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First published online March 8, 2006
doi: 10.1242/10.1242/jcs.02893

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The return of the peroxisome

¹ Department of Cellular Protein Chemistry and Academic Biomedical Centre, Utrecht University, Padualaan 8, NL-3548 CH Utrecht, The Netherlands
² Laboratory of Cell Biology, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands

View larger version (198K): [in a new window]   Fig. 1. Birth of peroxisomes in a mouse dendritic cell. Ultra-thin section of a high-pressure frozen D1 cell showing clusters of electron-dense peroxisomes (P) that are often positioned adjacent to a lamella (L). Arrows indicate areas of membrane continuity between the endoplasmic reticulum (ER) and the lamellae (Geuze et al., 2003; Tabak et al., 2003). Bar, 200 nm.

View larger version (31K): [in a new window]   Fig. 2. Model for the roles of Pex3p and Pex19p in the insertion of proteins into the peroxisomal membrane. According to the model, the insertion of Pex3p into the ER membrane and the subsequent recruitment of Pex19p to the membrane leads to the formation of a pre-peroxisomal organelle. At this stage, cytosolic Pex19p can also engage in peroxisomal membrane protein (PMP) import by binding peroxisomal membrane proteins and targeting these to the pre-peroxisomal membrane. By an unknown process, the PMP cargo is released from the membrane-associated Pex19p and is inserted into the membrane. Once PMP insertion is complete, matrix proteins begin to be imported, resulting in the functional maturation of the pre-peroxisome into a peroxisome.

View larger version (47K): [in a new window]   Fig. 3. Peroxisome formation in S. cerevisiae. The top two rows show a time course of peroxisome formation induced by expression of Pex3-YFP (green) (based on Hoepfner et al., 2005); the ER is visualized by constitutive expression of Sec63-CFP (red); blue false colour shows the phase contrast. Schematics below display the events that are taking place. At the onset of the induction experiment, no Pex3-YFP signal is present (0). 60 minutes later, the first detectable weak Pex3-YFP signal localizes to structures containing the perinuclear ER marker Sec63-CFP (60). At 90 minutes after induction, Pex3-YFP starts to concentrate into dots, which are frequently localized at the periphery of the ER (90). At 120 minutes after induction, the Pex3-YFP is localized exclusively to dot-like structures that are significantly brighter and no longer overlap with the Sec63-CFP signal (120). Finally, 5-10 individual Pex3-YFP dots per cell are discernible and show no apparent ER colocalization but instead mostly localize to the cell cortex (300).