title: Involvement of Hedgehog and FGF signalling in the lamprey telencephalon: evolution of regionalization and dorsoventral patterning of the vertebrate forebrain.
abstract: Dorsoventral (DV) specification is a crucial step for the development of the vertebrate telencephalon. Clarifying the origin of this mechanism will lead to a better understanding of vertebrate central nervous system (CNS) evolution. Based on the lamprey, a sister group of the gnathostomes (jawed vertebrates), we identified three lamprey Hedgehog (Hh) homologues, which are thought to play central signalling roles in telencephalon patterning. However, unlike in gnathostomes, none of these genes, nor Lhx6/7/8, a marker for the migrating interneuron subtype, was expressed in the ventral telencephalon, consistent with the reported absence of the medial ganglionic eminence (MGE) in this animal. Homologues of Gsh2, Isl1/2 and Sp8, which are involved in the patterning of the lateral ganglionic eminence (LGE) of gnathostomes, were expressed in the lamprey subpallium, as in gnathostomes. Hh signalling is necessary for induction of the subpallium identity in the gnathostome telencephalon. When Hh signalling was inhibited, the ventral identity was disrupted in the lamprey, suggesting that prechordal mesoderm-derived Hh signalling might be involved in the DV patterning of the telencephalon. By blocking fibroblast growth factor (FGF) signalling, the ventral telencephalon was suppressed in the lamprey, as in gnathostomes. We conclude that Hh- and FGF-dependent DV patterning, together with the resultant LGE identity, are likely to have been established in a common ancestor before the divergence of cyclostomes and gnathostomes. Later, gnathostomes would have acquired a novel Hh expression domain corresponding to the MGE, leading to the obtainment of cortical interneurons.
authors.affiliation: Laboratory for Evolutionary Morphology, Center for Developmental Biology, RIKEN, 2-2-3 Minatojima-minami, Kobe 650-0047, Japan.
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Sugahara
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Aota
authors.forename: Shigehiro
authors.initials: S
authors.lastname: Kuraku
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Murakami
authors.forename: Yoko
authors.initials: Y
authors.lastname: Takio-Ogawa
authors.forename: Shigeki
authors.initials: S
authors.lastname: Hirano
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kuratani
mesh_terms: D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning / Q000235:genetics / Q000502:physiology*; D004625:Embryo, Nonmammalian; D005260:Female; D005346:Fibroblast Growth Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D007798:Lampreys / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D016548:Prosencephalon / Q000196:embryology* / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D013687:Telencephalon / Q000196:embryology* / Q000378:metabolism; D014714:Vertebrates / Q000196:embryology / Q000235:genetics / Q000378:metabolism
chemical_list: D053823:Hedgehog Proteins; D005346:Fibroblast Growth Factors