mRNA Decay Is Rapidly Induced after Spore Germination ofSaccharomyces cerevisiae

Abstract

Spores from the yeast Saccharomyces cerevisiae can germinate and resume their vegetative growth when placed in favorable conditions. Biochemical studies on germination have been limited by the difficulty of obtaining a pure population of spores germinating synchronously. Here, we report that spores can be purified and sorted according to their size by centrifugal elutriation and that these spores are able to germinate synchronously. Synchronizing their development has allowed reevaluating certain parameters of germination, and we demonstrate that both transcription and translation are induced very rapidly after germination induction. Spores contain mRNAs that are stable for several months in spores kept at 4°C. Germination induction leads to very rapid degradation of these mRNAs, thus providing a simple model to study induction of mRNA decay in eukaryotes. mRNAs from the spore are polyadenylated, capped, and cosediment on sucrose gradients with ribosomes and polysomes and with components of the mRNA degradation machinery. The presence of polysomes in the spores led us to evaluate the activity of the translation apparatus in these cells. We present evidence that there is ongoing transcription and translation in nongerminating yeast spores incubated in water at 30°C, suggesting that these activities could play a role in spore long term survival.Saccharomyces cerevisiae a/␣ diploid cells, when deprived of nitrogen in the presence of a nonmetabolizable carbon source, can enter a developmental program known as sporulation (1). Yeast sporulation consists of two overlapping processes, meiosis and spore formation. Meiosis leads to the synthesis of four haploid daughter cells that are the yeast gametes. Meanwhile, these gametes are embedded into a specialized structure, the spore, that can resist a variety of harsh treatments and allow the cell to survive drought, frost, heat, and chemical exposure (2). When favorable conditions return, the spore germinates and resumes its vegetative growth. This germination program includes the activation of cellular metabolism, extensive morphological changes, and reentry into the cell cycle followed by mating. One haploid cell of the a-mating type will encounter one haploid cell of the ␣-mating type, and their fusion will lead to the formation of a diploid cell, thus completing the sexual cycle (3). The development of germinating spores has been examined by electron microscopy (4 -7), and various physiological parameters have been characterized (8 -12). For instance, protein synthesis was reported to start 20 min and RNA transcription 70 min after the addition of glucose (13), therefore suggesting that spores must contain mRNA available for immediate translation. More recently, it has been confirmed that spore germination requires active protein synthesis during the 1st h and that it depends on the Ras signaling pathway (14). However, biochemical analysis was limited by the poor synchrony of germination of spores obtained by classical methods.In contrast to spore germination, about wh...

Global gene expression profiles for the growth phases of Trichophyton rubrum

“…The ability of fungal spores to store prepackaged mRNA has been reported in S. cerevisae, A. nidulans and N. crassa [19,20]. The prestored mRNA in conidia can be activated and translated rapidly in the presence of nutrients and soon after germination the stored mRNA decayed [21]. In a previous study, we found stored mRNA in T. rubrum conidia and this had similar expression characteristics to the mRNA of the Cluster I genes in this study [13].…”

The use of global transcriptional analysis to reveal the biological and cellular events involved in distinct development phases of Trichophyton rubrum conidial germination

“…These stored mRNA are primed for rapid activation and translation in the presence of nutrients. The decay of spores containing mRNA is induced soon after germination [34]. In this study, mRNA of genes in cluster I existed in spores before induction of germination and the expression levels of those genes were down-regulated immediately at the onset of germination.…”

Timing of Transcriptional Quiescence during Gametogenesis Is Controlled by Global Histone H3K4 Demethylation

“…The first descriptions of spore quiescence were obtained using strain backgrounds that exhibit moderately reduced sporulation efficiency and kinetics (Brengues et al, 2002; Hopper et al, 1974). To confirm that SK1 spores attain metabolic quiescence, we measured dissolved O 2 consumption rates of sporulating cells and found that terminally differentiated spores (36 hr post-induction) consume oxygen at ~4% the rate of cells at time 0 of time courses, demonstrating that mitochondrial respiration is dramatically downregulated during sporulation (Figure 2A).…”

“…Our microarray data presented in Figure 1D measured RNA produced from both DNA strands across the entire genome at high resolution. Although this data measured RNA from terminally sporulated cells at the 20 hr time point, as mRNA stability is dramatically upregulated during sporulation (Brengues et al, 2002), it nevertheless afforded us a means to evaluate this hypothesis. When we reassembled this data to construct a globally averaged protein coding gene transcript profile, we found, as expected, that the abundance of transcripts from this averaged transcript unit was reduced in jhd2Δ mutants, (Figure 4C).…”

“…Pioneering studies of Saccharomyces cerevisiae by Hopper et al (1974), later confirmed by Brengues et al (2002), first described spore dormancy by demonstrating dramatic reductions in mitochondrial respiration, transcription, and translation during sporulation. In spores, like in animal gametes, transcriptional dormancy, a phenomenon often referred to as “quiescence,” is counter-balanced by a dramatic increase in mRNA stability (Brengues et al, 2002; Hamatani et al, 2004; Schultz, 2002; Tadros and Lipshitz, 2009). Although the mechanisms underlying the transition to transcriptional quiescence in gametes remain unknown, given the global nature of the phenomenon, mechanisms that act throughout the genome irrespective of DNA sequence seem likely to be involved.…”