Direct Comparision of the Endocytic Routes of Fluorescently-Labelled Lipids and Transferrin
Intracellular trafficking of proteins during endocytosis has been extensively characterized. This process is mediated by vesicular carriers such as coated vesicles, sorting endosomes and late endosomes, all of which are composed primarily of membrane proteins and lipid. A central question in the endocytic process concerns the sorting of recycling components from lysosomally-directed components. An iterative fractionation model (Dunn and Maxfield, 1992; Dunn et al., 1989) and other current models of endocytic sorting (Linderman and Lauffenburger, 1988) propose that the geometry of the sorting endosome directs bulk membrane, including membrane-associated receptors, towards the recycling pathway while the volume content, consisting of the acid-released ligands, is lysosomally targetted. However, it is not known whether recycling membrane receptors follow bulk membrane flow or if these proteins are actively sorted from the lysosomally-directed material because of specific cytoplasmic tail sequences. The kinetics of movement of the bulk carrier, membrane lipids, will directly address this issue; a difference in the kinetics of lipid-traffic in relation to protein-traffic will provide evidence for mechanisms of selective protein transport or absence of difference will support the hypothesis that proteins follow ‘bulk’ membrane traffic.
KeywordsLate Endosome Endosomal Compartment Bulk Carrier Recycling Endosome Membrane Traffic
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