Circaseptan aspect of the chronome of a eukaryotic unicell

 

O. Schwartzkopff, G. Katinas, G. Cornelissen, F. Halberg

Halberg Chronobiology Center, University of Minnesota

 

Aims: With the late Hans-Georg Schweiger and the help of Sigrid Berger, who helped make this study possible, we sought, by an original study, a model for a built-in week (1). The Acetabularia model had been previously extensively used for the study of a biologic clock and aging (2-5). Thanks to data provided by Sigrid Berger, Jack Woolum and Luebbo von Lindern, collected for these other purposes, notably for assessing circadians, we found an experimental unicellular eukaryotic model of a much broader scope.

 

Background: It is to the credit of the late Hans-Georg Schweiger to have invested, at the end of his career, into the proposition that the week is built into us (1). There are many more rhythms than the circadians and circannuals, the visible associations of the sun, the photic cycles in the biosphere. There are also sometimes more or less hidden rhythms of non-photic origin that can be resolved as spectral components; these are usually of smaller amplitude and are wobblier in their period than the circadians or wobblier even than the often very wobbly biologic circannuals (6,7).

 

Methods: Oxygen evolution, the electrical potential and chloroplast migration were studied as described elsewhere under conditions of light and darkness alternating at 12-hour intervals and after the release of the alga into continuous light. The original determinations were detrended and residuals expressed as percentage of chronome- (time structure‑)adjusted average, i.e. MESOR, during LD or LL, in order to make values obtained from different cells comparable. Signal averaging, again on normalized data was done for each variable in LL. Linear-nonlinear rhythmometry followed (8).

 

Results: For oxygen production, under LD conditions 18 single cells all reveal statistically significant (P< 0.05) circadian (CD) oscillations, but only a third of them exhibit a circaseptan (CS) component. The CD amplitude was about 8 times larger than that of the CS. Hence the CD versus CS ratio was much smaller than unity in  LD; it became much larger than unity in LL, primarily because there was a decrease in circadian amplitude in LL. The difference of the amplitude ratios in LD versus LL was very highly statistically significant, since in LL conditions the amplitude ratio of CS/CD increased greatly, Fig. 1. The electrical potential and chloroplast migration also show that in LD the CD component dominates, whereas in LL the CS is more prominent. Signal averaging, with the data of each alga expressed as a percentage of mean, visualizes the larger than circadian amplitude of the circaseptan in the normalized values, Fig 2.

     In LL the CS component differs overall from a precisely weekly one for all three variables. Average periods are 160.7, 162.2 and 163.5 hours for oxygen production, chloroplast migration and electrical potential, respectively. Because these periods are close to each other, they were averaged and according to that averaged period of 162.13 hours three curves could be plotted. Acrophases of those periods differ with statistical significance, especially for oxygen production, that is approximately in anti-phase in relation to the other variables, Figure 3.

 

Discussion. For another variable of Acetabularia, enucleation is associated with an increase in this circaseptan/circadian amplitude ratio, a finding suggesting subtractive coupling between the nucleus and cytoplasm discussed elsewhere (9).

 

Conclusion: A division of labor in time is revealed by the differences among acrophases in 50 or more different variables in mammals such as mice and humans (10).  This finding is here extended to circaseptan acrophases in a eukaryotic unicell, which may have been on earth already perhaps about 500 million years ago.

 

1.         Schweiger H-G, Berger S, Kretschmer H, Mörler H, Halberg E, Sothern RB, Halberg F. Evidence for a circaseptan and a circasemiseptan growth response to light/dark cycle shifts in nucleated and enucleated Acetabularia cells, respectively. Proc Natl Acad Sci USA 1986; 83: 8619-8623.

2.         Berger S, Kaever MJ. Dasycladales: An Illustrated Monograph of a Fascinating Algal Order. Stuttgart: Thieme-Verlag, 1992.

3.         Schweiger H-G. Auf der Suche nach dem molekularen Mechanismus der circadianen Uhr. In: Boehringer Mannheim GmbH, hrsg. Mannheimer Forum 84/85. Mannheim: Boehringer Mannheim GmbH, 1984: 115-171.

4.         von Lindern L, Berger S, Mergenhagen D. High-resolution measurement of circadian periodicities in Acetabularia. Chronobiology International 1994; 11, 1-20.

5.         Mergenhagen D, Schweiger H-G. Recording the oxygen production of a single Acetabularia cell for a prolonged period. Exptl Cell Res 1973; 81: 360-364.

6.         Sothern RB, Katinas G, Cornélissen G, Halberg F. Moving spectra of circannual variation in normotensive diastolic blood pressure: Part I. This volume.

7.         Watanabe Y, Sothern RB, Katinas G, Cornelissen G, Otsuka K, Halberg F. Replication of anticipated circadecadal solar cycle modulation of cardiovascular circannual variation: Part III. This volume.

8.         Halberg F. Chronobiology: methodological problems. Acta med rom 1980; 18: 399-440.

9.         Halberg F. Chronobiology. Annu Rev Physiol 1969; 31: 675-725.

10.      Woolum JC, Cornélissen G, Halberg F. Chronometaanalysis: enucleation changes the infradian-circadian amplitude ratio of Acetabularia. Abstract, 6° Convegno Nazionale de Cronobiologia, Chianciano, Italy, November 27-28, 1998, p. 64.



Figure 1


Figure 2a

 



Figure 2b

 



Figure 3