title: The Shark Alar Hypothalamus: Molecular Characterization of Prosomeric Subdivisions and Evolutionary Trends.
abstract: The hypothalamus is an important physiologic center of the vertebrate brain involved in the elaboration of individual and species survival responses. To better understand the ancestral organization of the alar hypothalamus we revisit previous data onScOtp,ScDlx2/5,ScTbr1,ScNkx2.1 expression and Pax6 immunoreactivity jointly with new data onScNeurog2,ScLhx9,ScLhx5, andScNkx2.8expression, in addition to immunoreactivity to serotonin (5-HT) and doublecortin (DCX) in the catsharkScyliorhinus canicula, a key species for this purpose since cartilaginous fishes are basal representatives of gnathostomes (jawed vertebrates). Our study revealed a complex genoarchitecture for the chondrichthyan alar hypothalamus. We identified terminal (rostral) and peduncular (caudal) subdivisions in the prosomeric paraventricular and subparaventricular areas (TPa/PPa and TSPa/PSPa, respectively) evidenced by the expression pattern of developmental genes likeScLhx5(TPa) and immunoreactivity against Pax6 (PSPa) and 5-HT (PPa and PSPa). Dorso-ventral subdivisions were only evidenced in the SPa (SPaD, SPaV; respectively) by means of Pax6 andScNkx2.8(respectively). Interestingly,ScNkx2.8expression overlaps over the alar-basal boundary, asNkx2.2does in other vertebrates. Our results reveal evidences for the existence of different groups of tangentially migrated cells expressingScOtp,Pax6, andScDlx2. The genoarchitectonic comparative analysis suggests alternative interpretations of the rostral-most alar plate in prosomeric terms and reveals a conserved molecular background for the vertebrate alar hypothalamus likely acquired before/during the agnathan-gnathostome transition, on whichOtp,Pax6,Lhx5, andNeurog2are expressed in the Pa whileDlxandNkx2.2/Nkx2.8 are expressed in the SPa.
authors.affiliation: Grupo BRAINSHARK, Departamento de Biología Funcional, Universidade de Santiago de Compostela Santiago de Compostela, Spain.
authors.forename: Gabriel N
authors.initials: GN
authors.lastname: Santos-Durán
authors.affiliation: Grupo BRAINSHARK, Departamento de Biología Funcional, Universidade de Santiago de Compostela Santiago de Compostela, Spain.
authors.forename: Susana
authors.initials: S
authors.lastname: Ferreiro-Galve
authors.affiliation: CNRS, UMR 7355, University of Orleans Orleans, France.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Menuet
authors.affiliation: Grupo BRAINSHARK, Departamento de Biología Funcional, Universidade de Santiago de CompostelaSantiago de Compostela, Spain; Centre for Integrative Physiology, University of EdinburghEdinburgh, UK.
authors.forename: Idoia
authors.initials: I
authors.lastname: Quintana-Urzainqui
authors.affiliation: Sorbonne Universités, UPMC, CNRS UMR7232 Biologie Intégrative des Organismes Marins, Observatoire Océanologique Banyuls sur Mer, France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Mazan
authors.affiliation: Grupo BRAINSHARK, Departamento de Biología Funcional, Universidade de Santiago de Compostela Santiago de Compostela, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Rodríguez-Moldes
authors.affiliation: Grupo BRAINSHARK, Departamento de Biología Funcional, Universidade de Santiago de Compostela Santiago de Compostela, Spain.
authors.forename: Eva
authors.initials: E
authors.lastname: Candal
keywords: Dlx; Otp; Pax6; alar/basal boundary; chondrichthyan; development; evolution; forebrain