A conserved role for Syntaxin-1 in pre- and post-commissural midline axonal guidance in fly, chick, and mouse

Abstract

Axonal growth and guidance rely on correct growth cone responses to guidance cues. Unlike the signaling cascades that link axonal growth to cytoskeletal dynamics, little is known about the crosstalk mechanisms between guidance and membrane dynamics and turnover. Recent studies indicate that whereas axonal attraction requires exocytosis, chemorepulsion relies on endocytosis. Indeed, our own studies have shown that Netrin-1/Deleted in Colorectal Cancer (DCC) signaling triggers exocytosis through the SNARE Syntaxin-1 (STX1). However, limited in vivo evidence is available about the role of SNARE proteins in axonal guidance. To address this issue, here we systematically deleted SNARE genes in three species. We show that loss-of-function of STX1 results in pre- and post-commissural axonal guidance defects in the midline of fly, chick, and mouse embryos. Inactivation of VAMP2, Ti-VAMP, and SNAP25 led to additional abnormalities in axonal guidance. We also confirmed that STX1 loss-of-function results in reduced sensitivity of commissural axons to Slit-2 and Netrin-1. Finally, genetic interaction studies in Drosophila show that STX1 interacts with both the Netrin-1/DCC and Robo/Slit pathways. Our data provide evidence of an evolutionarily conserved role of STX1 and SNARE proteins in midline axonal guidance in vivo, by regulating both pre- and post-commissural guidance mechanisms.

Syntaxin-1/TI-VAMP SNAREs interact with Trk receptors and are required for neurotrophin-dependent outgrowth

“…Together with previous studies showing that various SNARE complex proteins are necessary for the signaling of guidance molecules exerting either chemoattraction (e.g. Netrin1, [ 17 , 18 ]) or chemorepulsion (e.g., class III Semaphorins, [ 69 ]; Slits/Robo [ 76 ], our findings on neurotrophins—another family of extracellular factors that mediates axonal growth—support the notion that the association of receptor complexes with specific sets of SNARE proteins that mediate exocytosis or endocytosis is a general mechanism by which neurotrophic factors and guidance cues exert their effects to promote axonal guidance and growth.…”

Guiding synaptic plasticity: Novel roles for netrin‐1 in synaptic plasticity and memory formation in the adult brain

“…The DCC intracellular domain interacts with the E3 ubiquitin ligase, TRIM9, which binds synaptic vesicle SNARE proteins, such as the target (t)-SNARE SNAP25 (Li et al 2001;Winkle et al 2014;Plooster et al 2017). Netrin-1/DCC signalling also activates the t-SNARE, syntaxin-1 (Ros et al 2018), which forms a complex with SNAP25 and synaptobrevin-2 that is required for depolarization-mediated vesicular fusion at synapses (Sudhof & Rothman, 2009). These findings raise the intriguing possibility that presynaptic loss of DCC may impair neurotransmitter release, thereby attenuating basal synaptic transmission to the extent that it may not be sufficient to induce LTP (Isaac et al 1995;Emptage et al 2003;Glasgow et al 2019a).…”

Syntaxin-1 is necessary for UNC5/Netrin-1-dependent macropinocytosis and chemorepulsion

“…In addition, we have found that Stx1 is required for the repulsion of commissural axons (Ros et al, 2018). Here, we first investigated whether Stx1 interacts with the chemorepulsive Netrin-1 receptors UNC5B and UNC5C, which are important in the control of the repulsive response of axonal tracts during cerebellar development (Alcantara et al, 2000).…”

“…It has been shown that clathrin-dependent endocytosis drives repulsive growth cone responses to Semaphorin 3A (Tojima et al, 2010). It is also known that Ephrin-A2, Sonic hedgehog (Shh) and Slit2 stimulate in dorsal root ganglion, retinal ganglion cell and commissural growth cones, a specific type of clathrin-independent endocytosis of large structures known as macropynocitosis (Guo et al, 2012;Jurney et al, 2002;Kabayama et al, 2009;Ros et al, 2018). Interestingly, the vesicle SNARE VAMP-2 mediates the sorting of Neuropilin-1/Plexin-A1 receptors, which is required for repulsion by Semaphorin 3A (Zylbersztejn et al, 2012).…”