Involvement of SARA in regulating membrane traffic during axonal and dendritic growth

CONDE, CECILIA; ARIAS, CRISTINA ISABEL; SEBASTIÁN OMAR SIRI

la serena

Workshop; EMBO WORKSHOP Actualizations in Membrane Trafficking in Health and Disease; 2016

EMBO

SARA (SmadAnchor for Receptor Activation) plays a crucial role in Rab5-mediatedendocytosis in cell lines localizing to early endosomes where it regulatesmorphology and function. It has been shown that SARA overexpression causesenlargement of early endosomes, and significantly delays transferrin recycling(Hu et al., 2002). Moreover, SARA has been proposed as a novelvesicle-tethering molecule capable of interacting with membrane proteins suchas rhodopsin and syntaxin 3 in axonemal vesicles (Chuang et al., 2007),suggesting that SARA may play a role in neuronal morphogenesis. Therefore, weanalyzed the role of SARA during neuronal development and tested whether itfunctions as a regulator of endocytic trafficking of selected axonal andmembrane proteins.Using neuronal cultures prepared from rat embryonic hippocampi we revealedthat, in neurons in stages 2 and 3, SARA is evenly distributed throughout thecell body, minor neurites, axon and growth cones.Suppression of SARA perturbs the appearance of juxtanuclear endocytic recyclingcompartments and the neurons show long axons with large growth cones,displaying much longer and branched axon-like neurites (Tau-1 +) than controlcells. Identical results were observed in hippocampal pyramidal neuronscultured from SARA-KO mice. Furthermore, surface distribution of the celladhesion molecule L1 in axons and the fusion of vesicles containing transferringreceptor in dendrites were increased in neurons where SARA was silenced.Conversely, SARA overexpression generated large early endosomes and reducedneurite outgrowth. Our findings suggest a significant contribution of SARA tokey aspects of neuronal development, including neurite formation.