Posted on: February 10, 2009
New study originating from the laboratory of Dr. Elane Fuchs at Rockefeller University provides further insight into how hair follicles enter growth phase (anagen). In their work, Dr. Fuchs and her team focused on so-called hair germ cells, which are believed to be direct progeny of actual hair follicle stem cells. During new hair growth initiation, hair germ cells are the first to be activated to proliferate, followed by activation of bulge stem cells.
Through a series of experiments scientists confirmed that both bulge stem cells and secondary hair germ cells are molecularly very similar, suggesting that the germ does indeed originate from the bulge.
"We discovered that the dynamics of the hair follicle regeneration is a two-step process," says Valentina Greco, a visiting postdoctoral fellow who, along with postdoctoral associate Ting Chen, spearheaded the project. "The hair germ, which is in constant contact with the dermal papilla, gets activated first and the bulge is then called to contribute later during growth."
"Because the germ is in closer proximity to the dermal papilla, it may achieve a threshold of stimulatory signals sooner than the bulge," explains Dr. Fuchs. Previous work by her team has shown that two inhibitory signals, known as Wnts and BMP, are needed for hair follicle stem cells to activate. They have now identified an additional activation signal, a growth factor called FGF7, that is made by the dermal papilla and steadily increases throughout the resting phase. "We think that FGF7 might contribute, along with the Wnts and BMP inhibitory signals, to coax the hair germ to divide and proliferate," says Fuchs.
The dual organization makes sense, explains Greco, since unlike the bulge stem cells, hair germ cells respond and proliferate quickly but soon exhaust their proliferative potential. "This organization prevents depletion of the bulge stem cells, which are long-lived," says Greco. "It also allows a rapid initial proliferation of the hair follicles."
For more information, please visit: Cell Stem Cell article website
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