A cell surface interaction network of neural leucine-rich repeat receptors

Abstract

Background: The vast number of precise intercellular connections within vertebrate nervous systems is only partly explained by the comparatively few known extracellular guidance cues. Large families of neural orphan receptor proteins have been identified and are likely to contribute to these recognition processes but due to the technical difficulty in identifying novel extracellular interactions of membrane-embedded proteins, their ligands remain unknown.

Avidity-based Extracellular Interaction Screening (AVEXIS) for the Scalable Detection of Low-affinity Extracellular Receptor-Ligand Interactions

“…The assay is not generally suitable for multipass membrane proteins such as ion transporters or pumps since they are unlikely to be correctly folded outside the context of a plasma membrane. We have applied this to a variety of different systems and have successfully expressed extracellular proteins from zebrafish 3,16,18 , human, mouse and P. falciparum for interaction screens.…”

“…The frequency at which interactions are detected depends upon the content of the protein library being screened. As a guide to the reader, a screen of >30,000 interactions within the zebrafish immunoglobulin superfamily resulted in 188 positives -a frequency of 0.6% 3,16,18 . A very rapid check that can be performed to verify any positive hits is to determine whether the interaction can be detected in both bait-prey orientations; that is, can the same interaction be detected irrespective of whether the binding proteins are present as either a bait or a prey.…”

Fine tuning cellular recognition

“…19 Strikingly, a recent screen performed in zebrafish aimed at identifying cell surface proteins involved in protein-protein interactions has discovered several LRRTM family members as interactors with Robo receptors, amongst which were Lrrc24, Elfn1 and LRRTM1. 20 The high similarity between the domainstructure of LRT and LRRTM proteins expressed in the nervous systems of mice and zebrafish, coupled with the ability of some of the LRRTM proteins to bind Robo family members, implies that LRT's function in coordinating muscle/tendon adhesion through association with Robo might be an evolutionary conserved mechanism important for synapse formation.…”

“…15 These receptors contribute to the targeting specificity of peripheral axons to distinct types of a trans-membrane domain (thus called LRRTM proteins) are important for trans-synaptic signaling and synapse formation. 19,20 These include previously characterized proteins such as the Netrin-G-ligand (NGL) proteins NGL-2 and NGL-3, who have been shown to interact with Netrin-G and the LAR receptor protein phosphatase, respectively, 21,22 and members of the Fibronectin Leucine Rich Transmembrane (FLRT) family of proteins. The screen performed in mice searched for synaptogenic proteins expressed in a co-culture of neurons and fibroblasts.…”

Amigo Adhesion Protein Regulates Development of Neural Circuits in Zebrafish Brain

“…LRR domains are protein-protein interaction motifs that have been implicated in development and plasticity of fiber tracts, recognition of axon targets, synaptogenesis, and disorders of the nervous system. Slit proteins (Slit 1-3), Trk receptors (TrkA, TrkB, and TrkC), and Nogo receptor 1 (NgR1) are among the most studied LRR proteins in the nervous system development (2,3). AMIGO (amphoterin-induced gene and open reading frame) was found by ordered differential display as a transcript up-regulated in rat hippocampal neurons that extend neurites upon ligation of the transmembrane receptor RAGE (receptor for advanced glycation end products) by amphoterin (HMGB1; high mobility group box-1) or by anti-RAGE antibodies (4).…”