Mesenchyme

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Mesenchyme_table_infobox_0

MesenchymeMesenchyme_header_cell_0_0_0
DetailsMesenchyme_header_cell_0_1_0
Carnegie stageMesenchyme_header_cell_0_2_0 Mesenchyme_cell_0_2_1
PrecursorMesenchyme_header_cell_0_3_0 Primarily mesodermMesenchyme_cell_0_3_1
IdentifiersMesenchyme_header_cell_0_4_0
TEMesenchyme_header_cell_0_5_0 Mesenchyme_cell_0_5_1

Mesenchyme (/ˈmɛsənkaɪm ˈmiːzən-/) is a type of connective tissue found mostly during the embryonic development of bilateral triploblast animals. Mesenchyme_sentence_0

Vertebrates Mesenchyme_section_0

Structure Mesenchyme_section_1

Mesenchyme is characterized morphologically by a prominent ground substance matrix containing a loose aggregate of reticular fibers and unspecialized mesenchymal stem cells. Mesenchyme_sentence_1

Mesenchymal cells can migrate easily, in contrast to epithelial cells, which lack mobility, are organized into closely adherent sheets, and are polarized in an apical-basal orientation. Mesenchyme_sentence_2

Development Mesenchyme_section_2

The mesenchyme originates from the mesoderm. Mesenchyme_sentence_3

From the mesoderm, the mesenchyme appears as an embryologically primitive "soup". Mesenchyme_sentence_4

This "soup" exists as a combination of the mesenchymal cells plus serous fluid plus the many different tissue proteins. Mesenchyme_sentence_5

Serous fluid is typically stocked with the many serous elements, such as sodium and chloride. Mesenchyme_sentence_6

The mesenchyme develops into the tissues of the lymphatic and circulatory systems, as well as the musculoskeletal system. Mesenchyme_sentence_7

This latter system is characterized as connective tissues throughout the body, such as bone, muscle and cartilage. Mesenchyme_sentence_8

A malignant cancer of mesenchymal cells is a type of sarcoma. Mesenchyme_sentence_9

Epithelial to mesenchymal transition Mesenchyme_section_3

Main article: Epithelial–mesenchymal transition Mesenchyme_sentence_10

The first emergence of mesenchyme occurs during gastrulation from the epithelial–mesenchymal transition (EMT) process. Mesenchyme_sentence_11

This transition occurs through the loss of epithelial cadherin, tight junctions, and adherens junctions on the cell membranes of epithelial cells. Mesenchyme_sentence_12

The surface molecules undergo endocytosis and the microtubule cytoskeleton loses shape, enabling mesenchyme to migrate along the extracellular matrix (ECM). Mesenchyme_sentence_13

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. Mesenchyme_sentence_14

Embryological mesenchymal cells expresses fibroblast-specific protein (Fsp1), which is indicative of their shared properties with the migratory adult fibroblasts, and c-Fos, an oncogene associated with the down-regulation of epithelial cadherin. Mesenchyme_sentence_15

Both formation of the primitive streak and mesenchymal tissue is dependent on the Wnt/β-catenin pathway. Mesenchyme_sentence_16

Specific markers of mesenchymal tissue include the additional expression of ECM factors such as fibronectin and vitronectin. Mesenchyme_sentence_17

Implantation Mesenchyme_section_4

The first cells of the embryo to undergo EMT and form mesenchyme are the extra-embryonic cells of the trophectoderm. Mesenchyme_sentence_18

These migrate from the body of the blastocyst into the endometrial layer of the uterus in order to contribute to the formation of the anchored placenta. Mesenchyme_sentence_19

Primary mesenchyme Mesenchyme_section_5

Primary mesenchyme is the first embryonic mesenchymal tissue to emerge, and it is produced from EMT in epiblast cells. Mesenchyme_sentence_20

In the epiblast, it is induced by the primitive streak through Wnt signaling, and produces endoderm and mesoderm from a transitory tissue called mesendoderm during the process of gastrulation. Mesenchyme_sentence_21

The formation of primary mesenchyme depends on the expression of WNT3. Mesenchyme_sentence_22

Other deficiencies in signaling pathways, such as in Nodal (a TGF-beta protein), will lead to defective mesoderm formation. Mesenchyme_sentence_23

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. Mesenchyme_sentence_24

Mesodermal tissue will continue to differentiate and/or migrate throughout the embryo to ultimately form most connective tissue layers of the body. Mesenchyme_sentence_25

Neural mesenchyme Mesenchyme_section_6

Embryological mesenchyme is particularly transitory and soon differentiates after migration. Mesenchyme_sentence_26

Neural mesenchyme forms soon after primary mesenchyme formation. Mesenchyme_sentence_27

The interaction with ectoderm and somite-forming morphogenic factors cause some primary mesenchyme to form neural mesenchyme, or paraxial mesoderm, and contribute to somite formation. Mesenchyme_sentence_28

Neural mesenchyme soon undergoes a mesenchymal–epithelial transition under the influence of WNT6 produced by ectoderm to form somites. Mesenchyme_sentence_29

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. Mesenchyme_sentence_30

Neural crest cells (NCCs) form from neuroectoderm, instead of the primary mesenchyme, from morphogenic signals of the neural crest. Mesenchyme_sentence_31

The EMT occurs as a result of Wnt signaling, the influence of Sox genes and the loss of E-cadherin from the cell surface. Mesenchyme_sentence_32

NCCs additionally require the repression of N-cadherin, and neural cell adhesion molecule. Mesenchyme_sentence_33

NCCs ingress into the embryo from the epithelial neuroectodermal layer and migrate throughout the body in order form multiple peripheral nervous system (PNS) cells and melanocytes. Mesenchyme_sentence_34

Migration of NCCs is primarily induced by BMP signaling and its inhibitor, Noggin. Mesenchyme_sentence_35

Invertebrates Mesenchyme_section_7

In some invertebrates, e.g., Porifera, Cnidaria, Ctenophora and some triploblasts (the acoelomates), mesenchyme refers to a more-or-less solid but loosely organized tissue consisting of a gel matrix (the mesoglea) with various cellular and fibrous inclusions, located between the epidermis and the gastrodermis. Mesenchyme_sentence_36

In some cases, the mesoglea is noncellular. Mesenchyme_sentence_37

Mesenchyme_unordered_list_0

  • In sponges, the mesenchyme is called mesohyl.Mesenchyme_item_0_0
  • In diploblasts (Cnidaria and Ctenophora), the mesenchyme is fully ectodermally derived. This kind of mesenchyme is called ectomesodermal, and is not considered true mesoderm.Mesenchyme_item_0_1
  • In triploblastic acoelomates (such as flatworms), the term parenchyma is sometimes used for the middle (mesenchymal) layer, in which the dense layer includes tissues derived from both ectoderm, and entomesoderm (true mesoderm, derived from entoderm).Mesenchyme_item_0_2

When cellular material is sparse or densely packed, as in cnidarians, the mesenchyme may sometimes be called collenchyma, or parenchyma in flatworms. Mesenchyme_sentence_38

When no cellular material is present as in Hydrozoa), the layer is properly called mesoglea. Mesenchyme_sentence_39

In some colonial cnidarians, the mesenchyme is perforated by gastrovascular channels continuous among colony members. Mesenchyme_sentence_40

This entire matrix of common basal material is called coenenchyme. Mesenchyme_sentence_41


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Mesenchyme.