Ectoderm

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Introduction

The trilaminar embryo

The top layer of the early trilaminar embryo germ layers (ectoderm, mesoderm and endoderm) formed by gastrulation. The ectoderm can be though of as having 4 early regions: neural plate, neural crest, surface ectoderm and placodes.

The ectoderm contributes to the human embryo:

  1. nervous system, both central (neural plate) and peripheral (neural crest).
  2. epidermis of the skin (surface ectoderm) and pigmented cells (neural crest).
  3. head regions that contribution sensory and endocrine structures (placodes).
  4. adrenal gland medullary cells (neural crest).


Ectoderm Links: Endoderm | Mesoderm | Ectoderm | Lecture - Ectoderm Development | Lecture - Neural Development | Lecture - Integumentary Development | Neural System Development | Neural Crest Development | Integumentary System Development | Placodes | Category:Ectoderm

Some Recent Findings

Zebrafish ectodermal patterning model[1]
  • A BMP regulatory network controls ectodermal cell fate decisions at the neural plate border.[1] "During ectodermal patterning the neural crest and preplacodal ectoderm are specified in adjacent domains at the neural plate border. BMP signalling is required for specification of both tissues, but how it is spatially and temporally regulated to achieve this is not understood. Here, using a transgenic zebrafish BMP reporter line in conjunction with double-fluorescent in situ hybridisation, we show that, at the beginning of neurulation, the ventral-to-dorsal gradient of BMP activity evolves into two distinct domains at the neural plate border: one coinciding with the neural crest and the other abutting the epidermis. In between is a region devoid of BMP activity, which is specified as the preplacodal ectoderm. We identify the ligands required for these domains of BMP activity. We show that the BMP-interacting protein Crossveinless 2 is expressed in the BMP activity domains and is under the control of BMP signalling. We establish that Crossveinless 2 functions at this time in a positive-feedback loop to locally enhance BMP activity, and show that it is required for neural crest fate. We further demonstrate that the Distal-less transcription factors Dlx3b and Dlx4b, which are expressed in the preplacodal ectoderm, are required for the expression of a cell-autonomous BMP inhibitor, Bambi-b, which can explain the specific absence of BMP activity in the preplacodal ectoderm. Taken together, our data define a BMP regulatory network that controls cell fate decisions at the neural plate border."
More recent papers  
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This table shows an automated computer PubMed search using the listed sub-heading term.

  • Therefore the list of references do not reflect any editorial selection of material based on content or relevance.
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References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability.

Links: References | Discussion Page | Pubmed Most Recent | Journal Searches


Search term: Ectoderm Development | Images

Ying Wang, Rohinton P Edalji, Sanjay C Panchal, Chaohong C Sun, Stevan W Djuric, Anil Vasudevan Are We There Yet? - Applying Thermodynamic and Kinetic Profiling on Embryonic Ectoderm Development (EED) Hit-to-Lead Program. J. Med. Chem.: 2017; PubMed 28926243

Varalee Yodsurang, Chizu Tanikawa, Takafumi Miyamoto, Paulisally Hau Yi Lo, Makoto Hirata, Koichi Matsuda Identification of a novel p53 target, COL17A1, that inhibits breast cancer cell migration and invasion. Oncotarget: 2017, 8(34);55790-55803 PubMed 28915553

Mao-Rong Zhu, Dao-Hai Du, Jun-Chi Hu, Lian-Chun Li, Jing-Qiu Liu, Hong Ding, Xiang-Qian Kong, Hua-Liang Jiang, Kai-Xian Chen, Cheng Luo Development of a high-throughput fluorescence polarization assay for the discovery of EZH2-EED interaction inhibitors. Acta Pharmacol. Sin.: 2017; PubMed 28858300

Wenhua Yu, Fang Zhang, Shiyan Wang, Yi Fu, Jiahuan Chen, Xiaodong Liang, Huangying Le, William T Pu, Bing Zhang Depletion of polycomb repressive complex 2 core component EED impairs fetal hematopoiesis. Cell Death Dis: 2017, 8(4);e2744 PubMed 28406475

