In Schizosaccharomyces pombe, rad24 and rad25 have been identified to be homologous to mammalian 14-3-3 genes and found to be involved in many cellular events, including checkpoint and meiosis. In the present study, we present evidences that Rad24 and Rad25 act as negative regulators of Byr2 (mitogen-activated protein kinase [MAPK] kinase kinase). Overexpression of rad24 or rad25 reduced mating and sporulation in homothallic wild-type cells. In contrast, the mating and sporulation efficiency of rad24-or rad25-null cells was higher than that of wild-type cells. Deletion of rad24 or rad25 increased sporulation efficiency in ras1-null diploid cells but not in byr2-, ste4-, byr1-, and spk1-null cells. Rad24 and Rad25 had no effect on the activity of constitutively active Byr1 S214DT218D . Rad24 and Rad25 bound to both the N-terminal and the C-terminal domains of Byr2 when these bacterially expressed proteins were examined. The formation of complexes in vivo between Byr2 and either Rad24 or Rad25 was also confirmed by immunocoprecipitation. Furthermore, we showed negative regulation of Byr2 by Rad25, by monitoring the mRNA level of mam2, which is regulated by both the Ras1/MAPK pathway and ste11, in various combinations of mutants. In addition, the cellular localization of Byr2 in living cells was observed by using fusion to green fluorescent protein. Byr2 was mainly localized in the cytoplasm during vegetative growth and then concentrated at the plasma membrane in response to nitrogen starvation. Deletion of rad24 or rad25 fastened the timing of Byr2 translocation. Our results are consistent with the hypothesis that one of the roles of 14-3-3 is to keep Byr2 in the cytoplasm and to affect the timing of Byr2 translocation in response to sexual developmental signal.

The cAMP pathway in Schizosaccharomyces pombe is the major nutrient sensing pathway to initiate sexual development when opposite mating type cells exist. We identified moc1-moc4 as genes that overcome a partially sterile S. pombe strain due to an elevation of cAMP. When we compared the strength of inducing ability of sexual development in the same S. pombe strain, Moc1 had highest, Moc2 had lowest, and both Moc3 and Moc4 had intermediate effects. Moc1/Sds23 and Moc2/Ded1 are known to be a potential regulator of M-phase progression and an essential RNA helicase, respectively. While Moc4 was found to be identical with a Zn-finger protein Zfs1, Moc3 (SPAC821.07c) was a novel protein containing a Zn-finger (Zn(2)-Cys(6)) motif. Deletion mutant of the moc3 gene was constructed and its disruptant was found to be lower in mating efficiency and formed aberrant asci. In addition, unexpectedly, a moc3 disruptant was sensitive to CaCl(2) and DNA damaging agents such as MMS and UV. Those phenotypes were opposite to the phenotypes observed in a zfs1 disruptant, and quite different from the ones in a moc1 disruptant. Moc3 localized in the nucleus as observed for Zfs1. Moc3 bound with Moc4/Zfs1 weakly in the two hybrid system, but no other combination of Moc(s) bound each other in the same analysis. Thus, Moc3 is not only involved in sexual development, but also in ascus formation and DNA integrity in an independent manner with Moc1 and Moc2 in S. pombe.

The sexual differentiation of Schizosaccharomyces pombe is controlled by many cellular components which have not been fully characterized. We isolated a gene called msa2 as a multi-copy suppressor of a sporulation abnormal mutant (sam1). Msa2p is identical with Nrd1p which has been characterized as a factor that blocks the onset of sexual differentiation. The yeast two-hybrid system was used to identify Cpc2p, a fission yeast homolog of the RACK1 protein, that interacted with Msa2p/Nrd1p. We confirmed that Msa2p/Nrd1p interacted with Cpc2p in S. pombe cells. An epistatic analysis of msa2/nrd1 and cpc2 suggests that Msa2p/Nrd1p was an upstream regulator for Cpc2p. A localization analysis of Cpc2p and Msa2p/Nrd1p indicates that both proteins were predominantly localized in the cytoplasm. The interaction of negative regulator Msa2p/Nrd1p with positive regulator Cpc2p suggests a new regulatory circuit in the sexual differentiation of S. pombe.

Sexual differentiation in the fission yeast Schizosaccharomyces pombe is triggered by nutrient starvation or by the presence of mating pheromones. We identified a novel gene, msa1, which encodes a 533-aa putative RNA-binding protein that inhibits sexual differentiation. Disruption of the msa1 gene caused cells to hypersporulate. Intracellular levels of msa1 RNA and Msa1 protein diminished after several hours of nitrogen starvation. Genetic analysis suggested that the function of msa1 is independent of the cAMP pathway and stress-responsive pathway. Deletion of the ras1 gene in diploid cells inhibited sporulation and in haploid cells decreased expression of mating-pheromone-induced genes such as mei2, mam2, ste11, and rep1; simultaneous deletion of msa1 reversed both phenotypes. Overexpression of msa1 decreased activated Ras1Val17 -induced expression of mam2. Phenotypic hypersporulation was similar between cells with deletion of only rad24 and both msa1 and rad24, but simultaneous deletion of msa1 and msa2/nrd1 additively increased hypersporulation. Therefore, we suggest that the primary function of Msa1 is to negatively regulate sexual differentiation by controlling the expression of Ste11-regulated genes, possibly through the pheromone-signaling pathway.

The functional impact and cellular context of mosaic structural variants (mSVs) in normal tissues is understudied. Utilizing Strand-seq, we sequenced 1,133 single cell genomes from 19 human donors of increasing age, revealing a heterogeneous mSV landscape in hematopoietic stem and progenitor cells (HSPCs). While mSV clonal expansions are confined to individuals over 60, de novo mSV formation occurs consistently across age, frequently leading to megabase-scale segmental aneuploidies. Cells harboring subclonal mosaicism show evidence for increased mSV formation. To enable high resolution cell-typing of each Strand-seq library, we generated single-cell MNase-seq reference datasets for eight distinct HSPCs. Subclonal mSVs frequently exhibit enrichment in myeloid progenitors, and single-cell multiomic analysis suggests that these mSVs result in recurrent dysregulation of pathways related to proliferation and metabolism, including Ras signaling and lipid metabolism. The comprehensive mSV landscape identified in this study implicates mSVs in cell type specific molecular phenotypes, establishing a foundation for deciphering links between mSVs, aging, and disease risk.