Abstract

Meiotic differentiation was investigated using a synchronous meiotic system of the yeast, Saccharomyces cerevisiae, with respect to revertibility to mitotic division. When cells were transferred from a sporulation (SPM) to a growth (YHA) medium, reversion to mitosis took place at all stages up to and including the post synthetic phase of DNA. Continuous treatment with 4 mM hydroxyurea (HU) during sporulation resulted in the extension of the the premeiotic S phase. Revertibility to mitosis also was extended after the lengthened S phase. Pulse treatment with 50 min HU for 2 h during the premeiotic S phase caused a 2-h delay in the revertibility to mitosis. Similar results were obtained by treatment with elevated temperatures. The results demonstrate an irreversible commitment of cells to meiosis after the completion of premeiotic DNA replication.

When cells were transferred from SPM to poor nutrient media, the timing of their reversion to mitosis varied. If transferred to glucose-based media, cells in the premeiotic S phase underwent mitosis; whereas, if transferred to acetate-based media, they continued meiotic development. Thus, conversion to meiosis depends on the nutritional environment to which cells are transferred, which implies that a sequence of intracellular change during premeiosis leads to meiotic differentiation.

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