Unit 16 Neurulation The neurula stage Formation of a dorsal hollow nerve cord neural tube a diagnostic feature of chordates Formation of the notochord and somites mesodermal structures that are diagnostic features of chordates Formation of the neural crest crucial for many cell types in vertebrates The post neurula is the phylotypic stage for vertebrates i e the stage that is diagnostic for a phylogenetic grouping of animals It includes formation of pharyngeal arches mesoderm and pharyngeal pouches endoderm Ernst Haeckel Ontogeny Recapitulates Phylogeny http en wikipedia org wiki File ErnstHaeckel jpg Phylotypic Stage The Myth Gilbert 3e Romanes s 1892 adaptation of a figure from Haeckel s Anthropogenie Karl Ernst von Baer Baer s Laws http en wikipedia org wiki File Karl Ernst von Baer 2 jpg Phylotypic Stage The Reality Wolpert et al 2e Fig 2 2 Neurulation Overview Browder et al 3e Fig 7 3 Amphibian Neurulation Overview Anterior Neural fold Neural plate Epidermis Posterior Amphibian Neurulation Overview Gilbert 10e Fig 10 3 Amphibian Neurulation Overview Gilbert 10e Fig 10 3 Amphibian Neurulation Overview Gilbert 10e Fig 10 3 Amphibian Neurulation Overview Gilbert 10e Fig 10 3 Amphibian Neurulation Overview Gilbert 10e Fig 10 3 Amphibian Neurulation Overview Gilbert 10e Fig 10 3 Amphibian Neurulation Overview Gilbert 10e Fig 10 3 Amphibian Neurulation Overview Gilbert 10e Fig 10 3 Amphibian Neurulation Overview Gilbert 10e Fig 10 3 Amphibians Notoplate Kalthoff 2e Fig 12 10 Amphibians Notoplate Kalthoff 2e Fig 12 14 Amphibian Neurulation PCP Required Normal Xenopus neurula Courtesy John Wallingford PCP disrupted Chick Neurulation courtesy Gary Schoenwolf Chick Neurulation Overview Gilbert 10e Fig 10 2 Chick Neurulation Overview Gilbert 10e Fig 10 2 Chick Neurulation Overview Gilbert 10e Fig 10 10 Chick Neurulation Overview Gilbert 10e Fig 10 10 Chick Neurulation Overview MHP medial hinge point Gilbert 10e Fig 10 4 Chick Neurulation Overview Gilbert 10e Fig 10 4 Chick Neurulation Overview DLHP dorsolateral hinge point Gilbert 10e Fig 10 4 Chick Neurulation Overview Gilbert 10e Fig 10 4 Chick Neurulation Overview Gilbert 10e Fig 10 4 Chick Neurulation Overview Gilbert 10e Fig 10 4 Neurulation Structures courtesy Kathy Tosney Chick Neurulation Timing Gilbert 10e Fig 10 10 Amphibians Cadherins E cadherin N cadherin Gilbert 4e Amphibians Perturbing Cadherins Gilbert 10e Fig 10 7 Mammalian Neurulation Gilbert 10e Fig 10 5 Mammalian Neurulation Gilbert 10e Fig 10 5 Mammalian Neurulation from A Child Is Born Mammalian Neurulation Looptail Strb E8 5 E8 5 Lp Lp craniorachischisis Doudney and Stanier 2005 Am J Med Gen Part C 135C 42 47 Human Neurulation Birth Defects Gilbert 7e Fig 12 5 Human Neurulation Spina Bifida Human Neurulation Anencephaly Gilbert 10e Fig 10 5 Neural tube Folate binding proteins folate binding protein 1 Fbp1 Gilbert 9e Fig 9 7 Brain Vesicles from A Child Is Born Neural derived eye structures come from forebrain Gilbert 10e Fig 10 10 Neural derived eye structures form from the forebrain Optic Lobes and Lens Formation Placodes are thickenings of surface epithelia The lens placode comes from epidermal ectoderm that is induced to form lens Gilbert 10e Fig 3 15 Optic Lobes and Lens Formation The lens forms as a hollow vesicle that later undergoes further differentiation to form lens fibers Gilbert 10e Fig 3 15 Optic Lobes and Lens Formation lens retina Gilbert 10e Fig 10 30 note reversed Retina cells require Rx genes to differentiate Retina cells require the homeobox gene Rx Gilbert 10e Fig 10 31 Retina cells require Rx genes to differentiate In humans mutations in Rx lead to anophthalmia Gilbert 9e Fig 9 33 Lens cells become highly differentiated Gilbert 10e Fig 10 35 Lens cells eject their nuclei and produce high levels of crystallins proteins that give lens cells their unique oprtical proterties Pax6 regulates crystallin gene expression Gilbert 10e Fig 10 35 Pax6 is a transcription factor expressed in the eye field that positively regulates crystallin gene expression Making eyeball stew ES cells can be cultured under conditions that favor eye differentiation Some cells will form optic cup like structures The Scientist March 2012 ES derived eye like structures express eye specific genes Rx gene expression Eiraku et al 2011 Nature 472 51 56 Vertebrates display metameric organization Metamerism repeating structures along an axis usually along the anterio posterior axis Rhombomeres Gilbert 10e Fig 10 11 Rhombomeres are segmentally repeated units in the vertebrate hindbrain Eph ephrin expression correlates with rhombomeres Eph receptors Ephrin ligands Rhombomeres show alternating expression of either Ephs or ephrins Lumsden A 1999 Nat Cell Bio 1 E83 E85 D V Specification Floor Plate Gilbert 10e Fig 10 14 D V Specification BMPs Shh Gilbert 10e Fig 10 13 D V Specification BMPs Shh Gilbert 10e Fig 10 13