The cell cycle in the fission yeast, Schizosaccharomyces pombe. VI. Relationship between cell size and division delay due to nutritional shift-up.

Abstract

The shift of a synchronous culture of the fission yeast, Schizosaccharomyces pombe, from a poor to a rich medium resulted in division delay.The mean time period from the shift till division was nearly constant, regardless of the time of shift in the cell cycle.The time period from the shift till division of the individual cells was negatively proportional to cell size at the shift. The division size of the shifted cells was larger than that of exponentially proliferating cells.From these results, the dependence of the timing of division on cell size at the shift, not at division, is discussed.In exponentially proliferating cells of lower eukaryotes, the attainment of a critical size required to initiate nuclear and cell division has been much discussed (1). In the fission yeast, Schizosaccharomyces pombe, NURSE (2) and FANTES and NURSE (3) proposed that size control was involved in entry into nuclear division.The cell size at division (the division size) and the cycle duration of normally elongated cells of S. pombe can be homeostatically controlled (4, 5). When oversized cells of S. pombe, produced by pulse treatment with hydroxyurea, were transferred from a rich medium (YM-medium) to a poor one (M-medium), they synchronously divided twice but not elongate (6). In both normally and nonelongating cells, the cycle durations were negatively proportional to the cell size at birth (the birth size), except that the cycle duration of cells larger than a particular size was consistently minimum. Thus, we proposed that the cycle duration depended on the birth size, not on the division size (6).FANTES and NURSE (3) found the division delay in cells of S. pombe due to the nutritional shift-up. The pattern of cell proliferation in asynchronous cultures perturbed by the shift (3) was similar to that with perturbation by heat shock (7).