Regulation of Nuclear Division and Ascosporogenesis in Apomictic Strains of Saccharomyces cerevisiae

Abstract

<p>Effects of nutritional alterations (carbon source, zinc) on nuclear division and protein synthesis during apomictic and meiotic differentiation in Saccharomyces cerevisiae strain 19el were investigated. The approach taken has led to identification of: physiological prerequisites for both developmental routes, landmark cytological and molecular events controlling the manner of nuclear division and spore production, other environmental modifications suppressing apomixis, and the period of sporulation during which a decision is made concerning the manner of differentiation.</p> <p>Unlike cells cultured under meiosis-promoting conditions, cells cultured under apomixis-promoting conditions exhibited extensive protein synthesis during the first 3 h of sporulation. Cycloheximide treatment of the latter cells induced meiosis and maximum yields of meiotic asci resulted when the treatment was given for the first 3 h in sporulation medium. Temperature shock treatments administered during early hours under sporulation-inducing conditions also increased the frequency of meiosis. Thus the data indicate that the decision concerning which developmental route, apomictic or meiotic, a given cell will follow is made shortly after transfer of cells to sporulation medium. Electrophoretic analysis of labeled proteins synthesized during sporulation revealed bands unique to both developmental routes.</p> <p>A novel microcytochemical staining procedure was developed to determine sites of zinc accumulation in vegetative and sporulating yeast. The procedure was used to monitor intracellular distribution of zinc during sporulation in an effort to integrate cytological with molecular data. The micronutrilite translocated from vacuolar to nuclear compartments during the early critical period of sporulation. Possible roles of zinc were considered and several hypotheses were offered to explain the restoration of meiosis in apomictic mutants by environmental manipulation.</p>