title: Ephrin-B3 reverse signaling through Grb4 and cytoskeletal regulators mediates axon pruning.
abstract: It has been suggested that ephrin-B proteins have receptor-like roles in the control of axon pathfinding by repulsion, although it is largely unknown how the reverse signals are coupled to downstream intracellular molecules and how they induce cytoskeletal reorganization at the axon terminal. We found that ephrin-B3 (EB3) was able to function as a repulsive guidance receptor and mediate stereotyped pruning of murine hippocampal mossy fiber axons during postnatal development. Targeted intracellular point mutants showed that axon pruning requires tyrosine phosphorylation-dependent reverse signaling and coupling to the SH2/SH3 adaptor protein Grb4 (also known as Nckbeta/Nck2). Furthermore, we found that the second SH3 domain of Grb4 is required and sufficient for axon pruning/retraction by mediating interactions with Dock180 and PAK to bring about guanine nucleotide exchange and signaling downstream of Rac, respectively. Our results reveal a previously unknown pathway that controls axon pruning and elucidate the biochemical mechanism by which ephrin-B reverse signals regulate actin dynamics to bring about the retraction of growth cones.
authors.affiliation: Department of Developmental Biology, Kent Waldrep Center for Basic Research on Nerve Growth and Regeneration, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9133, USA.
authors.forename: Nan-Jie
authors.initials: NJ
authors.lastname: Xu
authors.forename: Mark
authors.initials: M
authors.lastname: Henkemeyer
mesh_terms: D000199:Actins / Q000502:physiology; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology*; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D018920:Coculture Techniques; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000502:physiology*; D036389:Ephrin-B3 / Q000235:genetics / Q000502:physiology*; D055879:Gene Knock-In Techniques; D020439:Growth Cones / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D019599:Mossy Fibers, Hippocampal / Q000378:metabolism / Q000502:physiology*; D015513:Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D014161:Transduction, Genetic
chemical_list: D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D003598:Cytoskeletal Proteins; D036389:Ephrin-B3; C117758:Nck2 protein, mouse; D015513:Oncogene Proteins