The role of exocyst complex in the insertion of new membrane at the growth cone at inicial stages of axon formation

Congreso; Neuroscience 2017; 2017

Society of Neuroscience

The initial signals and pathways that determine neuron polarity are largely unknown, placing the mechanisms underlying the axon formation as the scope of our investigation. Two interconnected process are essential for axon formation: Axonal specification and rapid plasma membrane outgrowth. The exocytic pathways that function to translocate membrane structural elements to the plasmalemma, occurs by regulated non secretory exocytosis. It has been shown in hippocampal neurons that the axolemmal expansion occurs by the insertion of plasmmalemal precursor vesicles (PPVs) at the growth cone, a process regulated by the neurotrophic factor Insulin like growth factor type 1 (IGF1). Also the assembly of the machinery related to the fusion process is highly regulated trough several steps, including the exocyst complex and SNARE proteins. Expression silencing of three proteins involved in the SNARE family (VAMP4, Syntaxin6 and SNAP23) repressed axonal outgrowth and the establishment of neuronal polarity, by inhibiting IGF-1 receptor exocytotic polarized insertion, necessary for neuronal polarization. The exocyst complex is an octameric well conserved complex and a important candidate for the regulation of PPV fusion into the plasmmalea. Its biochemical composition is still unknown in neurons. We have previously reported that IGF-1 activates the GTP-binding protein TC10, which triggers translocation to the plasma membrane of the exocyst component exo70 at the distal axon and growth cone and this can trigger exocyst complex assembly. Our results show that several proteins of the exocyst complex are present at hippocampal cultures in vitro in early stages of development and present at growth cone. Moreover, Sec3, one of the conserved protein components in exocyst complex, seem to have an important role as a membrane marker of vesicle fusion at hippocampal neurons at the growth cone. The implication of silencing Sec3 and some of the excoyst complex proteins in two polarity models such as hippocampal cultures in vitro and in utero electroporation of cortical neurons are currently our main research study.