Axis Formation Proteins

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Axis Formation Proteins

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Axis Formation Proteins Background

Origin of the Nieuwkoop Center

In determining how the medullary back lip gets its properties, the main clue comes from the experimental Peter New Science. He and his colleagues in the Netherlands demonstrated that the properties of this newly formed mesoderm are induced by the plant underneath them (speculative endoderm) cells. He removed the equatorial cells from the blastocyst and found that neither the animal cap (hypothetical ectoderm) nor the cap of the plant (the putative endoderm) produced mesodermal tissue. However, when the two caps are reconstituted, the animal cap cells are induced to form mesodermal structures such as the notochord, muscle, kidney cells and blood cells. The polarity of this induction (whether the animal cell is in the middle or the ventral mid-skin) depends on the dorsal-ventral polarity of the endoderm (plant) fragment. The ventral and lateral plant cells (cells closer to the entry side of the sperm) induce ventral (interstitial, blood) and intermediate (muscle, kidney) mesoderm, while the most dorsal plant cells specify the dorsal mesoderm component (torso, notochord) the attributes of the organizer. The backmost plant cell capable of inducing the blastocyst of the organelle is called the Nieuwkoop center.

Molecular biology of the Nieuwkoop Center

In Xenopus laevis, endoderm is capable of inducing mesoderm formation by causing putative mesoderm cells to express the Brachyury (Xbra) gene. The mechanism of this induction is not well understood (see Harland and Gerhart 1997), but the Xbra protein is a transcription factor that activates genes that produce mesodermal-specific proteins. Although all plant cells appear to be able to induce their upper marginal cells to become mesoderm, only the most plant cells on the back can indicate that the marginal cells on the upper edge become organizers. The main candidate for the factor that forms the Nieuwkoop center in these plant cells at the back is beta-catenin.

Summary of experiments by Nieuwkoop and by Nakamura and Takasaki (1970). (De Robertis, et al. 1992.) Figure 1. Summary of experiments by Nieuwkoop and by Nakamura and Takasaki (1970). (De Robertis, et al. 1992.)

Axial formation of organisms

1. Fish back-ventral axis formation

The embryonic shield of fish is essential for the formation of the dorsal-ventral axis of the embryo. If the embryonic shield of a primitive early embryo is transplanted to the ventral side of another contemporaneous embryo, it is transformed into the dosal mesoderm by inducing the lateral mesoderm and ventral mesoderm. At the same time, the embryonic shield develops the ectoderm into neural tissue instead of the epidermis, resulting in two hypocotyls. The embryo's embryonic shield is homologous to the amphibian's back lip, the organizer.

2. Fish front-rear axis formation

The formation of the anterior-posterior axis of the fish begins when the egg is produced, and the animal cap is a sign of the front end of the embryo. The formation of the anterior-posterior axis of the fish is regulated by two signal centers; the front-end developmental inducing factor is secreted by a small group of neurons located between the neuroectoderm and the surface ectoderm at the anterior end of the gut. Dorsal developmental inducing factor - produced by the precursor of the choroidal mesoderm of the marginal blastoderm

3. Bird back-ventral axis formation

The formation of the dorsal-ventral axis of birds begins in the cleavage stage and is the differentiation of the blastocyst stage. The back is formed on one side of the albumin (pH 9.5), and the abdomen is formed on one side of the lower blastoderm (pH 6.5).

4. Mammalian dorsal-ventral axis and anterior-posterior axis formation

On day 5.5 of mouse embryo development, a cluster of anterior visceral endoderm (AVE) cells specifically expressing the hex gene began to migrate from the distal end to the proximal end. The location of the AVE cell is the sign of the front end. The mammal determines the dorsal ventral surface based on the location of the cell mass within the embryo. The head and tail may be determined during ovulation, and it is not entirely clear how the mammals decide.

Reference:

  1. Axis Formation in Amphibians: The Phenomenon of the Organizer

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