Figure 2.

Schematic representation of mechanisms for peroxisome formation in mammalian cells. Peroxisome formation by growth and division follows a multistep maturation process involving peroxisomal membrane remodelling and elongation, membrane constriction and final scission. Membrane expansion requires peroxisome-ER contact (red line) and lipid transfer (red arrow), generating a membrane compartment which imports newly synthesised PMPs and matrix proteins. De novo peroxisome formation: In the absence of pre-existing peroxisomes, preperoxisomal vesicles can be generated at the ER (EDV) and mitochondria (MDV), which may fuse and mature into new import-competent peroxisomes. These newly formed peroxisomes will further multiply by growth and division. In the presence of peroxisomes, preperoxisomal vesicles may fuse with growing or existing peroxisomes to supply certain proteins and lipids. EDV, ER-derived vesicles; MDV, mitochondria-derived vesicles; newly formed peroxisomes are coloured in light green.