09.10.8 1 CHAPTER 13 PART-1, NEURAL CREST CELLS ZOO3603 Determination of cortical laminar identity in the ferret cerebrum Determination is made during the final cell division Older neuronal precursors migrate to farther. Depending on the “Birthday”, the final destination is determined Determination of cortical laminar identity in the ferret cerebrum After S phase committed During S phase conditional Depending on the cell cycle -- Foxg1 gene for layers 4 & 5. Transplant “early” neuronal precursors into “late” ventricular layer. Myelination in the central and peripheral nervous systems  Myelination --- part of axon is insulated at intervals by glial cells, oligodendrocyte.  Myelin sheath  Oligodendrocyte in central  Schwann cell in peripheral Ectodermal competence and the ability to respond to the optic vesicle inducer in Xenopus Only the head ectoderm is competent to respond to the signal from the optic vesicle by producing a lens. 09.10.8 2 Neural crest formation Major derivatives of the neural crest The neural crest differentiations 1. The neurons and glial cells of the sensory. sympathetic and parasympathetic nervous systems. 2. The epinephrine-producing cells of adrenal gland. 3. The pigment-containing cells of epidermis. 4. Many of the skeletal and connective tissue components of the head. The fate depends on the locations. Specification of the neural crest cells Schematic representation of neural crest formation in an amniote embryo Specified by moderate levels of BMPs, Wnts & FGFs inducing the neural plate specifiers Neural plate border specifiers, Distalless-5 & Pax3 inducing 2nd set, Slug and FoxD3.09.10.8 3 Schematic representation of neural crest formation in an amniote embryo Slug and FoxD3 are the neural crest specifiers. • FoxD3, essential for the specification of ectodermal cells. • Slug, required to leave the epitherium and nigration, Regions of the chick neural crest Four main regions of the crest.  Trunk neural crest  Cranial neural crest  Vagal and sacral neural crest  Cardiac neural crest • Migration pathways of trunk neural crest cells • The mechanisms of trunk neural crest migration • Emigration from the neural tube • The ventral migration pathway • The dorsal migration pathway Trunk neural Crest Trunk neural crest  Two migration pathway  Ventral pathway  Forming the dorsal root ganglia.  Middle portion becomes medulla of adrenal gland, secretes adrenaline (epinephrine)  Dorsal pathway  Becoming melanocytes, migrate into the ectoderm Neural crest cell migration in the trunk of the chick embryo Neural crest cell migration in the trunk of the chick embryo Ventral pathway  Neural crest cells are seen in the anterior of each sclerotome of somite, not in posterior one.  The prospective vertebral cartilage of the spine. Immuno-histo chemistry of HNK-1, a marker of neural crest cells 09.10.8 4 Neural crest cell migration in the trunk of the chick embryo Regional difference of migration Immuno-histo chemistry of HNK-1 Anterior Posterior Extensive migration No migration Dorsal pathway  Trunk cells that emigrate later travel along the dorsolateral pathway and become melanocytes, the meranin-forming pigment cells. Once in the ectoderm they colonize the skin and hair folicles. The mechanisms of trunk neural crest migration  What signals initiate it?  When does the migratory agent become competent?  How do the migratory agents know the route to travel?  What signals indicate that the destination has been reached? Questions on the migration Emigration from the neural tube All migrating neural crest cells are stained red by antibody to HNK-1 • Neural crest cell, HNK-1, Red • Cells leaving neural crest, RhoB, Green • Both, Yellow From neural plate, Wnt, BMP4 &7 From mesoderm, FGF Slug & RhoB protein induced RhoB establish the cytoskeletal conditions; Slug dissociate the E-cadheline. The ventral migration pathway Segmental restriction of neural crest cells and motor neurons by the ephrin proteins of the sclerotome Ephrin Neural crest cells , HNK-1 Anterior Anterior Posterior Posterior The ventral migration pathway Segmental restriction of neural crest cells and motor neurons by the ephrin proteins of the sclerotome Ephrin stripes The neural crest cells bind to the regions lacking ephrin in vitro. • Receptor for ephrin, Eph is on neural crest cells. • The cells will leave the ephrin-containing region. 09.10.8 5 Segmental restriction of neural crest cells and motor neurons by the ephrin proteins of the sclerotome The migration of spinal cord neural crest cells and motor neurones The dorsal migration pathway  The neural crest cells the migrate later follow the dorsal path to become melanocytes.  Ephrin stimulates the migration of late-migrating cells through the receptor, Eph.  Dermis secrete a chemotactic factore, stem cell factor (SCF). The dorsal migration pathway Hair follicle of a mouse The Pluri-potency of Neural Crest Cells Pluri-potency of trunk neural crest cells But, there is some restrictions on the differentiations. Pluripotency of trunk neural crest cells Only the cells of the cranial neural crest can become the cartilage and bone. 09.10.8 6 Differentiation of trunk neural crest cells Paracrine factors encountered in the environment help specify the different neural crest-derived lineages in the trunk Timing of the signals is critical. Ex.) Wnt Regional difference of neural crest cells are controlled by Hox genes. • Intra-membranous ossification • Tooth formation Cranial Neural Crest Cranial neural crest  Cranial neural crest  Entering the pharyngeal arch and forming the bones of the middle ear and jaw. Paleozoic Shark Alligator Human Migrational pathway from the cranial neural crest Rhombomere, compartment of hindbrain Pharyngeal arch Frontonasal process generates the facial skeleton Three major streams of the cranial crest cells in the migration  Midbrain & R1-2 to the 1st pharyngeal arch  Jawbones, bones of middle ear, trigeminal ganglion, ciliary muscle of the eye, facial skeleton  R4 to the 2nd pharyngeal arch  Hyoid cartilage of the neck, bones of middle ear, facial nerve  R6-8 to the 3rd and 4th pharyngeal arch  Hyoid cartilage, thymus, parathyroid, thyroid glands, clavicle Continued migration of