FLRT2 and FLRT3 act as repulsive guidance cues for Unc5-positive neurons

Abstract

Netrin-1 induces repulsive axon guidance by binding to the mammalian Unc5 receptor family (Unc5A-Unc5D). Mouse genetic analysis of selected members of the Unc5 family, however, revealed essential functions independent of Netrin-1, suggesting the presence of other ligands. Unc5B was recently shown to bind fibronectin and leucine-rich transmembrane protein-3 (FLRT3), although the relevance of this interaction for nervous system development remained unclear. Here, we show that the related Unc5D receptor binds specifically to another FLRT protein, FLRT2. During development, FLRT2/3 ectodomains (ECDs) are shed from neurons and act as repulsive guidance molecules for axons and somata of Unc5-positive neurons. In the developing mammalian neocortex, Unc5D is expressed by neurons in the subventricular zone (SVZ), which display delayed migration to the FLRT2-expressing cortical plate (CP). Deletion of either FLRT2 or Unc5D causes a subset of SVZ-derived neurons to prematurely migrate towards the CP, whereas overexpression of Unc5D has opposite effects. Hence, the shed FLRT2 and FLRT3 ECDs represent a novel family of chemorepellents for Unc5-positive neurons and FLRT2/ Unc5D signalling modulates cortical neuron migration.

Placental labyrinth formation in mice requires endothelial FLRT2–UNC5B signaling

“…S2A,B) and examination of β-galactosidase expression in these mice. In agreement with previously published results, we observed abundant β-galactosidase expression in a population of neurons and the epicardium (Yamagishi et al, 2011;Müller et al, 2011), but not in embryonic endothelial cells ( Fig. 2A-C…”

“…5A). FLRT2 is known to act as a repulsive cue on neurons through binding to UNC5B and UNC5D (Yamagishi et al, 2011). Among the UNC5 proteins, only UNC5B is indispensable for embryonic development, and Unc5b knockouts are lethal at approximately E12.5, similar to the Flrt2 ΔEHC genotype (Lu et al, 2004;Navankasattusas et al, 2008).…”

“…5B). To evaluate whether the repulsive mechanism of interaction between FLRT2 and UNC5B acts in endothelial cells in the same way as in neuronal cells (Yamagishi et al, 2011;Seiradake et al, 2014), a Transwell assay and a stripe assay were performed in HUVECs with recombinant FLRT2 and UNC5B proteins. Compared with vehicle only, FLRT2 significantly decreased migration of HUVECs in the Transwell assay and resulted in repulsion of the cells away from stripes containing the recombinant protein ( Fig.…”

“…Fibronectin leucine-rich transmembrane protein 2 (FLRT2) is a member of the fibronectin leucine-rich transmembrane (FLRT) family of proteins, which act as repulsive ligands of the UNC5 receptor family and as chemorepellents for neurons (Lacy et al, 1999;Yamagishi et al, 2011;Seiradake et al, 2014). Outside of the nervous system, FLRT2 is expressed in the epicardium, and its global knockout leads to reduced thickness of the ventricular myocardium, suggesting a role for FLRT2 in heart morphogenesis (Müller et al, 2011).…”

Yeast Two-Hybrid Screening for Proteins that Interact with the Extracellular Domain of Amyloid Precursor Protein

“…During embryonic development, FLRT3 can be shed and release the ectodomain. Then this ectodomain can serve as a guidance cue for the axons of Unc5-positive neurons [18]. APP has been reported to mediate axon guidance [6].…”