Your "ready-mix patch"

I will praise thee; for I am fearfully and wonderfully made: marvellous are thy works; and that my soul knoweth right well. Psalm 139:14

"You’ve probably used those packets with two compartments that do something when the dividing membrane is broken, allowing the

components to mix: instant heat, instant cold, instant glue, or instant light.
Your body has something like that to repair its tissues. Tissues are the webs of specialized cells that distinguish us multicellular organisms from the rest, and the bulk of tissues are composed of epithelium.
Epithelial cells line up in tightly-knit ranks forming the lining of most organs, the lungs and windpipe, the digestive tract, and the skin. Because they are subject to injury, these membranes must have a means of repairing themselves quickly. So they have a kind of ready-mix patch that works only when two components combine. But the system must work flawlessly, or a disaster can result.

Keith Mostov and Mirjam Zegers talk about this in the Mar. 20 issue of Nature, “Cell Biology: Just Mix and Patch,” reporting on work by Paola Vermeer and company in the same issue. Epithelial cells have two linings.
Consider the respiratory tract as an example.
*One lining, the apical side, faces the airway.
*The other, the basolateral side, lines the other end and the

neighboring cells.
These two linings are segregated by a kind of O-ring seal that makes a tight fit between neighboring cells.
Scientists recently found that the basolateral membrane has one component of the patch, called erbB2, and the apical side has a matching component called heregulin. Normally kept apart, they can be brought in contact when a breach occurs in the epithelial tissue.
*Together, they activate a complex series of steps leading to cell division and presto! the gap is filled in with another snug-fitting cell, and life goes on.
-- It is essential these active ingredients don’t mix at the wrong time. Too much cell division and you know what happens — cancer. Science Now has a news write-up on this story, and its discovery that is “so beautifully simple.”

A few more Cool Cell Tricks were reported recently: Cells have an exquisite toolkit for dealing with iron. Three New Zealand scientists writing a Perspective special feature in the Proceedings of the National Academy of Sciences describe a family of proteins called transferrins that clamp around iron and delicately transport this very toxic atom to wherever it’s needed in the cell. The clamp has a hinge that opens the structure and disgorges the iron when it is safe to do so.

Another protein called hemopexin transports heme by holding it in the center of a four-part structure.

Another Special Feature in the same issue talks about nitrogenase. Two Harvard chemists attack this puzzling molecule with the zeal of Captain Ahab pursuing Moby Dick (this is actually how they end their article), but in spite of the best efforts of scientists for decades, “Few problems in bioinorganic chemistry have proved as challenging and refractory.” They speak of techniques this molecule uses that are “biologically and chemically unprecedented,” and marvel. Hidden inside the inner sanctum of this molecular machine is a secret method for separating nitrogen atoms at room temperature that is the dream of agricultural chemists, because artificial nitrogen fixation (e.g., fertilizer making) is costly and energy intensive. “The synthetic problem of nitrogenase, nevertheless, remains unsolved,” but they think we’re getting warmer.

Current Biology for March 18 has a quick guide to a very versatile gene called APC (adenomatous polyposis coli), without which we either die or get colon cancer. It moves all over the cell, in and out of the nucleus, even riding the intracellular railroad. APC has many jobs. 

--It’s a potent tumor suppressor, 

--it regulates gene transcription, 

--and it has a role in “maintaining adherens junctions, and also helps to tether mitotic spindles to the cortex and to orient them in the epithelial plane. In mammalian cells, APC has been implicated in cell migration. APC also helps safeguard the fidelity of chromosome segregation in mitotic cells.”

Wow; a multi-talented kit. It appears to be essential for cell survival, too."
CEH