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

CONDE C; SIRI SO; ARIAS CI

Workshop; Workshop Actualizations in membrane trafficking in health and disease (EMBO); 2016

SARA (Smad Anchor for Receptor Activation) plays a crucial role in Rab5-mediated endocytosis in cell lines localizing to early endosomes where it regulates morphology and function. It has been shown that SARA overexpression causes enlargement of early endosomes, and significantly delays transferrin recycling (Hu et al., 2002). Moreover, SARA has been proposed as a novel vesicle-tethering molecule capable of interacting with membrane proteins such as rhodopsin and syntaxin 3 in axonemal vesicles (Chuang et al., 2007), suggesting that SARA may play a role in neuronal morphogenesis. Therefore, we analyzed the role of SARA during neuronal development and tested whether it functions as a regulator of endocytic trafficking of selected axonal and membrane proteins.Using neuronal cultures prepared from rat embryonic hippocampi we revealed that, in neurons in stages 2 and 3, SARA is evenly distributed throughout the cell body, minor neurites, axon and growth cones.Suppression of SARA perturbs the appearance of juxtanuclear endocytic recycling compartments and the neurons show long axons with large growth cones, displaying much longer and branched axon-like neurites (Tau-1 +) than control cells. Identical results were observed in hippocampal pyramidal neurons cultured from SARA-KO mice. Furthermore, surface distribution of the cell adhesion molecule L1 in axons and the fusion of vesicles containing transferring receptor in dendrites were increased in neurons where SARA was silenced. Conversely, SARA overexpression generated large early endosomes and reduced neurite outgrowth. Our findings suggest a significant contribution of SARA to key aspects of neuronal development, including neurite formation.We acknowledge grants from CONICET and FONCyT.