For the first time, researchers at the University of Chicago describe in detail how neighboring skin cells adhere to one another to form sealed barriers. Without tight seals, the skin could not perform its primary function as a continuous barrier that keeps germs out and essential body fluids in.
Their findings were published in the January 21 issue of the journal Cell.
"We wanted to understand the molecular mechanisms that enable epithelial cells to bind to each other in order to form an impermeable barrier," said Valeri Vasioukhin, Ph.D., a postdoctoral fellow in the lab of Elaine Fuchs, Ph.D., Amgen Professor of molecular genetics & cell biology and biochemistry & molecular biology. Fuchs is an expert on epithelial cells and skin diseases.
The researchers used keratinocytes, a type of skin cell, to study the earliest stages of cell-cell binding. The first step to a tight bond between cells is the formation of what scientists call adherence junctions. These can be seen in fluorescence microscopy images as yellow dots on the outer membranes of adjacent cells. Scientists call these dots "puncta."
Because cell-cell adhesion is dependent on calcium concentration, Vasioukhin was able to capture cells in the act of forming puncta. Low levels of calcium inhibit cell-cell adhesion, enabling the scientists to monitor the adhesion process after adding calcium.
"What we saw as we raised the calcium concentration was the formation of two perfect rows of dots, or puncta, along the cell membranes between two adjacent cells," said Vasioukhin. Puncta on adjacent cells lined up perfectly with one another. The researchers named the matched puncta rows the "adhesion zipper."
Several hours after the calcium concentration was raised, Vasioukhin observed that some of the puncta in the rows fused into one dot. "It is as if the puncta are the teeth of a zipper, and when an adherence junction starts to form,
Contact: Sharon Parmet
University of Chicago Medical Center