Gastrulation - in Amniotes - Formation of The Primitive Streak

Formation of The Primitive Streak

The primitive streak is formed at the beginning of gastrulation and is found at the junction between the extraembryonic tissue and the epiblast on the posterior side of the embryo and the site of ingression. Formation of the primitive streak is reliant upon nodal signaling within the cells contributing to the primitive streak and BMP4 signaling from the extraembryonic tissue. Furthermore, Cer1 and Lefty1 restrict the primitive streak to the appropriate location by antagonizing nodal signaling. The region defined as the primitive streak continues to grow towards the distal tip.

During the early stages of development, the primitive streak is the structure that will establish bilateral symmetry, determine the site of gastrulation and initiate germ layer formation. To form the streak, reptiles, birds and mammals arrange mesenchymal cells along the prospective midline, establishing the first embryonic axis, as well as the place where cells will ingress and migrate during the process of gastrulation and germ layer formation. The primitive streak, extends through this midline and creates the antero-posterior body axis, becoming the first symmetry-breaking event in the embryo, and marks the beginning of gastrulation. This process involves the ingression of mesoderm and endoderm progenitors and their migration to their ultimate position, where they will differentiate into the three germ layers.

Read more about this topic:  Gastrulation, In Amniotes

Famous quotes containing the words formation of, streak, formation and/or primitive:

    ... the mass migrations now habitual in our nation are disastrous to the family and to the formation of individual character. It is impossible to create a stable society if something like a third of our people are constantly moving about. We cannot grow fine human beings, any more than we can grow fine trees, if they are constantly torn up by the roots and transplanted ...
    Agnes E. Meyer (1887–1970)

    No gray hairs streak my soul,
    no grandfatherly fondness there!
    I shake the world with the might of my voice,
    and walk—handsome,
    twentytwoyearold.
    Vladimir Mayakovsky (1893–1930)

    The formation of an oppositional world view is necessary for feminist struggle. This means that the world we have most intimately known, the world in which we feel “safe” ... must be radically changed. Perhaps it is the knowledge that everyone must change, not just those we label enemies or oppressors, that has so far served to check our revolutionary impulses.
    Bell (c. 1955)

    It was a very primitive kind of harbor, where boats were drawn up amid the stumps,—such a one, methought, as the Argo might have been launched in.
    Henry David Thoreau (1817–1862)