User:WH40kindogs/sandbox

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TBC addition to page of neurula concerning the different regions of the mesoderm within neurula stage embyros in vertebrate.

The mesoderm of the embyro in the neurula stage of a vertebrate can be divided into five regions. Ventral to the neural tube is the chordamesoderm. Lateral to either side of the neural tube is the paraxial mesoderm. The intermediate lateral region to the neural tube is the intermediate mesoderm. The fourth region is the lateral plate mesoderm. The last region is the head mesenchyme.

During the neurula stage of Xenopus laevis development the genes Xwnt-3 and Xwnt-4 are present. Within Xenopus neurulae firboblast growth factor 8 (FGF8a) induces the expression of Wnt8 transcripts to promote neural crest development. Pax transcription factors have a important role in early development, especially with regards to the CNS and neural crest. Pax3 and Pax7 are promoter both neural crest cell survival along with promoting environmental stress resistance. Pax3 blocks p53 function.

During early development Pax3 is expressed at the posterior and lateral area of the neural plate, the same region that the neural crest arises from. Neural crest defects were found to occur in mouse and human Pax3 mutants, indicating a importance of functionality. Within chicks, frogs and fish Pax3/Pax7 are activated by Wnt and FGF signaling.

Pax3 and Pax7 are required for neural crest induction after depletion of the two genes resulted in the lack of activation of the specific neural crest genes Snail2 and Foxd3, which didn't allow further development or emigration of neural crest. Signaling molecules such as Wnts, FGFs, and BMFs along with the transcription factors that include Msx, Snail, Sox8/9/10, and Pax3/7 genes play key roles in neural crest formation.

Using knockouts has been helpful for understanding the role and functions of several genes found in the neurula. For example, Wnt-1 was found to have no role in the closing of the neural plate, despite being present at the tip of the neural folds when it is closing. Though mutants of Wnt-1 does lead to pattern defects within the brain. Notch1 is involved with formation of somites. HNF-3 is needed for development of the notochord and node. Neurulation is a process in vertebrate embryos at the neurula stage that results in the formation of the neural tube, which is the result of the creation and folding of the neural plate upon itself. There are two types of neurulation, primary and secondary neurulation. In primary neurulation, which mainly occurs in amphibians and reptiles, refers to the process of how the neural plate folds inward to form the neural tube that will give rise to the brain and spinal cord. Secondary neurulation, mainly in fishes, occurs at the posterior section of the body where the neural tube if formed by the medullary cord forming into cavities that merge to form a single tube. Both primary and secondary neurulation occurs in birds and mammals with a few differences. In birds the neural tube closes anterior to posterior, while in mammals the middle is first closed followed by both ends closing.