title: Nervous system development in cephalopods: How egg yolk-richness modifies the topology of the mediolateral patterning system.
abstract: Cephalopods possess the most complex centralized nervous system among molluscs and the molecular determinants of its development have only begun to be explored. To better understand how evolved their brain and body axes, we studied Sepia officinalis embryos and investigated the expression patterns of neural regionalization genes involved in the mediolateral patterning of the neuroectoderm in model species. SoxB1 expression reveals that the embryonic neuroectoderm is made of several distinct territories that constitute a large part of the animal pole disc. Concentric nkx2.1, pax6/gsx, and pax3/7/msx/pax2/5/8 positive domains subdivide this neuroectoderm. Looking from dorsal to ventral sides, the sequence of these expressions is reminiscent of the mediolateral subdivision in model species, which provides good evidence for "mediolateral patterning" conservation in cephalopods. A specific feature of cephalopod development, however, includes an unconventional orientation to this mediolateral sequence: median markers (like nkx2.1) are unexpectedly expressed at the periphery of the cuttlefish embryo and lateral markers (like Pax3/7) are expressed centrally. As the egg is rich with yolk, the lips of the blastopore (that classically organizes the neural midline) remain unclosed at the lateral side of the animal pole until late stages of organogenesis, therefore reversing the whole embryo topology. These findings confirm - by means of molecular tools - the location of both ventral and dorsal poles in cephalopod embryos.
authors.affiliation: Museum National d'Histoire Naturelle (MNHN), DMPA, UMR Biologie des Organismes et Ecosystèmes Aquatiques (BOREA), Sorbonne Universités, MNHN CNRS 7208, IRD 207, UPMC, 55 rue Buffon, CP51, 75005 Paris, France.
authors.forename: A
authors.initials: A
authors.lastname: Buresi
authors.affiliation: Museum National d'Histoire Naturelle (MNHN), DMPA, UMR Biologie des Organismes et Ecosystèmes Aquatiques (BOREA), Sorbonne Universités, MNHN CNRS 7208, IRD 207, UPMC, 55 rue Buffon, CP51, 75005 Paris, France.
authors.forename: A
authors.initials: A
authors.lastname: Andouche
authors.affiliation: Museum National d'Histoire Naturelle (MNHN), DMPA, UMR Biologie des Organismes et Ecosystèmes Aquatiques (BOREA), Sorbonne Universités, MNHN CNRS 7208, IRD 207, UPMC, 55 rue Buffon, CP51, 75005 Paris, France.
authors.forename: S
authors.initials: S
authors.lastname: Navet
authors.affiliation: Université Paris-Est Créteil, Paris, France.
authors.forename: Y
authors.initials: Y
authors.lastname: Bassaglia
authors.affiliation: Museum National d'Histoire Naturelle (MNHN), DMPA, UMR Biologie des Organismes et Ecosystèmes Aquatiques (BOREA), Sorbonne Universités, MNHN CNRS 7208, IRD 207, UPMC, 55 rue Buffon, CP51, 75005 Paris, France.
authors.forename: L
authors.initials: L
authors.lastname: Bonnaud-Ponticelli
authors.affiliation: Museum National d'Histoire Naturelle (MNHN), DMPA, UMR Biologie des Organismes et Ecosystèmes Aquatiques (BOREA), Sorbonne Universités, MNHN CNRS 7208, IRD 207, UPMC, 55 rue Buffon, CP51, 75005 Paris, France; Université Paris Sorbonne, Paris, France. Electronic address: baratte@mnhn.fr.
authors.forename: S
authors.initials: S
authors.lastname: Baratte
mesh_terms: D000818:Animals; D019521:Body Patterning; D004530:Egg Yolk / Q000502:physiology*; D004625:Embryo, Nonmammalian / Q000502:physiology* / Q000648:ultrastructure; D018507:Gene Expression Regulation, Developmental; D009420:Nervous System / Q000196:embryology*; D055495:Neurogenesis / Q000502:physiology*; D038081:Organogenesis; D010063:Ovum / Q000648:ultrastructure; D049833:Sepia / Q000196:embryology* / Q000235:genetics
keywords: Body plan organization; Cephalopods; Direct development; Mediolateral patterning; Neurogenesis; Sepia officinalis; Yolk-rich egg