Shanshan Ai, Yong Peng, Chen Li, Fei Gu, Xianhong Yu, Yanzhu Yue, Qing Ma, Jinghai Chen, Zhiqiang Lin, Pingzhu Zhou, Huafeng Xie, Terence W Prendiville, Wen Zheng, Yuli Liu, Stuart H Orkin, Da-Zhi Wang, Jia Yu, William T Pu, Aibin He EED orchestration of heart maturation through interaction with HDACs is H3K27me3-independent. Elife: 2017, 6; PubMed 28394251

This animation shows the embryonic disc from the amniotic cavity side ectoderm (human week 3) onward.
  • Neural plate (blue) in central region of the ectoderm.
  • Primitive streak extending from the bottom of the neural plate.
  • Epidermis primordia (white) region surrounding the neural plate. Integumentary (skin) development will be briefly covered here.
  • Buccopharnygeal and Cloacal membranes (circular region above and below the neural plate).


Stage10 neural sm.jpg Stage10 SEM1.jpg

Ectoderm Development

Stage10 neural sm.jpg
Stage10 SEM1.jpg

Introduction

Note that there are other pages describing neural (central nervous system; brain and spinal cord) and neural crest (peripheral nervous system; sensory and sympathetic ganglia). Epidermis (integumentary, skin contribution) development will be briefly mentioned due to its ectoderm origin.

Objectives

  • Understanding of events during the third and fourth week of development
  • Understanding the process of notochord formation
  • Understanding the process of early neural development
  • Brief understanding of neural crest formation
  • Brief understanding of epidermis formation
  • Understanding of the adult components derived from ectoderm
  • Brief understanding of early neural abnormalities

Textbook References

  • Human Embryology (3rd ed.) Chapter 5 p107-125
  • The Developing Human: Clinically Oriented Embryology (6th ed.)
  • Moore and Persaud Chapter 18 p451-489
  • Essentials of Human Embryology Larson Chapter 5 p69-79
  • Before We Are Born (5th ed.) Moore and Persaud Chapter 19 p423-458

Development Overview

Notochord

  • forms initially as the Axial Process, a hollow tube which extends from the primitive pit , cranially to the oral membrane
  • the axial process then allow transient communication between the amnion and the yolk sac through the neuroenteric canal.
  • the axial process then merges with the Endodermal layer to form the Notochordal Plate.
  • the notochordal plate then rises back into the Mesodermal layer as a solid column of cells which is the Notochord.

Ectoderm

  • 2 parts
  • midline neural plate
    • columnar
  • lateral surface ectoderm
    • cuboidal
    • sensory placodes
    • epidermis of skin, hair, glands, anterior pituitary, teeth enamel

Neural Plate

Neuralplate cartoon.png
Stage 10 neural groove to tube

Click Here to play on mobile device

Development of the neural plate region at the embryonic disc stage.

Dorsal view of the embryonic disc from the amniotic cavity side showing the ectoderm with the central region developing into the neural plate.

The neural plate extends from buccopharyngeal membrane to primitive node and forms above the notochord and paraxial mesoderm.The neuroectodermal cells form a broad brain plate and narrower spinal cord region.

Three specific regions medial to lateral can also be identified: midline region floor plate, neural plate, edge of neural plate neural crest

  • extends from buccopharyngeal membrane to primitive node
  • forms above notochord and paraxial mesoderm
  • neuroectodermal cells
    • broad brain plate
    • narrower spinal cord
  • 3 components form: floor plate, neural plate, neural crest

Neural Determination- neuronal populations are specified before plate folds

  • signals from notochord and mesoderm - secrete noggin, chordin,follistatin
    • all factors bind BMP-4 an inhibitor of neuralation
    • bone morphogenic protein acts through membrane receptor
  • lateral inhibition generates at spinal cord level 3 strips of cells
  • expression of delta inhibits nearby cells, which express notch receptor, from becoming neurons
  • Delta-Notch inetraction- generates Neural strips

Neural Groove

Click Here to play on mobile device

This animation of early neural development from week 3 onward shows the neural groove fusing to form the neural tube.

