Peroxisome fission in Hansenula polymorpha requires Mdv1 and Fis1, two proteins also involved in mitochondrial fission

We show that Mdv1 and Caf4, two components of the mitochondrial fission machinery in Saccharomyces cerevisiae, also function in peroxisome proliferation. Deletion of MDV1, CAF4 or both, however, had only a minor effect on peroxisome numbers at peroxisome-inducing growth conditions, most likely related to the fact that Vps1--and not Dnm1--is the key player in peroxisome fission in this organism. In contrast, in Hansenula polymorpha, which has only a Dnm1-dependent peroxisome fission machinery, deletion of MDV1 led to a drastic reduction of peroxisome numbers. This phenotype was accompanied by a strong defect in mitochondrial fission. The MDV1 paralog CAF4 is absent in H. polymorpha. In wild-type H. polymorpha, cells Dnm1-mCherry and green fluorescent protein (GFP)-Mdv1 colocalize in spots that associate with both peroxisomes and mitochondria. Furthermore, Fis1 is essential to recruit Mdv1 to the peroxisomal and mitochondrial membrane. However, formation of GFP-Mdv1 spots--and related to this normal organelle fission--is strictly dependent on the presence of Dnm1. In dnm1 cells, GFP-Mdv1 is dispersed over the surface of peroxisomes and mitochondria. Also, in H. polymorpha mdv1 or fis1 cells, the number of Dnm1-GFP spots is strongly reduced. These spots still associate to organelles but are functionally inactive.