Peroxisome formation and dynamics in yeast

PhD ceremony: Ms. R. Saraya, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: Peroxisome formation and dynamics in yeast

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

Faculty: Mathematics and Natural Sciences

Peroxisomes are characteristic organelles of eukaryotic cells. These organelles may perform various functions dependent on cell type and environmental needs For long, there has been a strong debate in the field of how peroxisomes are formed.The aim of the research was to obtain further insights into the process of peroxisome formation (fission, inheritance and peroxisome formation from the ER) with emphasis on proteins involved in these processes, using the yeast Hansenula polymorpha as principal model organism.

We demonstrate that in H. polymorpha peroxisome fission is the major pathway of peroxisome proliferation. Deletion of DNM1 resulted in a single peroxisome which formed long protrusions in the newly formed bud that did not divide until during cytokinesis. We also show that Dnm1 and Vps1 are not required for peroxisome formation from the ER.We next studied the role of Pex11 family members in peroxisome reintroduction from the ER. Pex25, but not Pex11 and Pex11c, were observed to play a role in this process as peroxisomes could not be reintroduced in pex3 pex25 strain. Additionally our studies indicate that Ypt7 (a protein involved in vacuolar fusion) is involved in peroxisome fission.

We also analyzed peroxisome inheritance in H. polymorpha. In this study we have identified Inp1- and Inp2- related proteins in 18 budding yeast species, indicating that both proteins are highly conserved in yeast. Additionally, we demonstrated that the identified putative H. polymorpha Inp2 is localized to peroxisomes and the deletion of INP2 resulted in a defect in peroxisome inheritance to bud cells.