View - Dorsolateral of the whole early embryo and yolk sac. Cranial (head) to top and caudal (tail) to bottom. Yolk sac is shown to the left.

Beginning with the neural groove initially fusing at the level of the 4th somite to form the neural tube and closing in both directions to leave 2 openings or neuropores: a cranial neuropore (anterior neuropore) and a caudal neuropore (posterior neuropore).

The animation also shows as the embryo grows and folds it increases in size relative to the initial yolk sac. Note also the increasing number of somites over time.

  • forms in the midline of the neural plate (day 18-19)
  • either side of which are the neural folds which continues to deepen until about week 4
  • neural folds begins to fuse, beginning at 4th somite level

Neural Tube

Stage 12 caudal neuropore
  • the neural tube forms the brain and spinal cord
  • fusion of neural groove extends rostrally and caudally
  • begins at the level of 4th somite
  • closes neural groove "zips up" in some species.
    • humans appear to close at multiple points along the tube.
  • leaves 2 openings at either end - Neuropores
    • cranial neuropore closes before caudal

Failure for the neural tube to close correctly or completely results in a neural tube defect.

Secondary Neuralation

Click Here to play on mobile device

This animation shows the early developmental process often described as secondary neurulation.

Red - site of secondary neurulation | Blue - neural tube

  • caudal end of neural tube formed by secondary neuralation
  • develops from primitive streak region
  • solid cord canalized by extension of neural canal
  • mesodermal caudal eminence
Links: MP4 version | Neural System Development


Neural Crest

  • a population of cells at the edge of the neural plate that lie dorsally when the neural tube fuses
    • dorsal to the neural tube, as a pair of streaks
    • pluripotential, forms many different types of cells
    • cells migrate throughout the embryo
    • studied by quail-chick chimeras
    • transplanted quail cells have obvious nucleoli compared with chicken

Neural Crest Derivitives

  • dorsal root ganglia
  • autonomic ganglia
  • adrenal medulla
  • drg sheath cells, glia
  • pia-arachnoid sheath
  • skin melanocytes
  • connective tissue of cardiac outflow
  • thyroid parafollicular cells
  • craniofacial skeleton
  • teeth odontoblasts
Links: Neural Crest Development

Ectodermal Placodes

  • Specialized ectodermal "patches" in the head region
  • Contribute sensory structures - otic placode (otocyst), nasal placode, lens placode
  • Contribute teeth

Human Neuralation - Early Stages

The stages below refer to specific Carneigie stages of development.

  • Carnegie stage 8 (about 18 postovulatory days) neural groove and folds are first seen
  • Carnegie stage 9 the three main divisions of the brain, which are not cerebral vesicles, can be distinguished while the neural groove is still completely open.
  • Carnegie stage 10 (two days later) neural folds begin to fuse near the junction between brain and spinal cord, when neural crest cells are arising mainly from the neural ectoderm
  • Carnegie stage 11 (about 24 days) the rostral (or cephalic) neuropore closes within a few hours; closure is bidirectional, it takes place from the dorsal and terminal lips and may occur in several areas simultaneously. The two lips, however, behave differently.
  • Carnegie stage 12 (about 26 days) The caudal neuropore takes a day to close.
    • the level of final closure is approximately at future somitic pair 31
    • corresponds to the level of sacral vertebra 2
  • Carnegie stage 13 (4 weeks) the neural tube is normally completely closed.

Secondary neurulation begins at stage 12 - is the differentiation of the caudal part of the neural tube from the caudal eminence (or end-bud) without the intermediate phase of a neural plate.

