Interaction of Circadian Oscillators and the Cell Developmental Cycle in Euglena

Abstract

Mechanisms proposed to control algal and microbial cell division cycles (CDC) often include the notion of timers and clocks (Edmunds, 1984a). Various types of autonomous biochemical and macromolecular oscillators have been proposed to underlie mitosis and other “landmarks” comprising the CDC (see Edmunds, 1984b, 1986; Edmunds & Laval-Martin, 1984). These range from those of the relaxation type, in which a single continuous variable accumulates or declines, triggering some event in the CDC when it reaches a critical threshold and then resetting to a baseline so that the cycle starts again, to those exhibiting limit cycle dynamics (Edmunds & Adams, 1981). In the latter, a central clock, characterized by a self-sustained oscillation of at least two continuously varying biochemical species, would maintain stable periodic behavior and coordinate the timing of events comprising the CDC despite transient perturbations in phase? it would continue to function even if mitosis and division were blocked. Circadian oscillators (CO’s) may underlie the persisting circadian rhythms (CR’s) of cell division or of “hatching”, having longer periods of 20–28 h, frequently observed in populations of algae, fungi and protozoa (Edmunds, 1984b; Edmunds & Adams, 1981; Edmunds & Laval-Martin, 1984). Our goal is to determine the biochemical nature of the oscillator(s) presumed to couple to and interact with the CDC and to generate these overt rhythmicities.