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Primitive knot

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Title: Primitive knot  
Author: World Heritage Encyclopedia
Language: English
Subject: Embryology, Endodermic evagination, Gubernaculum testis, Basal plate (placenta), Axial mesoderm
Collection: Developmental Biology
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Primitive knot

Primitive knot
Details
Latin nodus primitivus
Days 17
Dorlands
/Elsevier
k_04/12471954
Anatomical terminology

The primitive knot (or primitive node) is the organizer for gastrulation in vertebrates.

Contents

  • Diversity 1
  • Development 2
  • Default model 3
  • References 4
  • External links 5

Diversity

  • In birds, it is known as "Hensen's node", and is named after its discoverer Victor Hensen.
  • In ) [1]

Development

In chick development, the primitive knot starts as a regional knot of cells that forms on the blastodisc immediately anterior to where the outer layer of cells will begin to migrate inwards - an area known as the primitive streak, which is involved with Koller's sickle. Posterior to the node is the primitive pit, where the cells of the epiblast (the upper layer of embryonic cells) initially begin to invaginate. This invagination expands posteriorly into the primitive groove as the cells layers continue to move into the space between the embryonic cells and the yolk. This differentiates the embryo into the three germ layers - endoderm, mesoderm, and ectoderm. The primitive knot migrates posteriorly as gastrulation proceeds, eventually being absorbed into the tail bud.

Default model

The cells of the primitive node secrete many cellular signals essential for neural differentiation. After gastrulation the developing embryo is divided into ectoderm, mesoderm, and endoderm. The ectoderm gives rise to epithelial and neural tissue, with neural tissue being the default cell fate. Bone morphogenetic proteins (BMPs) suppress neural differentiation and promote epithelial growth. Therefore, the primitive node (the dorsal lip of the blastopore) secretes BMP antagonists, including noggin, chordin, and follistatin.

References

  1. ^ Garcia-Fernàndez J, D'Aniello S, Escrivà H (2007). "Organizing chordates with an organizer". Bioessays 29 (7): 619–24.  

External links

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