Functional diversity of Robo receptor immunoglobulin domains promotes distinct axon guidance decisions.
Recognition molecules of the immunoglobulin (Ig) superfamily control axon guidance in the developing nervous system. Ig-like domains are among the most widely represented protein domains in the human genome, and the number of Ig superfamily proteins is strongly correlated with cellular complexity. In Drosophila, three Roundabout (Robo) Ig superfamily receptors respond to their common Slit ligand to regulate axon guidance at the midline: Robo and Robo2 mediate midline repulsion, Robo2 and Robo3 control longitudinal pathway selection, and Robo2 can promote midline crossing. How these closely related receptors mediate distinct guidance functions is not understood. We report that the differential functions of Robo2 and Robo3 are specified by their ectodomains and do not reflect differences in cytoplasmic signaling. Functional modularity of Robo2's ectodomain facilitates multiple guidance decisions: Ig1 and Ig3 of Robo2 confer lateral positioning activity, whereas Ig2 confers promidline crossing activity. Robo2's distinct functions are not dependent on greater Slit affinity but are instead due in part to differences in multimerization and receptor-ligand stoichiometry conferred by Robo2's Ig domains. Together, our findings suggest that diverse responses to the Slit guidance cue are imparted by intrinsic structural differences encoded in the extracellular Ig domains of the Robo receptors.
Evans
Timothy A
TA
Department of Neuroscience, University of Pennsylvania School of Medicine, 421 Curie Boulevard, Philadelphia, PA 19104, USA.
Bashaw
Greg J
GJ
D000818:Animals; D030801:Animals, Genetically Modified; D001369:Axons / Q000502:physiology; D019521:Body Patterning; D002490:Central Nervous System / Q000196:embryology; D004330:Drosophila / Q000196:embryology* / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D017344:Genes, Insect; D006801:Humans; D007136:Immunoglobulins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D011971:Receptors, Immunologic / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000097905:Roundabout Proteins
D029721:Drosophila Proteins; D007136:Immunoglobulins; D009419:Nerve Tissue Proteins; D011971:Receptors, Immunologic; D011994:Recombinant Proteins; D000097905:Roundabout Proteins; C421243:Robo2 protein, Drosophila; C421244:robo3 protein, Drosophila; C066819:sli protein, Drosophila