Above text modified from[2]

Movies

Neural Development
Neuralplate 001 icon.jpg
 ‎‎Neural Plate
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Neuraltube 001 icon.jpg
 ‎‎Neural Tube
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Secondary neurulation 01 icon.jpg
 ‎‎Secondary Neurulation
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Stage13-CNS-icon.jpg
 ‎‎Stage 13 Neural
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Stage13 MRI 3D02 icon.jpg
 ‎‎Embryo CNS
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Mouse neural tube 01 movie icon.jpg
 ‎‎Neural Tube Close
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Stage16 MRI 3D02 icon.jpg
 ‎‎Embryo CNS
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Stage16 MRI S01 icon.jpg
 ‎‎Embryo Stage 16
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Human embryo tomography Carnegie stage 17.jpg
 ‎‎Stage 17 Embryo
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Stage22-CNS-icon.jpg
 ‎‎Stage 22 Neural
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Stage23 MRI 3D02 icon.jpg
 ‎‎Embryo CNS
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Stage23 MRI S01 icon.jpg
 ‎‎Sagittal Head
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Abnormalities Ultrasound
Brain fissure development 03.jpg
 ‎‎Sylvian Fissure
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Adult human brain tomography.jpg
 ‎‎Adult Brain
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US Dandy-Walker 01.jpg
 ‎‎Dandy-Walker
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US Spina bifida GA19week.jpg
 ‎‎Spina Bifida
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Fetal-Brain-icon.jpg
 ‎‎Neural
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References

  1. 1.0 1.1 Sabine Reichert, Rebecca A Randall, Caroline S Hill A BMP regulatory network controls ectodermal cell fate decisions at the neural plate border. Development: 2013, 140(21);4435-44 PubMed 24089471 | Development
  2. R O'Rahilly, F Müller Neurulation in the normal human embryo. Ciba Found. Symp.: 1994, 181;70-82; discussion 82-9 PubMed 8005032

Textbooks

Online Textbooks

Search

Search NLM Online Textbooks: "Ectoderm" : Developmental Biology | The Cell- A molecular Approach | Molecular Biology of the Cell

Reviews

Eva Kutejova, James Briscoe, Anna Kicheva Temporal dynamics of patterning by morphogen gradients. Curr. Opin. Genet. Dev.: 2009, 19(4);315-22 PubMed 19596567

Frédéric Charron, Marc Tessier-Lavigne The Hedgehog, TGF-beta/BMP and Wnt families of morphogens in axon guidance. Adv. Exp. Med. Biol.: 2007, 621;116-33 PubMed 18269215

Frédéric Charron, Marc Tessier-Lavigne Novel brain wiring functions for classical morphogens: a role as graded positional cues in axon guidance. Development: 2005, 132(10);2251-62 PubMed 15857918


External Links

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Take the Quiz

1. Ectoderm refers only to the neural plate region of the trilaminar embryo

true
false
The entire layer of the trilaminar embryo is the ectoderm (meaning outer layer), the neural plate is only the central portion of this layer.

2. The central nervous system forms in the sequence:

norochord to neural plate to neural tube
neural tube to neural plate to neural groove
neural plate to neural groove to neural tube
neural plate to neural crest to neural zone
The sequence neural plate to neural groove to neural tube represents the gradual folding of a flat surface sheet of ectodermal cells into a closed tube isolated from the embryo surface. The notochord is part of the mesoderm and regulates the initial overlying differentiation process. The neural crest are a population at the edge of the neural plate that do not get incorporated into the neural tube. I think I made up neural zone.

3. The neural plate is narrower at the caudal (tail) end and therefore closes earlier than the broad cranial (head) end.

true
false
The caudal or posterior neuropore closes after the cranial or anterior neuropore.

4. The correct sequence from cranial to caudal of the secondary brain vesicles is:

prosencephalon, mesencephalon, metencephalon, myelencephalon, rhombencephalon
telencephalon, diencephalon, metencephalon, mesencephalon, myelencephalon
telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon
prosencephalon, diencephalon, mesencephalon, myelencephalon, metencephalon
The prosencephalon and rhombencephalon are primary brain vesicles. The others are distractors using your lack of understanding of what the terms mean.

Your score is 0 / 0

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Cite this page: Hill, M.A. 2017 Embryology Ectoderm. Retrieved November 18, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/Ectoderm

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© Dr Mark Hill 2017, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G