Two‐step, extensive alterations in the transcriptome from G0 arrest to cell division in Schizosaccharomyces pombe

Abstract

Body cells in multicellular organisms are in the G0 state, in which cells are arrested and terminally differentiated. To understand how the G0 state is maintained, the genes that are specifically expressed or repressed in G0 must be identified, as they control G0. In the fission yeast Schizosaccharomyces pombe, haploid cells are completely arrested under nitrogen source starvation with high viability. We examined the global transcriptome of G0 cells and cells on the course to resume vegetative growth. Approximately 20% of the transcripts of ~5000 genes increased or decreased more than fourfold in the two-step transitions that occur prior to replication. Of the top 30 abundant transcripts in G0, 23 were replaced by ribosome-and translation-related transcripts in the dividing vegetative state. Eight identified clusters with distinct alteration patterns of ~2700 transcripts were annotated by Gene Ontology. Disruption of 53 genes indicated that nine of them were necessary to support the proper G0 state. These nine genes included two C2H2 zinc finger transcription factors, a cyclin-like protein implicated in phosphorylation of RNA polymerase II, two putative autophagy regulators, a G-protein activating factor, and two CBS domain proteins, possibly involved in AMP-activated kinase.

Isp7 Is a Novel Regulator of Amino Acid Uptake in the TOR Signaling Pathway

“…The isp7 ϩ gene was originally isolated during a screen for genes that show increased transcription under nitrogen starvation conditions (41). ⌬isp7 mutant cells are viable but lose viability following heat shock during the stationary phase (42). We found that while overexpression of isp7 ϩ suppressed the sensitivity of ⌬tsc1/2 mutant cells to rapamycin, deletion of isp7 ϩ in the background of ⌬tsc1 or ⌬tsc2 cells resulted in double mutant cells that were unable to grow on proline plates (Fig.…”

“…2D) and the presence of feedback loop mechanisms may explain this paradoxical behavior of isp7 ϩ . Finally, disruption of isp7 ϩ results in an inability to acquire normal stationary-phase physiology, which is manifested by the inability of the cells to withstand heat shock under stationary (nondividing/G 0 -like) conditions (42,62). The long-term viability of nondividing cells is also known as chronological longevity (63).…”

Cut1/separase-dependent roles of multiple phosphorylation of fission yeast cohesin subunit Rad21 in post-replicative damage repair and mitosis

“…The FACS patterns shown in Figure 3A (right) indicate that the onset of DNA replication occurred around 6 hr, and the first mitosis at 8 to 10 hr, consistent with previous results. 24,25 The level of Rad21 in G 0 was comparable to that in VE and appeared to be hyper-phosphorylated. In our previous report, the level of Rad21 in G 0 was much lower than that in VE.…”

“…To determine whether Rad21 can be directly phosphorylated by Rad3/ATR, we performed an in vitro assay of Rad3/ATR tagged with GST and 25 and then released by adding nitrogen source at 26°C. The phosphorylation level of T147, S165 and S507 was assessed by phospho-specific antibodies.…”

“…A better understanding of the phosphorylation of 165 SP and 507 SP may help us to determine the role of cohesin in non-dividing G 0 cells. 25 While anti-phospho 165 S antibody detected only the hyper-upper band, anti-phospho 507 S antibody detected hypo-as well as hyper-phosphorylated forms, suggesting that the 507 S site is an initial phosphorylation site of…”