hettemae

Dr Ewald Hettema

Reader in Molecular Cell Biology


Tel: 0114 222 2732
Email: e.hettema@sheffield.ac.uk

Research

Research Precis

fig1My group aims to improve understanding of the molecular mechanisms underlying peroxisome dynamics at the cellular level.

Cells contain a large number of distinct membrane bound organelles. These compartments rely on complex machineries to acquire and maintain their unique composition and function. We are studying one of these organelles, the peroxisome. Lack of functional peroxisomes results in a deficiency of a large number of enzymatic reactions and a disorder called Zellweger (ZS-) or cerebro-hepato-renal syndrome. Proteins required for peroxisome formation are called peroxins and these have been found mutated in ZS patients.

Peroxisomes multiply by growth and division.

The endoplasmic reticulum (ER) provides peroxisomes with membrane constituents allowing these organelles to grow, after which the organelles divide and distribute between mother and daughter cell. The number of peroxisomes per cell is influenced by intracellular and extracellular factors and these can induce proliferation or breakdown. How these processes are regulated and integrated into cellular metabolism is poorly understood.

fig2Fig 2A. Peroxisomes multiply and are subsequently transported to the newly forming daughter cell via an actin-myosin-based process. Approximately half the number of the peroxisomes are anchored to the periphery of mother cells and remain there. These opposing processes ensure peroxisome segregation with high fidelity. Fig 2B. Peroxisomes can be induced to proliferate under conditions of high requirement for these organelles. A subsequent shift to conditions where peroxisomes are superfluous induces their rapid breakdown by autophagy. Selective breakdown of peroxisomes is named pexophagy.

Genetic model organisms to study peroxisome dynamics and functioning

We and others have been using Saccharomyces cerevisiae as our model system and mutants have been identified that are disturbed in various aspects of peroxisome dynamics. These mutants have been instrumental in unravelling the underlying mechanisms of peroxisome formation, multiplication and segregation. We have recently focussed on the peroxisomal membrane protein Pex3. Lack of Pex3 results in a complete absence of peroxisomal structures. We have now found that Pex3 is also involved in peroxisome segregation during cell division and peroxisome turnover. It does this by binding of process-specific factors and therefore may act as a scaffold for the regulation of peroxisome dynamics.

fig3

Fig 3 shows. Mutants in S.cerevisiae cells are gene deletion mutants. Mutant phenotypes in D. melanogaster S2 cells were created by temporary inactivation of genes with RNAi. Blue circumference of yeast cells is artificially coloured bright field image. Nuclei are stained with DAPI in S2 cells and artificially coloured blue in images.

More recently we have extended our studies into other model organisms including the fruit fly Drosophila melanogaster, the slime mould Dictyostelium discoideum and human cells. For instance, a genome-wide RNAi screen in Drosophila cells identified many of the known proteins involved in peroxisome formation and peroxisome multiplication. Interestingly, we also identified several new genes that appear to be involved in formation and regulation of peroxisome dynamics. We use molecular cell biological approaches including live-cell imaging, genome-wide RNAi screens, yeast genetics, proteomics and protein-protein interaction studies to characterise the function of these new proteins.

Although our main interest is in a fundamental understanding of peroxisome dynamics and its role in peroxisome functioning, we are also following up on lines of research that potentially have medical implications.

Research Keywords

Eukaryotic cell biology, yeast genetics, Saccharomyces cerevisiae, peroxisomes, autophagy, peroxisome biogenesis disorders

I welcome applications from self-funded prospective home and international PhD students; see examples of possible projects below. You can apply for a PhD position in MBB here.

Contact me at e.hettema@sheffield.ac.uk for further information.

Examples of self-funded PhD projects:

Development of genome editing tools for use in non-model organisms with biotechnological potential

Construction of synthetic organelles for biotechnology

Investigations into the molecular mechanisms of organelle movement and inheritance

Characterisation of peroxisome fission and formation

Fungal extracellular vesicle formation

Teaching

Level 3 Modules

MBB342 Genetics of Cell Growth and Division

Level 1 Modules

MBB164 Molecular Biology

Career History

Career History

  • 2014 - present: Reader in Molecular Cell Biology, Dept. Molecular Biology and Biotechnology, University of Sheffield
  • 2008 - 2014: Wellcome Trust Senior Research Fellow in Basic Biomedical Science at University of Sheffield
  • 2004 - 2008: Wellcome Trust Career Development Fellow at University of Sheffield
  • 2000 - 2004: Postdoctoral Reserach Associate, MRC LMB, Cambridge
  • 1998 - 2000: Postdoctoral Reserach Associate, University of Amsterdam
  • 1998: PhD, University of Amsterdam








































Publications

Journal articles

Conference proceedings papers

  • Al-hejjaj M, Watts D & Hettema EH (2016) Attempt to develop a CRISPR system for use in Dictyostelium discoideum.. MOLECULAR BIOLOGY OF THE CELL, Vol. 27 RIS download Bibtex download