It is worth reading this nice review article which deals with adherens junctions and also some other cell adhesion molecules.
Oda and Takeichi 2011 have this nice electron micrograph or cell-cell adhesion, but it is even more interesting to me that the area described with the confines of their arrows, and the area within their bracket, does not show as distinct an organization as the area inbetween their designated zones… Haha. see bottom two micrographs, their photo unretouched, and the area where I see amazing order, an area which is very organized.
semicircular arrangement (black lines), likely proteins which attach to whatever membrane proteins the circles are, and then the red lines as some molecule which links the former with some cytoskeletal element. There is a great microtubule over by their arrows, i don’t know what is under their bracket.
Just a note: it looks like the primitive junctional complexes in drosophila are the result of one-size-fits-all type molecule with little segments snipped out as DE-cadherin has every thing but the kitchen sink there….including laminin, proteolytic, and EGF-like domains.
It is overwhelming to move into a new field of study. In this case one borne out of looking at desmosomes. I am starting at the beginning with this overview for myself primarily, if someone else finds it useful, so much the better.
Cell adhesion molecules — a mind-blowing statement about how the cell has learned to interact with its environment over the last 3.9 billion years. It should not be surprising that a huge number (hundreds if not thousands) of molecules are out there in the cell membrane touching and feeling what is around…. either another cell, or matrix or the extracellular milieu. The adhesion molecules in desmosomes are part of this elaborate system to “group” “assemble” and become an “organism”… present in insects in highly organized and organized junctions. So here is a very basic summary of the Cell adhesion molecules.. a basic diagram without complete listings but helpful to me. There is a short list of some representatives of the four superfamilies on the left of the graph, no attempt made to be inclusive, but more to show diversity.
Think of the cell as a tiny tiny pincushion, the cell membrane packed with proteins which have an intracellular domain, an intracellular domain, and an extracellular portion, each little molecule protruding like an feeler into the environment — so to speak– to sense portions of, to signal to, to interact with, and/or adhere to. I marvel indeed.
A little acronmistic thing here…. of the four superfamilies of cell adhesion molecules it is kind of nice that two of them, the Cadherins (though i did find a report that says some cadherins lack a calcium binding domain…. maybe these are mutated..according to the author?) and the C-type lectins both are calcium dependent and begin with the letter C, while the other two begin with the letter I – and are calcium independent — that is Integrins and Immunoglobulins.
One other kind of cool thing is that two of the C-lectins, one in particular (that is surfactant protein A) can oligomerize into wonderful patterns seen electron microscopically, and the cadherins, desmoglein and desmocollin, appear to have a very organized extracellular and intracellular status as well.