Cell size control of development in Saccharomyces cerevisiae

Abstract

Diploid cells of the yeast Saccharomyces cerevisiae in the G₁ phase of the cell cycle are faced with the alternatives of either continuing vegetative cell division or undergoing the developmental processes of meiosis and subsequent ascospore formation, or adapting to starvation conditions if these apply. The course taken is influenced by the nutritional status of the culture medium¹, the presence of both MATa and MATα mating-type alleles², and the need for cells to be in the G₁ phase of the cell cycle³. For those cells that continue cell division, size controls operate in both the budding yeast S. cerevisiae^4,5 and the fission yeast Schizosaccharomyces pombe^6,7. In S. cerevisiae the ‘start’ event initiating the cell cycle is controlled in some way related to cell size because cells below a critical size fail to initiate cell division⁸. The ability of cells to undergo the developmental process of sporulation is related to cell age, in that cells gain this ability just before the emergence of the first bud⁹ and the process of sporulation after initiation is altered in small cells¹⁰. Here we report that the initiation of sporulation is subject to a size control related to absolute cell volume, which is distinct from control by cell age and also independent of the control operating on the initiation of cell division.