Primitive Streak - Cellular Movements

Cellular Movements

The formation of the primitive streak involves the coordinated movement and re-arrangement of cells in the epiblast. Even before the streak is visible, epiblast cells have started to move. Two counter-rotating flows of cells meet at the posterior end, where the streak forms. There is little movement in the center of these flows, while the greatest movement is observed at the periphery of the vortices. The Polonaise Movement is key for the formation of the primitive streak. Cells overlaying Koller’s Sickle in the posterior end of the embryo move towards the midline, meet and change direction towards the center of the epiblast. Cells from the lateral posterior marginal zone replace those cells that left Koller’s Sickle by meeting at the center of this region, changing direction and extending anteriorly. As these cells move and concentrate at the posterior end of the embryo, the streak undergoes a single- to multi-layered epithelial sheet transition that makes it a macroscopically visible structure. Several mechanisms, including oriented cell division, cell-cell intercalation and chemotactic cell movement, have been proposed to explain the nature of the cellular movements required to form the primitive streak.

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Famous quotes containing the word movements:

    The movements of the eyes express the perpetual and unconscious courtesy of the parties.
    Henry David Thoreau (1817–1862)