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I've been thinking about the development of an embryo from the zygote stage.

How is it that when cytokinesis takes place at that stage, the cells all stick together in a little ball, but later in life, some are not bound to others (red blood cells, sperm cells, etc.)?

In other words, how is it that some cells are stuck together and some are separated? How does this property develop?

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up vote 8 down vote accepted

Cell-cell adhesion is a well-regulated mechanism, cells don't just stick together randomly, this interaction is mediated by specific molecules on the cell surfaces. The responsible proteins for that are the Cell Adhesion Molecules (CAMs) like integrins, cadherins and selectins. Which of these CAMs are present on the surface of a cell determines if those cells will bind to each other or not.

Cells can change their ability to adhere to each other or the extracellular matrix by expressing or not expressing different kinds of these molecules.

You can find a lot more information about this topic in the cell-cell adhesion chapter of "Molecular Biology of the Cell", available on the NCBI homepage.

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