New research at the University of California, Berkeley, indicates that the rubber-like elasticity of skin, which contracts to its original shape after being stretched, is key to the development of regularly spaced hairs and sweat glands during development.
The findings, published in a recent issue of Science, come from experiments on how chicken skin generates feathers as the embryo develops inside the egg. They could provide tips on how to grow artificial skin for grafts that looks like normal human skin, complete with hair follicles and sweat pores.
The research, according to the researchers, is the first to link the gentle tug of war among cells as an organism grows to the specific genes that turn on to make cells differentiate into different cell types, turning a generic skin cell, for example, into a specialized follicle cell and eventually a feather.
"The cells of the skin in the embryo are pulling on each other and eventually pull one another into little piles that each go on to become a follicle," said Amy Shyer, a postdoctoral fellow in the UC Berkeley Department of Molecular and Cell Biology.
"What is really key is that there isn't a particular genetic program that sets up this pattern. All of these cells are initially the same and they have the same genetic program, but their mechanical behavior produces a difference in the piled-up cells that flips a switch, forming a pattern of follicles in the skin."
In the study, as first authors, Shyer and Alan Rodrigues, an independent biologist and former UC Berkeley visiting scholar, tested different types of materials on which to grow skin taken from week-old chicken eggs, using artificial substrates that mimic the stiffness of tissues that underlie the skin in the bird.
The skin was obtained from chicken embryos at a time in their development analogous to about one month of gestation in humans, a point at which the human embryo looks the most like other animals, ranging from chickens and turtles to mice and humans, Shyer said.
This is also the point where the rough outlines of internal organs start to differentiate and look like, for example, a heart, lung or liver.
