What Are Main Ectodermal Regions? • Three main parts of ectoderm – Epidermis and related structures – Neural tube derivatives: CNS brain and spinal chord, CNS – Neural crest Where Do Sense Organs Come From? • Parts from ectodermal thickenings or placodes • Olfactory – Nasal placode -> nasal sac -> nasal pit – Neurons connect to telencephalon • Auditory – Auditory placode induced by rhombencephalon -> auditory sac -> auditory vesicle – sinks beneath epidermis -> labyrinth of inner ear • Optic – Lens placode becomes lens How Does the Eye Form? • Roof archenteron induces optic vesicle • Forms optic cup which induces lens • Lens induces cornea • Neurons grow into brain through optic stalk SEM of Eye Formation Differentiation of Retinal Neurons Pigmented layer of retina neural layer of retina Multiple Inductions in Mouse Eye Development How Does Neural Crest Originate? Some Major Neural Crest Derivatives • Some neurons – Cranial – Sensory and sympathetic neurons • Schwann and glial cells (supportive) • Connective tissue of the head (cartilage and bone) • Pigment cells of dermis and epidermis Migration Paths of Neural Crest Cells • I – Dorsally between cord and epidermis iv • II – Laterally between cord and somites • III – Ventrally over and between somites • IV – Dorsally towards head Fates of Neural Crest Cells • I – Pigment cells of skin • II – Dorsal root ganglia (sensory neurons near neural tube) • III – Neurons that innervate organs (autonomic nervous system) – Adrenal medulla • IV – Pigment cells, sensory ganglia, autonomic nervous system as for trunk neural crest cells (above) – Facial connective tissue • Cartilage and bone in head – Parts of eyes, teeth, ears Potency of Neural Crest • Is neural crest – a mixed population of monopotent cells? – or uniform population of pluripotent cells? How Pluripotent is Neural Crest? • Label individual n.c. cell with fluorescent particles • Marked daughters make several cell types • So some are pluripotent cells Does Potency Become Restricted? • Others more restricted • Final determination by environmental factors.