Managing intracellular transport

Abstract

Formation and normal function of neuronal synapses are intimately dependent on the delivery to and removal of biological materials from synapses by the intracellular transport machinery. Indeed, defects in intracellular transport contribute to the development and aggravation of neurodegenerative disorders. Despite its importance, regulatory mechanisms underlying this machinery remain poorly defined. We recently uncovered a phosphorylation-regulated mechanism that controls FEZ1-mediated Kinesin-1-based delivery of Stx1 into neuronal axons. Using C. elegans as a model organism to investigate transport defects, we show that FEZ1 mutations resulted in abnormal Stx1 aggregation in neuronal cell bodies and axons. This phenomenon closely resembles transport defects observed in neurodegenerative disorders. Importantly, diminished transport due to mutations of FEZ1 and Kinesin-1 were concomitant with increased accumulation of autophagosomes. Here, we discuss the significance of our findings in a broader context in relation to regulation of Kinesin-mediated transport and neurodegenerative disorders.

Keywords: FEZ1; Kinesin; Munc18; SNARE; Syntaxin; autophagy; axonal transport; neurodegeneration; synapse; transport defects.

Figure 1. FEZ1/UNC-76 serves as a motor adaptor for presynaptic cargo. (A) Kinesin-1/UNC-116 binds Stx1/UNC-64-containing transport vesicles via the adaptor FEZ1/UNC-76 forming a complex with Stx1/UNC-64 and Munc18/UNC-18. Dephosphorylation of FEZ1/UNC-76 releases the cargo from the motor. (B) In the absence of Munc18/UNC-18, Stx1/UNC-64 is not efficiently transported to the synapse. (C) Defects in adaptor function may result in transport abnormalities leading to cargo degradation and neurodegeneration.