How is an organelle formed?
Prof. Henk Tabak (UU) spent the last decade of his career solving a particularly nagging issue:
how a cellular compartment (or organelle), called a peroxisome, was formed. Organelles
cannot be made from its individual lipid and protein components alone. As a rule organelles
can only be derived from a pre-existing organelle.
Autonomous organelles like mitochondria are generated from growth and division of preexisting compartments, but contain their own protein import machineries indicative of their
endosymbiotic origin. Organelles of the endomembrane pathway like the Golgi, however, rely
on the ER (endoplasmic reticulum) for their formation and protein import. Peroxisomes defied
the odds as they combine elements of both strategies.
Henk Tabak’s quest started with world-renowned electron microscopist Hans Geuze. They
found strange membranous structures surrounding peroxisomes in certain mouse cells that
were in fact continuous with the membrane of the ER. This key observation initiated the work
that followed. Henk Tabak returned to working with yeast and followed peroxisome formation
in living cells using real-time fluorescence microscopy. Together with Dominic Hoepfner he
discovered the existence of a new membrane-trafficking route starting from the ER that is
responsible for the formation of peroxisomes (Cell, 2005). He completed his triumph together
with Adabella van der Zand to show that the ER is step-wise remodeled into biochemically
different vesicles that fuse to ultimately form a new peroxisomal compartment (Cell, 2012).
By providing comprehensive evidence that peroxisomes constitute a dynamic endomembrane
system that originates from the ER and by defining molecular mechanisms underlying the
spatiotemporal dynamics of the peroxisomal endomembrane system, Henk Tabak has made a
major impact on one of the basic paradigms of cellular organization that has found its way into
the textbooks already.
Source: Ineke Braakman (UU)