Nutritional Regulation of Late Meiotic Events in Saccharomyces cerevisiae through a Pathway Distinct from Initiation†

Abstract

The IME1 gene is essential for initiation of meiosis in the yeast Saccharomyces cerevisiae, although it is not required for growth. Here we report that in stationary-phase cultures containing low concentration of glucose, cells overexpressing IME1 undergo the early meiotic events, including DNA replication, commitment to recombination, and synaptonemal complex formation and dissolution. In contrast, later meiotic events, such as chromosome segregation, commitment to meiosis, and spore formation, do not occur. Thus, nutrients can repress the late stages of meiosis independently of their block of initiation. Cells arrested at this midpoint in meiosis are relatively stable and can resume meiotic differentiation if transferred to sporulation conditions. Resumption of meiosis does not require repression of IME1 expression, since IME1 RNA levels stay high after transfer of the arrested cells to sporulation medium. These results suggest that meiosis in S. cerevisiae is a paradigm of a differentiation pathway regulated by signal transduction at both early and late stages.

Cell Differentiation and Spatial Organization in Yeast Colonies: Role of Cell-Wall Integrity Pathway

“…To confirm that Rlm1 stimulates spore formation in colonies largely by activating IME1 transcription, we overexpressed IME1 in a rlm1D colony using a high-copy-number plasmid (Lee and Honigberg 1996;Honigberg and Lee 1998) and measured both ime2-GFP expression and spore formation. Overexpression of IME1 increased ime2-GFP expression ( Figure 2C) and spore formation ( Figure 2D) in both RLM1 + and rlm1D colonies; thus, IME1 expression limits sporulation in both strains.…”

“…To ensure that only diploid cells could grow into colonies, the medium lacked both histidine and lysine (Lee and Honigberg 1996). To measure osmosensitivity of nonsporulated diploids, the preceding cell suspensions also were diluted 100-fold in distilled water and plated on His 2 Lys 2 medium lacking sorbitol.…”

The Ras/cAMP Pathway and the CDK-Like Kinase Ime2 Regulate the MAPK Smk1 and Spore Morphogenesis in Saccharomyces cerevisiae

“…Moreover, such refed cells can exit from the sporulation program and return to mitotic growth (RTG) as long as the commitment point (MI) has not been passed. The overproduction of IME1 in stationary-phase cells can induce meiotic recombination and SC formation, but glucose can stall further progression in late prophase, suggesting that nutritional signals can control later steps in the program through an IME1-independent pathway (Lee and Honigberg 1996). 1 The multiple nutrient-sensing pathways that control induction and progression of sporulation form an interconnected signaling network that includes the nitrogensensing (Tor2), glucose repression, glucose induction, alkaline-sensing (Rim101), and Ras/cAMP pathways (reviewed in Honigberg and Purnapatre 2003).…”

PP2ACdc55is required for multiple events during meiosis I

“…All strains are isogenic to SK1, 69,79 or W303, [71][72][73] backgrounds. Yeast gene nomenclature is found in Supplemental Table 2.…”

“…We determined trp1 recombination in the W303 strain described by Honigberg and colleagues. 70,71 arg4 and leu2 frequencies were determined in SK1 strains kindly provided by the laboratories of Alain Nicolas 72 and Rochelle Esposito, 73,74 respectively. Heteroalleles of trp1, leu2 or arg4 can be repaired through intragenic recombination, generating wild-type alleles.…”