Editing Morphogenesis (section)

===Cell-to-cell adhesion===
During embryonic development, cells are restricted to different layers due to differential affinities. One of the ways this can occur is when cells share the same cell-to-[[cell adhesion molecule]]s. For instance, homotypic cell adhesion can maintain boundaries between groups of cells that have different adhesion molecules. Furthermore, cells can sort based upon differences in adhesion between the cells, so even two populations of cells with different levels of the same adhesion molecule can sort out. In [[cell culture]] cells that have the strongest adhesion move to the center of a mixed aggregates of cells. Moreover, cell-cell adhesion is often modulated by cell contractility, which can exert forces on the cell-cell contacts so that two cell populations with equal levels of the same adhesion molecule can sort out. The molecules responsible for adhesion are called cell adhesion molecules (CAMs). Several types of cell adhesion molecules are known and one major class of these molecules are [[cadherin]]s. There are dozens of different cadherins that are expressed on different cell types. Cadherins bind to other cadherins in a like-to-like manner: [[E-cadherin]] (found on many epithelial cells) binds preferentially to other E-cadherin molecules. Mesenchymal cells usually express other cadherin types such as N-cadherin.<ref>{{cite journal |author1=Hulpiau, P. |author2=van Roy, F. |title=Molecular evolution of the cadherin superfamily |journal=Int. J. Biochem. Cell Biol. |volume=41 |issue=2 |pages=349–69 |date=February 2009 |pmid=18848899 |doi=10.1016/j.biocel.2008.09.027}}</ref><ref>{{cite journal |author1=Angst, B. |author2=Marcozzi, C. |author3=Magee, A. |title=The cadherin superfamily: diversity in form and function |journal=J Cell Sci |volume=114 |issue=Pt 4 |pages=629–41 |date=February 2001 |doi=10.1242/jcs.114.4.629 |pmid=11171368}}</ref>