Neural - Myelencephalon Development

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Introduction

Stage10 sem6.jpg

Neural development is one of the earliest systems to begin and the last to be completed after birth. This development generates the most complex structure within the embryo and the long time period of development means in utero insult during pregnancy may have consequences to development of the nervous system.

The early central nervous system begins as a simple neural plate that folds to form a groove then tube, open initially at each end. Failure of these opening to close contributes a major class of neural abnormalities (neural tube defects).

Within the neural tube stem cells generate the 2 major classes of cells that make the majority of the nervous system : neurons and glia. Both these classes of cells differentiate into many different types generated with highly specialized functions and shapes. This section covers the establishment of neural populations, the inductive influences of surrounding tissues and the sequential generation of neurons establishing the layered structure seen in the brain and spinal cord.

  • Neural development beginnings quite early, therefore also look at notes covering Week 3- neural tube and Week 4-early nervous system.
  • Development of the neural crest and sensory systems (hearing/vision/smell) are only introduced in these notes and are covered in other notes sections.


Neural Links: neural | ventricular | ectoderm | Stage 22 | gliogenesis | neural fetal | Medicine Lecture - Neural | Lecture - Ectoderm | Lecture - Neural Crest | Lab - Early Neural | neural crest | Sensory | neural abnormalities | folic acid | iodine deficiency | Fetal Alcohol Syndrome | Postnatal | Postnatal - Neural Examination | Histology | Historic Neural | Category:Neural
Neural Parts: neural | prosencephalon | telencephalon cerebrum | amygdala | hippocampus | basal ganglia | lateral ventricles | diencephalon | Epithalamus | thalamus | hypothalamus‎ | pituitary | pineal | third ventricle | mesencephalon | tectum | cerebral aqueduct | rhombencephalon | metencephalon | pons | cerebellum | myelencephalon | medulla oblongata | spinal cord | neural vascular | meninges | Category:Neural

Some Recent Findings

  • Isthmus organizer for mesencephalon and metencephalon[1] " Brain vesicles formation is the first sign of regionalization. Classical transplantation using quail and chick embryos revealed that the mesencephalon-metencephalon boundary (isthmus) functions as an organizer of the mesencephalon and metencephalon. Fgf8 is accepted as a main organizing molecule of the isthmus. Strong Fgf8 signal activates the Ras-ERK signaling pathway to differentiate the cerebellum. In this review, the historical background of the means of identifying the isthmus organizer and the molecular mechanisms of signal transduction for tectum and cerebellum differentiation is reviewed."
  • Role of Lmx1b and Wnt1 in mesencephalon and metencephalon development[2] "The isthmus is the organizing center for the tectum and cerebellum. Fgf8 and Wnt1 are secreted molecules expressed around the isthmus. The function of Fgf8 has been well analyzed, and now accepted as the most important organizing signal. Involvement of Wnt1 in the isthmic organizing activity was suggested by analysis of Wnt1 knockout mice. But its role in isthmic organizing activity is still obscure. Recently, it has been shown that Lmx1b is expressed in the isthmic region and that it may occupy higher hierarchical position in the gene expression cascade in the isthmus. We have carried out misexpression experiment of Lmx1b and Wnt1, and considered their role in the isthmic organizing activity. Lmx1b or Wnt1 misexpression caused expansion of the tectum and cerebellum. Fgf8 was repressed in a cells that misexpress Lmx1b, but Fgf8 expression was induced around Lmx1b-misexpressing cells. As Lmx1b induced Wnt1 and Wnt1 induced Fgf8 expression in turn, Wnt1 may be involved in non cell-autonomous induction of Fgf8 expression by Lmx1b. Wnt1 could not induce Lmx1b expression so that Lmx1b may be put at the higher hierarchical position than Wnt1 in gene expression cascade in the isthmus. We have examined the relationship among isthmus related genes, and discuss the mechanism of the formation and maintenance of isthmic organizing activity."
  • Early mesencephalon/metencephalon patterning and development of the cerebellum[3] "Fate mapping studies in chick have shown that at early stages the cerebellum derives from cells in the mesencephalon and metencephalon (mes-met). Transplantation studies in chick have implicated the mes-met junction (isthmus) as a source of secreted factors that organize development of the entire mes-met, perhaps by stimulating proliferation and specifying positional values across the region. Fgf-8 has been implicated as a major factor involved in the isthmus organizing activity. Gene expression studies indicate that the anterior and posterior expression domains of the homeobox genes Otx-2 and Gbx-2, respectively, are the earliest indication of a division of the brain."

Development Overview

Neuralation begins at the trilaminar embryo with formation of the notochord and somites, both of which underly the ectoderm and do not contribute to the nervous system, but are involved with patterning its initial formation. The central portion of the ectoderm then forms the neural plate that folds to form the neural tube, that will eventually form the entire central nervous system.

Early developmental sequence: Epiblast - Ectoderm - Neural Plate - Neural groove and Neural Crest - Neural Tube and Neural Crest


Neural Tube Primary Vesicles Secondary Vesicles Adult Structures
week 3 week 4 week 5 adult
neural plate
neural groove
neural tube

Brain
Prosencephalon Telencephalon Rhinencephalon, Amygdala, Hippocampus, Cerebrum (Cortex), Hypothalamus, Pituitary | Basal Ganglia, lateral ventricles
Diencephalon Epithalamus, Thalamus, Subthalamus, Pineal, third ventricle
Mesencephalon Mesencephalon Tectum, Cerebral peduncle, Pretectum, cerebral aqueduct
Rhombencephalon Metencephalon Pons, Cerebellum
Myelencephalon Medulla Oblongata
Spinal Cord

Early Brain Vesicles

Primary Vesicles

CNS primary vesicles.jpg

Secondary Vesicles

CNS secondary vesicles.jpg

References

  1. Harukazu Nakamura, Tatsuya Sato, Asuka Suzuki-Hirano Isthmus organizer for mesencephalon and metencephalon. Dev. Growth Differ.: 2008, 50 Suppl 1;S113-8 PubMed 18494704
  2. Eiji Matsunaga, Tatsuya Katahira, Harukazu Nakamura Role of Lmx1b and Wnt1 in mesencephalon and metencephalon development. Development: 2002, 129(22);5269-77 PubMed 12399317
  3. M Wassef, A L Joyner Early mesencephalon/metencephalon patterning and development of the cerebellum. Perspect Dev Neurobiol: 1997, 5(1);3-16 PubMed 9509514

Reviews

Nicholas D E Greene, Andrew J Copp Development of the vertebrate central nervous system: formation of the neural tube. Prenat. Diagn.: 2009, 29(4);303-11 PubMed 19206138


Articles

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Cite this page: Hill, M.A. (2018, December 11) Embryology Neural - Myelencephalon Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Neural_-_Myelencephalon_Development

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© Dr Mark Hill 2018, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G