3 research outputs found
Autophagy at a crossroads:Investigating the regulation and functions of autophagy
Get PDFOur cells must recycle their «waste» to stay healthy, work properly, and adapt to survive. Autophagy is a cellular recycling process that helps cells break down and reuse their damaged, harmful, or unnecessary parts. Cells create membranous «bags» called autophagosomes to sequester the unwanted material. Once the «waste» is bagged, autophagosomes fuse with lysosomes, delivering their contents inside these acidic organelles. Lysosomes act like the cell's digestive system enzymatically degrading unwanted material like proteins, sugars, and fats into basic «building blocks». These are then used as fuel or recycled to build new parts for the cell. When autophagy is defective, unwanted material builds up, which can cause various diseases, including neurodegenerative disorders and cancer.This thesis explores how the formation of autophagosomes is regulated. We studied the role of specific motor proteins, called dynamins, in controlling the transport of a key autophagy protein, Atg9. We also identified enzymes that regulate autophagy and are involved in adding or removing a special molecular tag named ubiquitin to proteins. This thesis also explores how degrading specific proteins by autophagy is important for the cell to adapt its metabolism when nutrient levels change. For this, we developed a new experimental tool that helps identify proteins degraded by autophagy at a specific time in baker’s yeast. We found proteins, including metabolic enzymes, that may be specifically degraded to adapt to nitrogen scarcity in this model organism.Our findings improve our understanding of the regulation of autophagy and its role in metabolic adaptations
Cell polarity protein Spa2 coordinates Chs2 incorporation at the division site in budding yeast
Get PDFDeposition of additional plasma membrane and cargoes during cytokinesis in eukaryotic cells must be coordinated with actomyosin ring contraction, plasma membrane ingression and extracellular matrix remodelling. The process by which the secretory pathway promotes specific incorporation of key factors into the cytokinetic machinery is poorly understood. Here, we show that cell polarity protein Spa2 interacts with actomyosin ring components during cytokinesis. Spa2 directly binds to cytokinetic factors Cyk3 and Hof1. The lethal effects of deleting the SPA2 gene in the absence of either Cyk3 or Hof1 can be suppressed by expression of the hypermorphic allele of the essential chitin synthase II (Chs2), a transmembrane protein transported on secretory vesicles that makes the primary septum during cytokinesis. Spa2 also interacts directly with the chitin synthase Chs2. Interestingly, artificial incorporation of Chs2 into the cytokinetic machinery allows the localisation of Spa2 at the site of division. In addition, increased Spa2 protein levels promote Chs2 incorporation at the site of division and primary septum formation. Our data indicate that Spa2 is recruited to the cleavage site to co-operate with the secretory vesicle system and particular actomyosin ring components to promote the incorporation of Chs2 into the so-called ‘ingression progression complexes’ during cytokinesis in budding yeast.</div
Ingression Progression Complexes Control Extracellular Matrix Remodelling during Cytokinesis in Budding Yeast.
Get PDFEukaryotic cells must coordinate contraction of the actomyosin ring at the division site together with ingression of the plasma membrane and remodelling of the extracellular matrix (ECM) to support cytokinesis, but the underlying mechanisms are still poorly understood. In eukaryotes, glycosyltransferases that synthesise ECM polysaccharides are emerging as key factors during cytokinesis. The budding yeast chitin synthase Chs2 makes the primary septum, a special layer of the ECM, which is an essential process during cell division. Here we isolated a group of actomyosin ring components that form complexes together with Chs2 at the cleavage site at the end of the cell cycle, which we named 'ingression progression complexes' (IPCs). In addition to type II myosin, the IQGAP protein Iqg1 and Chs2, IPCs contain the F-BAR protein Hof1, and the cytokinesis regulators Inn1 and Cyk3. We describe the molecular mechanism by which chitin synthase is activated by direct association of the C2 domain of Inn1, and the transglutaminase-like domain of Cyk3, with the catalytic domain of Chs2. We used an experimental system to find a previously unanticipated role for the C-terminus of Inn1 in preventing the untimely activation of Chs2 at the cleavage site until Cyk3 releases the block on Chs2 activity during late mitosis. These findings support a model for the co-ordinated regulation of cell division in budding yeast, in which IPCs play a central role
