Jack Fransen is an associate professor at the Cell Biology Department of the Radboud University Medical Centre since 1992. His background is in Cell Biology / Electron Microscopy. His group has been working on intracellular transport and apical and basolateral sorting of proteins in polarized cells. The group focusses mainly on the ultrastructural aspects using immunoelectron microscopy and confocal techniques. The work has concentrated on the vesicle bound machinery involved in these processes with special emphasis on the function of Rab proteins (i.e. Rab6 isoforms and Rab21) and specific protein tyrosine phosphatases (i.e. PTP-SL) in the regulation of vesicular traffic at the Golgi and post-Golgi level. Recently topic has switched to imaging in space and time of proteins and small molecules involved in localized energy supply in cells.The group also started to implement 3D and 4D imaging within the department and is in charge of a part of the equipment within the Microscopic Imaging Centre of the RIMLS (RIMLS-MIC).