Proliferation and autophagic degradation of peroxisomes in Hansenula polymorpha

PhD ceremony: Mr. T. van Zutphen, 13.15 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: Proliferation and autophagic degradation of peroxisomes in Hansenula polymorpha

Promotor(s):prof. I.J. van der Klei

Faculty: Mathematics and Natural Sciences

A characteristic feature of eukaryotic cells is the presence of organelles. Yeast speciesare suitable model organisms for research on fundamental cellular processes like organelle formation and turnover. These unicellular organisms provide many advantages experimentally, like for instance the ease of genetic manipulation.

The research Tim van Zutphen described in his thesis was aimed at the biogenesis and turnover of peroxisomes in the yeast Hansenula polymorpha.

To discover which genes are expressed upon proliferation of peroxisomes, he performed a transcriptome analysis. Shortly upon induction of peroxisomes, the amount of transcript of the transcription factor Mpp1 increased almost 400 times. PEX genes involved in peroxisome formation were only marginally induced though.

Pex14 and Pex3, two peroxisomal membrane proteins, function in peroxisome formation and are also involved in organelle turnover. The protein Pex14 is part of a protein-complex involved in import of so-called matrix proteins into the peroxisome. Studies on a possible role in peroxisome degradation of the other proteins in this complex showed that Pex14 is the sole member involved in this process.

Pex3 is removed from the organelle upon peroxisome degradation. The effect of artificial Pex3 removal was analysed, which showed induction of organelle turnover. However the mode of degradation differed from known mechanisms.

A similar process was observed when peroxisomes were exposed to oxidative stress. These results of Van Zutphen suggest that damaging peroxisomes can induce organelle turnover.