Origin and growth of peroxisomes in yeast: The molecular mechanism of peroxisome formation in yeast

Peroxisomes are single membrane bound organelles, which occur in most eukaryotic cells. Their size, number and function, highly depend on the organism in which they occur. The origin of peroxisomes is debated for decades. Two different models have been proposed: the organelles form by fission of pre-existing peroxisomes or originate from another organelle, the endoplasmic reticulum (ER).The work described in this thesis strongly supports the model that peroxisomes are not formed from the ER. Instead they grow and divide like mitochondria, other important cell organelles.

Lipids are the building blocks of the peroxisomal membrane. Because peroxisomes lack a membrane lipid synthesizing machinery, lipids have to be transported to the organelles from other cellular sources. Studies described in this thesis revealed for the first time that the ER and vacuoles may play a central role in peroxisome membrane biogenesis, similar as recently described for mitochondria. The ER and vacuoles form membrane contact sites with peroxisomes, where most likely lipids are transferred from one organellar membrane to the other, resulting in peroxisomal membrane expansion.