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 (Smad Anchor for Receptor Activation) plays a crucial role in Rab5-mediatedendocytosis in cell lines localizing to early endosomes where it regulates morphologyand function. It has been shown that SARA overexpression causes enlargement ofearly endosomes, and significantly delays transferrin recycling (Hu et al., 2002).Moreover, SARA has been proposed as a novel vesicle-tethering molecule capableof interacting with membrane proteins such as rhodopsin and syntaxin 3 in axonemalvesicles (Chuang et al., 2007), suggesting that SARA may play a role in neuronalmorphogenesis. Therefore, we analyzed the role of SARA during neuronaldevelopment and tested whether it functions as a regulator of endocytic trafficking ofselected 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 recyclingcompartments and the neurons show long axons with large growth cones, displayingmuch longer and branched axon-like neurites (Tau-1 +) than control cells. Identicalresults were observed in hippocampal pyramidal neurons cultured from SARA-KOmice. Furthermore, surface distribution of the cell adhesion molecule L1 in axonsand the fusion of vesicles containing transferring receptor in dendrites wereincreased in neurons where SARA was silenced. Conversely, SARA overexpressiongenerated large early endosomes and reduced neurite outgrowth. Our findingssuggest a significant contribution of SARA to key aspects of neuronal development,including neurite formation