TY - JOUR T1 - The Transmembrane Protein Semaphorin 6A Repels Embryonic Sympathetic Axons JF - The Journal of Neuroscience JO - J. Neurosci. SP - 2638 LP - 2648 DO - 10.1523/JNEUROSCI.20-07-02638.2000 VL - 20 IS - 7 AU - Xiao-Mei Xu AU - Daniel A. Fisher AU - Lijuan Zhou AU - Fletcher A. White AU - Sheldon Ng AU - William D. Snider AU - Yuling Luo Y1 - 2000/04/01 UR - http://www.jneurosci.org/content/20/7/2638.abstract N2 - Semaphorin 6A (Sema6A) (previously named Semaphorin VIa) is the originally described member of the vertebrate semaphorin class 6, a group of transmembrane semaphorins homologous to the insect semaphorin class 1. Although Sema-1a (previously named semaphorin I) has been implicated in axon guidance in insects, the function of Sema6A is currently unknown. We have expressed the extracellular domain of Sema6A in mammalian cells as either a monomeric or a dimeric fusion protein and tested for potential axon guidance effects on two populations of embryonic neurons in growth cone collapse and collagen matrix chemorepulsion assays. Sema6A was observed to induce growth cone collapse of sympathetic neurons with an EC50 of ∼200 pm, although a 10-fold higher (EC50 of ∼2 nm) concentration was necessary to induce growth cone collapse of dorsal root ganglion neurons. The activity of Sema6A is likely to depend on protein dimerization or oligomerization. Although Sema6A mRNA is expressed in complex patterns during embryonic development, it is strikingly absent from sympathetic ganglia. Sema6A is, however, expressed in areas avoided by sympathetic axons and in areas innervated by sympathetics, but before their arrival. Our results demonstrate that transmembrane semaphorins, like the secreted ones, can act as repulsive axon guidance cues. Our findings are consistent with a role for Sema6A in channeling sympathetic axons into the sympathetic chains and controlling the temporal sequence of sympathetic target innervation. ER -