Mesenchyme

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Mesenchymal
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Mesenchyme
H&E
Details
Carnegie stage6b
Precursorlateral mesoderm
Identifiers
TEE5.16.4.0.3.0.18
Anatomical terminology]

Mesenchyme (

undifferentiated cells that give rise to most tissues, such as skin, blood or bone.[2][3] The interactions between mesenchyme and epithelium help to form nearly every organ in the developing embryo.[4]

Vertebrates

Structure

Mesenchyme is characterized morphologically by a prominent

epithelial cells, which lack mobility, are organized into closely adherent sheets, and are polarized
in an apical-basal orientation).

Development

The mesenchyme originates from the mesoderm.[6] From the mesoderm, the mesenchyme appears as an embryologically primitive "soup". This "soup" exists as a combination of the mesenchymal cells plus serous fluid plus the many different tissue proteins. Serous fluid is typically stocked with the many serous elements, such as sodium and chloride. The mesenchyme develops into the tissues of the lymphatic and circulatory systems, as well as the musculoskeletal system. This latter system is characterized as connective tissues throughout the body, such as bone, and cartilage. A malignant cancer of mesenchymal cells is a type of sarcoma.[7][8]

Epithelial to mesenchymal transition

Main article: Epithelial–mesenchymal transition

The first emergence of mesenchyme occurs during gastrulation from the epithelial–mesenchymal transition (EMT) process. This transition occurs through the loss of epithelial cadherin, tight junctions, and adherens junctions on the cell membranes of epithelial cells.[9] The surface molecules undergo endocytosis and the microtubule cytoskeleton loses shape, enabling mesenchyme to migrate along the extracellular matrix (ECM). Epithelial–mesenchymal transition occurs in embryonic cells that require migration through or over tissue, and can be followed with a mesenchymal–epithelial transition to produce secondary epithelial tissues. Embryological mesenchymal cells express

c-Fos, an oncogene associated with the down-regulation of epithelial cadherin.[12][13] Both formation of the primitive streak and mesenchymal tissue is dependent on the Wnt/β-catenin pathway.[14] Specific markers of mesenchymal tissue include the additional expression of ECM factors such as fibronectin and vitronectin.[15]

Implantation

The first cells of the embryo to undergo EMT and form mesenchyme are the extra-embryonic cells of the

endometrial layer of the uterus in order to contribute to the formation of the anchored placenta.[16]

Primary mesenchyme

Primary mesenchyme is the first embryonic mesenchymal tissue to emerge, and it is produced from EMT in

Wnt signaling, and produces endoderm and mesoderm from a transitory tissue called mesendoderm during the process of gastrulation.[17]

The formation of primary mesenchyme depends on the expression of

Nodal (a TGF-beta protein), will lead to defective mesoderm formation.[9]

The tissue layers formed from the primitive streak invaginate together into the embryo and the induced

mesenchymal stem cells will ingress and form the mesoderm. Mesodermal tissue will continue to differentiate and/or migrate throughout the embryo to ultimately form most connective tissue layers of the body.[18]

Neural mesenchyme

Embryological mesenchyme is particularly transitory and soon differentiates after migration. Neural mesenchyme forms soon after primary mesenchyme formation.[19]

The interaction with

somites.[20] These structures will undergo a secondary EMT as the somite tissue migrates later in development to form structural connective tissue such as cartilage and skeletal muscle.[21]

BMP signaling and its inhibitor, Noggin.[22][23]

Invertebrates

In some

acoelomates), the term "mesenchyme" refers to a more-or-less solid but loosely organized tissue that consists of a gel matrix (the mesoglea) with various cellular and fibrous inclusions, located between the epidermis and the gastrodermis (non-triploblast animals usually are considered to lack "connective" tissue). In some cases, the mesoglea is noncellular.[24]

  • In sponges, the mesenchyme is called mesohyl.[25]
  • In diploblasts (Cnidaria and Ctenophora), the mesenchyme is fully ectodermally derived. This kind of mesenchyme is called ectomesodermal, and is not considered true mesoderm.
  • In triploblastic acoelomates (such as
    entoderm
    ).

When cellular material is sparse or densely packed, as in cnidarians, the mesenchyme may sometimes be called collenchyma, or parenchyma in flatworms.[25] When no cellular material is present as in Hydrozoa), the layer is properly called mesoglea.[25]

In some colonial cnidarians, the mesenchyme is perforated by gastrovascular channels continuous among colony members. This entire matrix of common basal material is called coenenchyme.[25]

References

  1. ^ "MESENCHYME English Definition and Meaning | Lexico.com". Archived from the original on September 29, 2019.
  2. ISBN 9780781790697
    .
  3. ^ "Definition of MESENCHYME". Merriam-Webster. Archived from the original on Feb 4, 2024.
  4. ^ MacCord, Kate (2012-09-14). "Mesenchyme". Embryo Project Encyclopedia. Arizona State University. Archived from the original on Jan 20, 2024.
  5. ^ Slomianka, Lutz. "Blue Histology - Connective Tissues". School of Anatomy and Human Biology - The University of Western Australia. Archived from the original on Mar 7, 2020.
  6. ISBN 9780323313353
    .
  7. ISBN 978-0-7817-8577-8
    .
  8. ISBN 978-0-7817-9485-5
    .
  9. ^
    PMID 19487818
    .
  10. ^ "S100A4 - Protein S100-A4 - Homo sapiens (Human)". UniProt. Archived from the original on Nov 21, 2021.
  11. PMID 21173249. Archived
    from the original on 30 Mar 2024 – via PubMed Central.
  12. PMID 9362334. Archived
    from the original on Mar 30, 2024.
  13. PMID 10629227
    .
  14. S2CID 39908122. Archived
    from the original on Feb 19, 2024 – via American Association for Anatomy - Wiley Online Library.
  15. S2CID 8435009. Archived from the original
    (PDF) on Jun 26, 2013.
  16. S2CID 33629601
    .
  17. S2CID 22368548
    .
  18. PMID 17046576
    .
  19. PMID 15196961
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  20. S2CID 32342256
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  21. S2CID 12161494
    .
  22. PMID 16043371
    .
  23. ISBN 9780878930975.{{cite book}}: CS1 maint: location missing publisher (link
    )
  24. ^
    ISBN 9780878930975.{{cite book}}: CS1 maint: location missing publisher (link
    )
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