M5 B ECTODERM - NEURULATION PDF

ECTODERM Neurulation ABI 3109 – Developmental Biology Department of Biological Sciences  Introduction: Organogenesis Ectoderm the epidermis of the skin, nervous system, sense organs and a few other cell types Endoderm  tissues that line the digestive tract and organs that develop as outgrowth...

ECTODERM Neurulation ABI 3109 – Developmental Biology Department of Biological Sciences  Introduction: Organogenesis Ectoderm the epidermis of the skin, nervous system, sense organs and a few other cell types Endoderm  tissues that line the digestive tract and organs that develop as outgrowths of the digestive tract (including the liver, pancreas, and lungs). Mesoderm  skeletal, muscle tissues and circulatory, excretory and reproductive systems.  Display full size Figure 1. A portrait of Hans Spemann and his assistant Hilde Pröscholdt Mangold.  Spemann-Mangold Organizer The Spemann-Mangold organizer, also known as the Spemann organizer, is a cluster of cells in the developing embryo of an amphibian that induces development of the central nervous system. Induction is the process by which the identity of certain cells influences the developmental fate of surrounding cells.  The Spemann-Mangold organizer experiment Display full size  Transplantation Experiment of Spemann and Mangold Has shown that the cells in the Dorsal Lip Blastophore have an extraordinary role in the formation of the dorsal mesoderm, particularly the notochord and some pharyngeal endoderm These cells have been referred to as the Spemann organizer since the cells here induces the formation of the CNS One important chemical that was later known to be the cause of the induction of the CNS is chordin (encoded by the gene chordin). Before the CNS is induced to form, chordin is a protein that dorsalizes early vertebrate embryonic tissues binds to bone morphogenetic proteins (BMPs) that may be involved also in organogenesis o the embryonic process by which the neural plate folds to give rise to the neural tube, which will form the central nervous system in vertebrates. Neurulation Primary neurulation  neural plate cells are directed to proliferate, invaginate and pinch off to form hollow tube Secondary neurulation  neural tube arises from solid cord of cells that sinks into the embryo  forms the spinal cord/medullary cord and mantle/intermediate zone  differentiates into neurons and glia Primary Neurulation formation of the shaping of the neural plate neural plate bending of the closure of the neural plate – neural groove – neural groove neural tube (neural fold) Primary Neurulation Formation and shaping of the neural plate  underlying dorsal mesoderm signals the ectodermal cells to elongate  shaping by intrinsic movement of epidermal and neural plate regions Primary Neurulation Bending of the Neural Plate  MHP – medial hinge point  DLHP – dorsolateral hinge points  becomes wedge shaped due to microfilaments & microtubules inhibited by colchicine & cytochalasin B Primary Neurulation Closure of Neural Tube  paired neural folds are brought together at the dorsal midline  formation of neuropore  neural tube separates from ectoderm by N- cadherin and N-CAM  Genetics: Pax3, Sonic hedgehog (Shh), open brain (opb)  Dietary: folic acid (Vit B12) and cholesterol Differentiation of Neural Tube neural tube & its lumen bulge & constrict to form the brain and spinal cord chambers cell population on neural tube rearrange to form different regions of CNS neuroepithelial cells differentiates into neurons and glial cells Neurulation of Humans Neurulation in Humans Neurulation in Humans Neurulation in Humans Neurulation in Humans Neurulation in Humans Neurulation in Humans Neurulation in Humans Neurulation in Humans Differentiation of Neural Tube: Cranial- Vesiculation Differentiation of Neural Tube telencephalon prosencephalon diencephalon mesencephalon mesencephalon rhombencephalon metencephalon myelencephalon  Derivatives of the Three Primary Vesicles Primary Vesicles Secondary Vesicles Neural Derivatives Cavity Derivatives Cerebral Telencephalon hemispheres and Lateral ventricle globus pallidus Prosencephalon Thalamus, Diencephalon hypothalamus, and Third Ventricle epithalamus Mesencephalon Mesencephalon Midbrain Cerebral aqueduct Pons and Upper part of Metencephalon cerebellum 4th ventricle Rhombencephalon Lower part of Myelencephalon Medulla 4th ventricle/central canal  Neurogenesis Neural stem cell/ neuroderm cells begin to differentiate into neurons and glial cells. Neurons migrate throughout the brain, and once they have reached their final destination they develop axons and dendrites, forming synapses. Neuronal Formation > 1011 neurons & 1012 glial cells CNS: oligodendrocyte PNS: Schwann cell  Spinal cord the caudal end develops to form the spinal cord Cells on the dorsal side form the alar plate, which subsequently becomes the dorsal horn (posterior) Cells at the ventral end form the basal plate, which then becomes the ventral horn (anterior) Neural Tube Defects failure of the neural tube to close  anencephaly, spinabifida, craniorachischisis  Anencephaly failure of the neural tube to close at the cranial/cephalic end, leading to the partial absence of the brain and skull lethal condition, and newborns with this congenital abnormality typically do not survive longer than a few hours or days after birth  Spina Bifida results from incomplete closure of the neural tube at the caudal end (most commonly in the lumbar region). There are three main types of spina bifida, of increasing severity: Oculta, Meningocele, Myelomeningocele Spina bifida occulta mildest and most common type. This type of spina bifida results in a small separation or gap in one or more of the bones of the spine an incomplete closure of the vertebrae, without protrusion of the spinal cord. Most people with this form of spina bifida are unaware of having it, and its discovery is often incidental Meningocele (meningeal cyst) a sac of fluid comes through an opening in your baby's back, but their spinal cord isn't in the sac. There's usually little or no nerve damage. the meninges protrude between the vertebrae posteriorly, but the spinal cord is undamaged. simplest form of open neural tube defects characterized by cystic dilatation of meninges containing cerebrospinal fluid without any neural tissue. Myelomeningocele(open spina bifida most serious type spinal canal is open along several vertebrae in the lower or middle back Part of the spinal cord, including the spinal cord's protective covering and spinal nerves, push through this opening at birth, forming a sac on the baby's back. Tissues and nerves usually are exposed baby prone to dangerous infections and may cause loss of movement in the legs, and bladder and bowel dysfunction Other ECTODERMAL DERIVATIVES Outer Ectoderm  cells covering the embryo after neurulation  form the periderm that is shed off and basal layer (germinativum) – give rise to spinous layer Outer/Surface Ectoderm  Outer/Surface Ectoderm olfactory epithelium, mouth epithelium, tooth enamel, adenohypophysis, lens, cornea, cochlear duct, semicircular ducts Neural Crest originates from cells located along the margins of neural plate break free from neural tube and lose cell to cell adhesiveness cranial, circumpahryngeal and trunk neural crest  Neural Crest  Endocrine and paraendocrine derivatives  PNS  adrenal medulla  dermal smooth muscles Neural Crest  Pigment cells  Anterior facial cartilage  Connective tissue  Corneal endothelium  Tooth papillae  Adipose tissue  Connective tissue of salivary, lacrimal, thymus, thyroid and pituitary