Notochord

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Introduction

Human notochordal process and notochordal canal (Carnegie stage 8)

The notochord (axial mesoderm, notochordal process) is the defining structure forming in all chordate embryos (taxonomic rank: phylum Chordata). It is an early forming midline structure in the trilaminar embryo mesoderm layer initially ventral to the ectoderm, then neural plate and finally neural tube. This is a transient embryonic anatomy structure, not existing in the adult, required for patterning the surrounding tissues. The patterning signal secreted by notochord cells is sonic hedgehog (shh). This secreted protein binds to receptors on target cells activating a signaling pathway involved in that tissues differentiation and development. This response appears to be concentration dependent, that is the closer to the notochord the higher the shh concentration.


Thought to have at least 2 early roles in development and later roles in patterning surrounding tissues. 1. Mechanical, influencing the folding of the early embryo; 2. Morphogenic, secreting sonic hedgehog a protein which regulates the development of surrounding tissues (neural plate, somites, endoderm and other organs).


In humans, the notochord forms in week 3, is eventually lost from vertebral regions and contributes to the nucleus pulposus of the intervertebral disc during the formation of the vertebral column.


Links: Lecture - Week 3 | Sonic hedgehog | Week 3 | stage 7 | stage 8 | Epithelial Mesenchymal Transition | Notochord | Development Animation - Notochord | Neural | Axial Skeleton | Musculoskeletal | Gastrulation | Category:Notochord

Some Recent Findings

Notochord secreting sonic hedgehog (shown in white)
  • Mechanical control of notochord morphogenesis by extra-embryonic tissues in mouse embryos[1] "Here, we show that in mouse embryos, the expansion of the amniotic cavity (AC), which is formed between embryonic and extraembryonic tissues, provides the mechanical forces required for a type of morphogenetic movement of the notochord known as convergent extension (CE) in which the cells converge to the midline and the tissue elongates along the antero-posterior (AP) axis. The notochord is stretched along the AP axis, and the expansion of the AC is required for CE. Both mathematical modeling and physical simulation showed that a rectangular morphology of the early notochord caused the application of anisotropic force along the AP axis to the notochord through the isotropic expansion of the AC. AC expansion acts upstream of planar cell polarity (PCP) signaling, which regulates CE movement. Our results highlight the importance of extraembryonic tissues as a source of the forces that control the morphogenesis of embryos."
  • Transcriptional profiling of the nucleus pulposus: say yes to notochord[2]"This editorial addresses the debate concerning the origin of adult nucleus pulposus cells in the light of profiling studies by Minogue and colleagues. In their report of several marker genes that distinguish nucleus pulposus cells from other related cell types, the authors provide novel insights into the notochordal nature of the former. Together with recently published work, their work lends support to the view that all cells present within the nucleus pulposus are derived from the notochord. Hence, the choice of an animal model for disc research should be based on considerations other than the cell loss and replacement by non-notochordal cells."
  • Notochord-derived BMP antagonists inhibit endothelial cell generation and network formation[3] "Embryonic blood vessel formation is initially mediated through the sequential differentiation, migration, and assembly of endothelial cells (ECs). ...We have previously shown that the notochord is responsible for the generation and maintenance of the avascular midline and that BMP antagonists expressed by this embryonic tissue, including Noggin and Chordin, can mimic this inhibitory role. Here we report that the notochord suppresses the generation of ECs from the mesoderm both in vivo and in vitro."
More recent papers
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<pubmed limit=5>Notochord</pubmed>

Notochord Development

Stage8 sem1.jpg Human Embryo notochordal plate

A scanning electron micrograph (SEM) image of the human embryo (stage 8, day 15).

The notochordal plate is the initial early transient cellular structure and region lying above the primitive streak, that will later be converted into the notochord.

<html5media height="360" width="280">File:Notochord 02.mp4</html5media>

Click Here to play on mobile device

This animation shows the early development of the notochord occurring during week 3 of human development.

This is a dorsal view of the embryonic disc, caudal (tail and connecting stalk end) to the bottom and rostral (head end) to the top. The indentations show the location of the cloacal (bottom) and buccopharyngeal (top) membranes. The raised region in the middle of the embryonic disc is the primitive node (Hensen's node).

