Research Westermann Group: The Molecular Machinery of Mitochondrial Dynamics, Inheritance, and Architecture
Each type of eukaryotic cell has a characteristic three-dimensional structure. Maintenance of its architecture and duplication during cell division depend on active transport of organelles along the cytoskeleton and continuous fission and fusion of intracellular membranes. Mitochondria are essential organelles which are often located at sites of high energy consumption in the cell. They cannot be formed de novo, but have to be inherited during cell division. Positioning and transport of mitochondria and maintenance of mitochondrial function are controlled by the cytoskeleton and depend on fusion and fission of their membranes. These processes are functionally linked to the machinery that maintains the complex architecture of mitochondrial inner membrane cristae. We use the budding yeast Saccharomyces cerevisiae and other model organisms to study these processes. By studying mitochondrial morphology and inheritance we can learn a lot about many different aspects of organellar biogenesis, such as partitioning of organelles during cell division, transport of membranes along the cytoskeleton, intracellular membrane fusion, cellular aging and much more.
Cellular logistics and functional genomics of mitochondrial inheritance in yeast (DFG We 2174/5-1 and 5-2)
Mitochondria are essential organelles of eukaryotic cells. They must be inherited upon cell division and are often positioned at specific intracellular sites. These processes depend on interaction of mitochondria with the cytoskeleton. We use budding yeast Saccharomyces cerevisiae as a simple eukaryotic model organism to study mitochondrial transport, inheritance and intracellular positioning. Our previous work revealed that anterograde bud-directed mitochondrial transport is mediated by the myosin motor protein Myo2. It is assumed that transport of mitochondria back into the mother cell occurs by attachment of the organelle to actin cables and retrograde actin cable flow. Furthermore, actin polymerization and dynamics on the mitochondrial surface together with retention of mitochondria by attachment to specific sites at the cell cortex contribute to the cellular logistics of mitochondrial distribution. However, only little is known about the specific genes and proteins involved in these processes. The proposed research involves functional analyses of known components, development of microscopy-based cytological assays, and functional genomic approaches to obtain a comprehensive picture of the molecular mechanisms and genetic pathways contributing to mitochondrial motility and inheritance in yeast.
Genetic and cellular basis of mitochondrial genome inheritance and maintenance in yeast (DFG We 2174/6-1)
Inheritance and maintenance of the mitochondrial genome play an important role for the energy metabolism of eukaryotic cells. Dysfunctions cause neurodegenerative diseases and symptoms of aging. The genetic and cellular basis of mitochondrial genome inheritance and its repair and quality control mechanisms are only poorly understood. Yeast Saccharomyces cerevisiae is an excellent model organism to study these processes, as mitochondrial respiration is facultative dispensable, and yeast is ideally suited for genetic and systems biology approaches. The current proposal has two major aims: 1. A systematic genome-wide analysis of the interaction of nuclear genes with wild type or mutant mitochondrial DNA (mtDNA); 2. the development and establishment of methods to study mtDNA inheritance at the single-cell level. For the first aim, we will perform synthetic genetic arrays (SGA) using mutant libraries covering the entire yeast genome that are confronted with various mtDNA variants. These experiments will systematically reveal the genes that are important for mtDNA inheritance, maintain functional mtDNA in the long-term and protect it against damage. These include components mediating replication, recombination, and partitioning of mtDNA and factors involved in protection, repair, and elimination of defective mtDNA. For the second aim, we will fluorescently label mtDNA nucleoids in heteroplasmic cells containing different mitochondrial genomes. This will be done by tagging of nucleoid proteins with fluorescent proteins or fluorescence in situ hybridization (FISH), respectively. Furthermore, we will examine the involvement of mitochondrial or cytosolic proteins in transport or partitioning of mtDNA. This can be analyzed by colocalization in light and electron microscopy or fluorescence cross-correlation spectroscopy (FCCS). In a later phase of the project both major aims will be combined by functional analysis of the components newly discovered in the genome-wide screens employing the newly established methods. These experiments promise a detailed understanding of the genetic and cellular pathways contributing to inheritance and maintenance of the mitochondrial genome in a simple eukaryotic cell.
Deutsche Projektzusammenfassung: DFG GEPRIS
Selected Reviews
Braun, R.J. and Westermann, B. (2017). With the help of MOM: mitochondrial contributions to cellular quality control. Trends Cell Biol. 27:441-452. PubMed.
Westermann, B. und Geimer, S. (2016). Elektronenmikroskopie - Einblicke in die Nanowelt der Zellen. Spektrum (Universität Bayreuth) 12 (2), 44-47. PDF (German).
Westermann, B. (2015). The mitochondria-plasma membrane contact site. Curr. Opin. Cell Biol. 35:1-6. PubMed.
Klecker, T., Böckler, S., and Westermann, B. (2014). Making connections: interorganelle contacts orchestrate mitochondrial behavior. Trends Cell Biol. 24:537-545. PubMed.
Westermann, B. (2014). Mitochondrial inheritance in yeast. Biochim. Biophys. Acta 1837:1039-1046. PubMed.
Westermann, B. (2012). Bioenergetic role of mitochondrial fusion and fission. Biochim. Biophys. Acta 1817:1833-1838. PubMed.
Braun, R.J. and Westermann, B. (2011). Mitochondrial dynamics in yeast cell death and aging. Biochem. Soc. Trans. 39:1520-1526. PubMed.
Westermann, B. (2010). Mitochondrial fusion and fission in cell life and death. Nat. Rev. Mol. Cell Biol. 11:872-884. PubMed.
Westermann, B. (2010). Mitochondrial dynamics in model organisms: What yeasts, worms and flies have taught us about fusion and fission of mitochondria. Semin. Cell Dev. Biol. 21:542-549. PubMed.
Westermann, B. (2008). Molecular machinery of mitochondrial fusion and fission. J. Biol. Chem. 283:13501-13505 (Review). PubMed.
Sequence Information for mtGFP Plasmids