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. 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.
The ectoderm contributes to the human embryo:
- nervous system, both central (neural plate) and peripheral (neural crest).
- epidermis of the skin (surface ectoderm) and pigmented cells (neural crest).
- head regions that contribution sensory and endocrine structures (placodes).
- adrenal gland medullary cells (neural crest).
Some Recent Findings
Frog ectoderm gene co-expression network
- Notch signaling in the division of germ layers in bilaterian embryos "Bilaterian embryos are triploblastic organisms which develop three complete germ layers (ectoderm, mesoderm, and endoderm). While the ectoderm develops mainly from the animal hemisphere, there is diversity in the location from where the endoderm and the mesoderm arise in relation to the animal-vegetal axis, ranging from endoderm being specified between the ectoderm and mesoderm in echinoderms, and the mesoderm being specified between the ectoderm and the endoderm in vertebrates. A common feature is that part of the mesoderm segregates from an ancient bipotential endomesodermal domain. The process of segregation is noisy during the initial steps but it is gradually refined. In this review, we discuss the role of the Notch pathway in the establishment and refinement of boundaries between germ layers in bilaterians, with special focus on its interaction with the Wnt/β-catenin pathway."
- A molecular atlas of the developing ectoderm defines neural, neural crest, placode, and nonneural progenitor identity in vertebrates "During vertebrate neurulation, the embryonic ectoderm is patterned into lineage progenitors for neural plate, neural crest, placodes and epidermis. Here, we use Xenopus laevis embryos to analyze the spatial and temporal transcriptome of distinct ectodermal domains in the course of neurulation, during the establishment of cell lineages. In order to define the transcriptome of small groups of cells from a single germ layer and to retain spatial information, dorsal and ventral ectoderm was subdivided along the anterior-posterior and medial-lateral axes by microdissections. Principal component analysis on the transcriptomes of these ectoderm fragments primarily identifies embryonic axes and temporal dynamics. This provides a genetic code to define positional information of any ectoderm sample along the anterior-posterior and dorsal-ventral axes directly from its transcriptome. In parallel, we use nonnegative matrix factorization to predict enhanced gene expression maps onto early and mid-neurula embryos, and specific signatures for each ectoderm area. The clustering of spatial and temporal datasets allowed detection of multiple biologically relevant groups (e.g., Wnt signaling, neural crest development, sensory placode specification, ciliogenesis, germ layer specification). We provide an interactive network interface, EctoMap, for exploring synexpression relationships among genes expressed in the neurula, and suggest several strategies to use this comprehensive dataset to address questions in developmental biology as well as stem cell or cancer research."
- Meis transcription factor maintains the neurogenic ectoderm and regulates the anterior-posterior patterning in embryos of a sea urchin, Hemicentrotus pulcherrimus "Precise body axis formation is an essential step in the development of multicellular organisms, for most of which the molecular gradient and/or specifically biased localization of cell-fate determinants in eggs play important roles. In sea urchins, however, any biased proteins and mRNAs have not yet been identified in the egg except for vegetal cortex molecules, suggesting that sea urchin development is mostly regulated by uniformly distributed maternal molecules with contributions to axis formation that are not well characterized. Here, we describe that the maternal Meis transcription factor regulates anterior-posterior axis formation through maintenance of the most anterior territory in embryos of a sea urchin, Hemicentrotus pulcherrimus. Loss-of-function experiments revealed that Meis is intrinsically required for maintenance of the anterior neuroectoderm specifier foxQ2 after hatching and, consequently, the morphant lost anterior neuroectoderm characteristics. In addition, the expression patterns of univin and VEGF, the lateral ectoderm markers, and the mesenchyme-cell pattern shifted toward the anterior side in Meis morphants more than they did in control embryos, indicating that Meis contributes to the precise anteroposterior patterning by regulating the anterior neuroectodermal fate.
|More recent papers
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|These papers originally appeared in the Some Recent Findings table, but as that list grew in length have now been shuffled down to this collapsible table.
See also the Discussion Page for other references listed by year and References on this current page.
- A BMP regulatory network controls ectodermal cell fate decisions at the neural plate border. "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."
||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).
- 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
- 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
- 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.
- 2 parts
- midline neural plate
- lateral surface ectoderm
- sensory placodes
- epidermis of skin, hair, glands, anterior pituitary, teeth enamel
Stage 10 neural groove to tube
- 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
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
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.
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
- 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
- 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
- ↑ 1.0 1.1 Plouhinec JL, Medina-Ruiz S, Borday C, Bernard E, Vert JP, Eisen MB, Harland RM & Monsoro-Burq AH. (2017). A molecular atlas of the developing ectoderm defines neural, neural crest, placode, and nonneural progenitor identity in vertebrates. PLoS Biol. , 15, e2004045. PMID: 29049289 DOI.
- ↑ 2.0 2.1 Reichert S, Randall RA & Hill CS. (2013). A BMP regulatory network controls ectodermal cell fate decisions at the neural plate border. Development , 140, 4435-44. PMID: 24089471 DOI.
- ↑ Favarolo MB & López SL. (2018). Notch signaling in the division of germ layers in bilaterian embryos. Mech. Dev. , 154, 122-144. PMID: 29940277 DOI.
- ↑ Yaguchi J, Yamazaki A & Yaguchi S. (2018). Meis transcription factor maintains the neurogenic ectoderm and regulates the anterior-posterior patterning in embryos of a sea urchin, Hemicentrotus pulcherrimus. Dev. Biol. , 444, 1-8. PMID: 30266259 DOI.
- ↑ <pubmed>8005032</pubmed>
Search NLM Online Textbooks: "Ectoderm" : Developmental Biology | The Cell- A molecular Approach | Molecular Biology of the Cell
Kutejova E, Briscoe J & Kicheva A. (2009). Temporal dynamics of patterning by morphogen gradients. Curr. Opin. Genet. Dev. , 19, 315-22. PMID: 19596567 DOI.
Charron F & Tessier-Lavigne M. (2007). The Hedgehog, TGF-beta/BMP and Wnt families of morphogens in axon guidance. Adv. Exp. Med. Biol. , 621, 116-33. PMID: 18269215 DOI.
Charron F & Tessier-Lavigne M. (2005). Novel brain wiring functions for classical morphogens: a role as graded positional cues in axon guidance. Development , 132, 2251-62. PMID: 15857918 DOI.
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