The right hand side of the gastrulating embryonic disc is removed to the midline to show the the position of the initial axial process (purple). As the animation plays the axial process extends rostrally from the primitive node towards the buccopharyngeal membrane, where it stops.

A cross-section view above the primitive node is shown in the second animation below.


Grey - epiblast forming ectoderm | Yellow - endoderm | Orange - mesderm | Purple - axial process


Links: MP4 version | Quicktime version | Notochord Movie

<html5media height="200" width="240">File:Notochord 01.mp4</html5media>

Click Here to play on mobile device


This animation shows the early development of the notochord in relation to the endoderm in the trilaminar embryo.

The view is a cross-section showing how the axial process initially is formed, then fused with the endoderm, to finally separate as a midline mesoderm structure.


Yellow - endoderm | Purple - axial process


Links: MP4 version | Notochord Movie

Patterning

Neuralplate cartoon.png Somite cartoon5.png
Neural tube patterning Somite patterning


Development

Week 4

Stage11 sem100.jpg

Human embryo 25 days, 19 somite pairs Scanning EM. (Carnegie stage 11)

Week 8

Stage22 vertebra and spinal cord 1.jpg

Vertebra and Spinal cord (Carnegie Stage 22)

Nucleus Pulposus

Gray0065.jpg

Ossification endochondral 1c.jpg

Mouse Notochord

Mouse (E11) Notochord labeling HNF3beta[4]
Mouse embryo E11 HNF3beta notochord marker 02.jpg Mouse embryo E11 HNF3beta notochord marker 03.jpg Mouse embryo E11 HNF3beta notochord marker 04.jpg
  • nc; notochord, fp; floor plate.
  • lb; lung bud, hg; hindgut, st; stomach.
  • HNF3beta - FORKHEAD BOX A2 (FOXA2) Hepatocyte nuclear factor 3β (HNF3β)


Links: Image 1 - E11 Notochord | Image 2 - E11 Notochord | Image 3 - E11 Notochord | Image 4 - E11 Notochord | Notochord | Mouse Development | Category:Mouse E11.0 | Image- Mouse embryo E11 and tomography | Image - Mouse embryo E11 tomography | OMIM FORKHEAD BOX A2

Molecular Factors

Xenopus FoxA4 model
Xenopus FoxA4 model[5]

Abnormalities

Abnormalities include remnants of notochord that fail to regress. Locations can be along the embryonic path of the notochord and include: ecchordosis physaliphora, odontoid process of the axis, and in the coccyx. Less common locations are in the nasopharynx (Tornwaldt's cysts).

Chordoma

Rare type of bone cancer arising from remnants of the embryonic notochord (for review see[6]) Nearly all chordomas express the T-box transcription factor brachyury.


Links: [Developmental Signals - Tbx|Tbx]] | chordoma foundation

Ecchordosis physaliphora

Benign ectopic nests found along the craniospinal axis forming from notochordal remnants.[7]

Tornwaldt's cysts

A rare nasopharyngeal lesion occurring in humans thought to develop from remnants of the embryonic notochord adjacent with the embryonic foregut.[8][9] These cysts are covered by the nasopharynx mucous membrane. Named after Gustav Ludwig Tornwaldt (1843 - 1910) a German physician, the name is also spelled Thornwaldt.


References

  1. <pubmed>24509350</pubmed>
  2. <pubmed>20497604</pubmed>
  3. <pubmed>19041859</pubmed>
  4. <pubmed>22132119</pubmed>| PLoS One.
  5. <pubmed>25343614</pubmed>| PLoS ONE
  6. <pubmed>26363792</pubmed>
  7. <pubmed>27158576</pubmed>
  8. <pubmed>7856446</pubmed>
  9. <pubmed>17315835</pubmed>

Reviews

<pubmed></pubmed> <pubmed>21967331</pubmed> <pubmed>20568241</pubmed> <pubmed>15890825</pubmed>| Development

Articles

<pubmed>24509350</pubmed> <pubmed>20565707</pubmed> <pubmed>20041163</pubmed> <pubmed>19997509</pubmed> <pubmed>18629866</pubmed>

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


Search Pubmed: Notochord

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Cite this page: Hill, M.A. (2024, March 29) Embryology Notochord. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Notochord

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G