How do skin cells make regularly spaced hairs in mammals and feathers in birds? Scientists had two opposing theories, but new research at the University of California, Berkeley surprisingly links them.
The first theory contends that the timing of specific gene activation dictates a cell's destiny and predetermines tissue structure -- for example, in the skin, gene activation determines whether a skin cell becomes a sweat gland cell or hair cell, or remains a skin cell. The second theory asserts that a cell's fate is determined instead by interacting with other cells and the material that it grows on.
Now, Berkeley researchers have found that the creation of feather follicles (like hair follicles) is initiated by cells exerting mechanical tension on each other, which then triggers the necessary changes in gene expression to create the follicles. Their results were recently reported in Science.
"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 first author Amy Shyer, PhD, a postdoctoral fellow in molecular and cell biology at the University of California, Berkeley, in a recent news release. "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."
The research team grew skin taken from week-old chicken eggs on different materials with varying stiffness. They found that the stiffness of the substrate material was critical to forming feather follicles -- material that was too stiff or too soft yielded only one follicle, whereas material with intermediate stiffness resulted in an orderly array of follicles.
"The fundamental tension between cells wanting to cluster together and their boundary resisting them is what allows you to create a spaced array of patterns," said co-author Alan Rodrigues, PhD, a biology consultant and former visiting scholar at Berkeley.
The researchers also showed that when the cells cluster together, this activated genes in those cells to generate a follicle and eventually a feather.
Although the study used chicken skin, the researchers suggest that they have discovered a basic mechanism, which may be used in the future to help grow artificial skin grafts that look like normal human skin with hair follicles and sweat pores.
Previously: New, stretchy material could lead to artificial muscle or skin, Stanford engineers create artificial skin that can signal pressure sensation to brain and Genetic secrets of youthful skin
Photo by Kecia O'Sullivan
