Role of Dynamin in Polarization
The large GTPase dynamin is a regulatory mechanoenzyme that participates in nascent vesicle formation and actin cytoskeletal regulation. The function of dynamin has been extensively investigated in non-polarized mammalian cells and is involved in an array of cellular processes including cytokinesis, cell migration and centrosome cohesion. Studies conducted in our laboratory with Shibire, the dynamin orthologue in Drosophila, have shown it to also function in cellularization, a process that appears to occur simultaneously with creating membrane polarity. However, dynamin’s role in membrane polarization remains largely undefined.
Membrane polarity is intimately linked to the establishment and maintenance of intercellular junctions that partition the plasma membrane (PM) into apical (AP) and basolateral (BL) and the vectorial transports that create concentration gradients across the junctions. The assembly of these junctions, which are collectively called the apical junctional complex (AJC) and are composed of adherens junctions (AJs) and tight junctions (TJs), occurs during cell-cell adhesion and is linked to cytoskeletal reorganization. Because dynamin appears to be involved in polarization and is a known modulator of many actin-binding proteins, we hypothesize that dynamin is a central player in the assembly and maintenance of these junctions in fully polarized epithelial cells. Here, it is likely that dynamin has many regulatory roles distinct and in addition to its widely accepted mechanochemical function in membrane trafficking.
Figure: A live cell image of an MDCK cell transiently transfected with GPI-GFP (green) and RFP-GalT (red). In a fully polarized MDCK cell, GPI-GFP trafficks to the apical surface while RFP-GalT remains in the Golgi. (see movie- GPI-GFP trafficking, which shows traffic from the golgi to the apical surface of a fully polarized cell after a 2hr block at 20C.)
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