Actin/myosin function in intracellular vesicle transport processes

点击翻译按钮获取中文摘要

Directional membrane transport is the basis of eukaryotic cell organisation and polarisation. A combined transport along microtubule and actin filament tracks allows a specified delivery of molecules in space and time. The Rab11 GTPase is a master regulator of intracellular transport processes of the exocytic and recycling pathways and thereby a key function in the regulation of cell surface protein expression. Acting as a molecular switch, Rab11 builds distinct motor protein complexes at vesicle and endosomal membranes, which enable kinesin and dynein mediated fast and long-range transport along microtubules, as well as slower and local transport by myosin V actin motor proteins along actin filaments.Our recent discovery that Spir actin nucleators and myosin V assemble with Rab11 into a tripartite complex at vesicle membranes indicates a coordinated nucleation of actin filament tracks and myosin force generation on a subset of Rab11 vesicles. This enables actin/MyoV-driven motility in regions of the cell distal from the cortical actin network, such as in the oocyte cytoplasm and most likely in the central region of somatic cells. Based on live cell imaging data showing frequent nanotube formations of Spir/Rab11 vesicles, we propose a model in which the Spir and MyoV cooperation provides forces for vesicular morphological dynamics, which facilitates the attachment of vesicles to microtubule tracks for long-range transport.Novel genome editing technologies should be employed to specifically impair or modify Spir and MyoV functions in mouse fibroblast cells. Fluorescent protein tagged Spir, MyoV and Rab11 should be expressed under the control of their endogenous promoters. Modern fluorescence live cell imaging technologies will then enable us to monitor Rab11 vesicles and correlate morphological dynamics and motility to Spir and MyoV functions.The study proposed here should provide basic knowledge on the yet poorly understood functions of actin/myosin forces in intracellular vesicle transport processes and should thereby be elementary for subsequent mechanistic analysis of cell biological processes depending on these functions, such as the surface expression of adhesion molecules and growth factor receptors.