Dynamin 1 is important for microtubule organization and stabilization in glomerular podocytes

Dynamin 1 is a neuronal endocytic protein that participates in vesicle formation by scission of invaginated membranes. Dynamin 1 is also expressed in the kidney; however, its physiological significance to this organ remains unknown. Here, we show that dynamin 1 is crucial for microtubule organization and stabilization in glomerular podocytes. By immunofluorescence and immunoelectron microscopy, dynamin 1 was concentrated at microtubules at primary processes in rat podocytes. By immunofluorescence of differentiated mouse podocytes (MPCs), dynamin 1 was often colocalized with microtubule bundles, which radially arranged toward periphery of expanded podocyte. In dynamin 1-depleted MPCs by RNAi, alpha-tubulin showed a dispersed linear filament-like localization, and microtubule bundles were rarely observed. Furthermore, dynamin 1 depletion resulted in the formation of discontinuous, short acetylated alpha-tubulin fragments, and the decrease of microtubule-rich protrusions. Dynamins 1 and 2 double-knockout podocytes showed dispersed acetylated alpha-tubulin and rare protrusions. In vitro, dynamin 1 polymerized around microtubules and cross-linked them into bundles, and increased their resistance to the disassembly-inducing reagents Ca(2+)and podophyllotoxin. In addition, overexpression and depletion of dynamin 1 in MPCs increased and decreased the nocodazole resistance of microtubules, respectively. These results suggest that dynamin 1 supports the microtubule bundle formation and participates in the stabilization of microtubules

Met and the epidermal growth factor receptor act cooperatively to regulate final nephron number and maintain collecting duct morphology

Ureteric bud (UB) branching during kidney development determines the final number of nephrons. Although hepatocyte growth factor and its receptor Met have been shown to stimulate branching morphogenesis in explanted embryonic kidneys, loss of Met expression is lethal during early embryogenesis without obvious kidney abnormalities. Metfl/fl;HoxB7-Cre mice, which lack Met expression selectively in the UB, were generated and found to have a reduction in final nephron number. These mice have increased Egf receptor expression in both the embryonic and adult kidney, and exogenous Egf can partially rescue the branching defect seen in kidney explants. Metfl/fl;HoxB7-Cre;wa-2/wa-2 mice, which lack normal Egfr and Met signaling, exhibit small kidneys with a marked decrease in UB branching at E14.5 as well as a reduction in final glomerular number. These mice developed progressive interstitial fibrosis surrounding collecting ducts with kidney failure and death by 3-4 weeks of age. Thus, in support of previous in vitro findings, Met and the Egf receptor can act cooperatively to regulate UB branching and mediate maintenance of the normal adult collecting duct