title: A molecular mechanism that regulates medially oriented axonal growth of upper layer neurons in the developing neocortex.
abstract: During development, cortical neurons extend axons to their targets based on their laminar locations and cell types. Here we studied the molecular mechanism that regulates medially oriented axonal growth of upper layer neurons in the developing mouse cortex. Upper layer neurons were labeled with enhanced yellow fluorescent protein (EYFP) by in utero electroporation at E15.5. Cortical slices containing EYFP-labeled cells were dissected at E16, when axonal outgrowth from upper layer neurons is not initiated, and were cultured in an organotypic manner. After 3 days in culture, most labeled cells were found to extend axons medially in the same fashion as those observed in vivo. This oriented growth was disrupted when the lateral side of the cortical slice was removed, indicating that a laterally located repellent is involved in the medially oriented growth. Strikingly, the medially directed growth within the slices was reduced in the medium containing Semaphorin3A (Sema3A) or soluble form of Neuropilin-1 (Npn1), a receptor for Sema3A. Importantly, we found that Sema3A was expressed in a gradient from lateral-high to medial-low within the cortex, and callosal axons originating from upper layer neurons uniquely expressed Npn1. Consistent with these findings, ectopically expressed Sema3A repelled medially oriented elongation of upper layer cell axons in vivo. These results therefore suggest the operation of a repulsive mechanism for medially oriented axon growth of upper layer neurons, and further point to a role for a gradient expression of Sema3A in this directional axon growth along the mediolateral axis within the neocortex.
authors.affiliation: Laboratory of Cellular and Molecular Neurobiology, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan.
authors.forename: Hong
authors.initials: H
authors.lastname: Zhao
authors.forename: Takuro
authors.initials: T
authors.lastname: Maruyama
authors.forename: Yuki
authors.initials: Y
authors.lastname: Hattori
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Sugo
authors.forename: Hyota
authors.initials: H
authors.lastname: Takamatsu
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kumanogoh
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Shirasaki
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Yamamoto
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology* / Q000648:ultrastructure; D018274:Electroporation; D004622:Embryo, Mammalian / Q000033:anatomy & histology / Q000502:physiology; D005260:Female; D051379:Mice; D008810:Mice, Inbred C57BL; D019579:Neocortex / Q000166:cytology* / Q000196:embryology*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D039942:Neuropilin-1 / Q000378:metabolism; D011247:Pregnancy; D040121:Semaphorin-3A / Q000378:metabolism / Q000494:pharmacology; D046509:Tissue Culture Techniques
chemical_list: D040121:Semaphorin-3A; D039942:Neuropilin-1