Article

Overexpression of autophagy-related genes inhibits yeast filamentous growth.

Department of Molecular, Cellular and Developmental Biology and Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109-2216, USA.
Autophagy (Impact Factor: 11.42). 11/2007; 3(6):604-9. DOI: 10.4161/auto.4784
Source: PubMed

ABSTRACT Under conditions of nitrogen stress, the budding yeast S. cerevisiae initiates a cellular response involving the activation of autophagy, an intracellular catabolic process for the degradation and recycling of proteins and organelles. In certain strains of yeast, nitrogen stress also drives a striking developmental transition to a filamentous form of growth, in which cells remain physically connected after cytokinesis. We recently identified an interrelationship between these processes, with the inhibition of autophagy resulting in exaggerated filamentous growth. Our results suggest a model wherein autophagy mitigates nutrient stress, and filamentous growth is responsive to the degree of this stress. Here, we extended these studies to encompass a phenotypic analysis of filamentous growth upon overexpression of autophagy-related (ATG) genes. Specifically, overexpression of ATG1, ATG3, ATG7, ATG17, ATG19, ATG23, ATG24 and ATG29 inhibited filamentous growth. From our understanding of autophagy in yeast, overexpression of these genes does not markedly affect the activity of the pathway; thus, we do not expect that this filamentous growth phenotype is due strictly to diminished nitrogen stress in ATG overexpression mutants. Rather, these results highlight an additional undefined regulatory mechanism linking autophagy and filamentous growth, possibly independent of the upstream nitrogen-sensing machinery feeding into both processes.

0 Bookmarks
 · 
109 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: The budding yeast Saccharomyces cerevisiae can respond to nutritional and environmental stress by implementing a morphogenetic program wherein cells elongate and interconnect, forming pseudohyphal filaments. This growth transition has been studied extensively as a model signaling system with similarity to processes of hyphal development that are linked with virulence in related fungal pathogens. Classic studies have identified core pseudohyphal growth signaling modules in yeast; however, the scope of regulatory networks that control yeast filamentation is broad and incompletely defined. Here, we address the genetic basis of yeast pseudohyphal growth by implementing a systematic analysis of 4,909 genes for overexpression phenotypes in a filamentous strain of S. cerevisiae. Our results identify 551 genes conferring exaggerated invasive growth upon overexpression under normal vegetative growth conditions. This cohort includes 79 genes lacking previous phenotypic characterization. Pathway enrichment analysis of the gene set identifies networks mediating MAPK signaling and cell cycle progression. In particular, overexpression screening suggests that nuclear export of the osmoresponsive mitogen-activated protein kinase (MAPK) Hog1p may enhance pseudohyphal growth. The function of nuclear Hog1p is unclear from previous studies, but our analysis using a nuclear-depleted form of Hog1p is consistent with a role for nuclear Hog1p in repressing pseudohyphal growth. Through epistasis and deletion studies, we also identified genetic relationships with the G2 cyclin Clb2p and phenotypes in filamentation induced by S-phase arrest. In sum, this work presents a unique and informative resource towards understanding the breadth of genes and pathways that collectively constitute the molecular basis of filamentation.
    Genetics 02/2013; DOI:10.1534/genetics.112.147876 · 4.87 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The pseudohyphal growth response is a dramatic morphological transition and presumed foraging mechanism wherein yeast cells form invasive and surface-spread multicellular filaments. Pseudohyphal growth has been studied extensively as a model of conserved signaling pathways controlling stress responses, cell morphogenesis, and fungal virulence in pathogenic fungi. The genetic contribution to pseudohyphal growth is extensive, with at least 500 genes required for filamentation; as such, pseudohyphal growth is a complex trait, and linkage analysis is a classical means to dissect the genetic basis of a complex phenotype. Here, we implemented linkage analysis by crossing each of two filamentous strains of Saccharomyces cerevisiae (Σ1278b and SK1) with an S288C-derived non-filamentous strain. We then assayed meiotic progeny for filamentation and mapped allelic linkage in pooled segregants by whole-genome sequencing. This analysis identified linkage in a cohort of genes, including the negative regulator SFL1, which we find contains a premature stop codon in the invasive SK1 background. The S288C allele of the polarity gene PEA2, encoding Leu409 rather than Met, is linked with non-invasion. In Σ1278b, the pea2-M409L mutation results in decreased invasive filamentation and elongation, diminished activity of a Kss1p MAPK pathway reporter, decreased unipolar budding, and diminished binding of the polarisome protein Spa2p. Variation between SK1 and S288C in the mitochondrial inner membrane protein Mdm32p at residues 182 and 262 impacts invasive growth and mitochondrial network structure. Collectively, this work identifies new determinants of pseudohyphal growth, while highlighting the coevolution of protein complexes and organelle structures within a given genome in specifying complex phenotypes.
    PLoS Genetics 08/2014; 10(8):e1004570. DOI:10.1371/journal.pgen.1004570 · 8.17 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The budding yeast Saccharomyces cerevisiae responds to nutritional stress through the regulated activities of signaling pathways mediating autophagy and other conserved cellular processes. Autophagy has been studied intensely in yeast, where over 30 autophagy-related genes have been identified with defined roles enabling the formation of autophagic vesicles and their subsequent trafficking to the central yeast vacuole. Much less, however, is known regarding the regulatory mechanisms through which autophagy is integrated with other yeast stress responses. Nitrogen limitation initiates autophagy and pseudohyphal growth in yeast, the latter being a fascinating stress response characterized by the formation of multicellular chains or filaments of elongated cells. An increasing body of evidence suggests an interrelationship between processes responsive to nitrogen stress with cAMP-dependent PKA and the TOR kinase complex acting as key regulators of autophagy, pseudohyphal growth, and endocytosis. In this review, we will summarize our current understanding of the regulatory events controlling these processes. In particular, we explore the interplay between autophagy, polarized pseudohyphal growth, and to a lesser extent endocytosis, and posit that the integrated response of these processes in yeast is a critical point for further laboratory experimentation as a model of cellular responses to nitrogen limitation throughout the Eukaryota.
    12/2012; 1(3):263-83. DOI:10.3390/cells1030263

Full-text (2 Sources)

Download
15 Downloads
Available from
Jun 2, 2014