configurations and in most cases are unrelated to genic changes. In hypotrich ciliates changes of handedness can be provoked by artificially generated juxtapositions of anterior and posterior cell regions or of right and left cell margins. Reversal of handedness in ciliates can be visualized as a consequence of (re-)establishment of a normal sequence of normally spaced positional values following geometric disturbances created by the experimenter or by the regulating cell.
Frankel
J
J
Department of Biology, University of Iowa, Iowa City 52242.
D000818:Animals; D002454:Cell Differentiation; D002455:Cell Division; D002923:Cilia / Q000502:physiology / Q000648:ultrastructure*; D016798:Ciliophora / Q000502:physiology / Q000648:ultrastructure*; D007536:Isomerism; D008954:Models, Biological