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Definition of paraxial mesoderm | Meanning and Concept

Within the area of ​​medicine, the paraxial mesoderm is one of the three fragments of the middle germinative layer in the embryo . It is said to be enlarged, thick, with respect to the other mesoderm, and next to it is the intermediate mesoderm, which is followed by the lateral one. Its function is to produce the somites that will give structure to the skeleton and trunk muscles.


Paraxial mesoderm



Also, it is understood that the mesoderm is one of the three embryonic leaves or cellular mantles that form the embryo . Therefore, its formation can be carried out by enterocelia or schizocelia from a blastocyst in the process called gastrulation. In the process prior to the formation of the mesoderm and gastrulation, there are especially two layers, the hypoblast and the epiblast. The epithelial cells of the epiblast become mesenchymal cells with migrant capacity, invaginating and giving rise to the 3 embryonic layers, stimulating the epithelium of the hypoblast to the yolk sac.




It is important to mention that towards the beginning of the third week the paraxial mesoderm is constituted in fragments . These fragments, or somitomeras, arise in cephalic order to caudal. In the cephalic region the somitomeras are related to the neural plate constituting the neuromeres, giving rise to most of the cephalic mesenchyme. From the occipital region, the somitomeras are established in somites, which subsequently are unequal in 3 layers, in dermotome, sclerotome and myotome, which they will later create, the dermis of the skin, cartilage and bones and muscles respectively. 

The mesoderm comes out during the trilaminar period, which unfolds in the third week of gestation, when the end of the gastrulation process begins, the intraembryonic mesoderm on each side of the midline differentiates into a paraxial mesoderm, an intermediate and a lateral mesoderm. In this sense, the intraembryonic mesoderm strip located between the neural tube and the intermediate mesoderm. It provides a place for the somites that will integrate the skeleton and the trunk musculature. 

Now, the paraxial mesoderm seems to be developed by the Nogina signal, which blocks or antagonizes the work of BMP and is split into fragments called somitomersIt is said to be formed by spirals or concentric swirls of cells, which are compacted and concentrated through the formation of an epithelium and then isolated and form the somites. 

Therefore, the somites are responsible for the migratory routes of the cells of the neural crest and of the axons of the spinal nerves . The component that intervenes in the somite formation cycle is not well defined, one of the significant agents is the Notch signaling. This process shows, experimentally, that the boundary cells are marked with a proteinNotch or Lunatic fringe (regulated by the retreat of FGF8, which is produced by the cells of the primitive node). In the same way, the protein that activates Notch is electroporated in those cells; that is to say, the cells that delimit the limits of the somites are signalized and if cells with Notch are marked a new limit will be sealed. This shows the importance of this protein, because it controls the cascade of gene expression that finally separates tissues, such as the Hairy gene that collects a transcription element.
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Jack Evans

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