Department of Molecular Biosciences, The University of Kansas, 1200 Sunnyside Avenue, 5049 Haworth Hall, Lawrence, KS 66045, USA.
Development. 2023 Apr 1;150(7). doi: 10.1242/dev.201031. Epub 2023 Apr 4.
In the polarity/protrusion model of growth cone repulsion from UNC-6/netrin, UNC-6 first polarizes the growth cone of the VD motor neuron axon via the UNC-5 receptor, and then regulates protrusion asymmetrically across the growth cone based on this polarity. UNC-6 stimulates protrusion dorsally through the UNC-40/DCC receptor, and inhibits protrusion ventrally through UNC-5, resulting in net dorsal growth. Previous studies showed that UNC-5 inhibits growth cone protrusion via the flavin monooxygenases and potential destabilization of F-actin, and via UNC-33/CRMP and restriction of microtubule plus-end entry into the growth cone. We show that UNC-5 inhibits protrusion through a third mechanism involving TOM-1/tomosyn. A short isoform of TOM-1 inhibited protrusion downstream of UNC-5, and a long isoform had a pro-protrusive role. TOM-1/tomosyn inhibits formation of the SNARE complex. We show that UNC-64/syntaxin is required for growth cone protrusion, consistent with a role of TOM-1 in inhibiting vesicle fusion. Our results are consistent with a model whereby UNC-5 utilizes TOM-1 to inhibit vesicle fusion, resulting in inhibited growth cone protrusion, possibly by preventing the growth cone plasma membrane addition required for protrusion.
在 UNC-6/netrin 生长锥排斥的极性/突出模型中，UNC-6 通过 UNC-5 受体首先使 VD 运动神经元轴突的生长锥极化，然后根据这种极性使生长锥不对称地突出。UNC-6 通过 UNC-40/DCC 受体刺激背侧突出，通过 UNC-5 抑制腹侧突出，导致净背侧生长。先前的研究表明，UNC-5 通过黄素单加氧酶和 F-肌动蛋白的潜在不稳定以及 UNC-33/CRMP 抑制微管进入生长锥来抑制生长锥的突起。我们表明 UNC-5 通过涉及 TOM-1/tomosyn 的第三种机制抑制突起。TOM-1 的短异构体抑制 UNC-5 下游的突起，而长异构体具有促进突起的作用。TOM-1/tomosyn 抑制 SNARE 复合物的形成。我们表明 UNC-64/syntaxin 是生长锥突起所必需的，这与 TOM-1 在抑制囊泡融合中的作用一致。我们的结果与以下模型一致，即 UNC-5 利用 TOM-1 抑制囊泡融合，从而抑制生长锥突起，可能是通过阻止突起所需的生长锥质膜添加。
