They also identify two functional defects in these tissues; reduced LDL uptake and impaired apical polarity of the hepatocytes. They also generate a simplified model of Rab5/early endosomal dynamics and suggest a role for Rab5 in vesicle fission as well as fusion. Although this model fits the available data quite well, it ignores several other key components of endosomal formation and maturation.
The authors also present the curious finding that while Rab5 depletion reduces both LDL uptake and endosome numbers, dynamin depletion only affects LDL uptake but not the number of endosomes. One possible explanation for this defect is that they quantify the presence of endosomes in this assay largely by EEA1 puncta. Since EEA1 is a Rab5 effector, it is possible that in the Rab5 depleted cells there is still a population of early endosomes, but that these are not detected by EEA1 staining.
Together this study presents a convincing picture for the role of Rab5 in endosomal dynamics, and highlight the important role of Rab5 in both endocytic pathways and in the establishment of polarity in vivo.
CitationZeigerer A, Gilleron J, Bogorad RL, Marsico G, Nonaka H, Seifert S, Epstein-Barash H, Kuchimanchi S, Peng CG, Ruda VM, Del Conte-Zerial P, Hengstler JG, Kalaidzidis Y, Koteliansky V, & Zerial M (2012). Rab5 is necessary for the biogenesis of the endolysosomal system in vivo. Nature, 485 (7399), 465-70 PMID: 22622570
Disclosure: I have received constructs and yeast strains from the Zerial laboratory in the past.
Rab5 Knockdown In Vivo by Dave Bridges is licensed under a Creative Commons Attribution 3.0 Unported License.