Hair is important for temperature regulation, physical protection, sensory activity, seasonal camouflage, and social interactions. Hair is formed in hair follicles, which are complex mini-organs in the skin that are specialized for this purpose. All hair follicles are formed during fetal development, then new hair is generated in the hair follicle by continually undergoing phases of recession, rest, and growth throughout life.
The length of the hair is determined by the duration of the growth phase; for example, the growth phase for scalp hair can proceed for a number of years, while the growth phase for eyebrows last a few months.
After the growth phase, hair formation ceases, and the follicle recedes and enters a period of rest. After a period of rest, a new growth period starts, and the old hair is ejected and lost from the body. The reason for this complex regulation of hair growth is not understood, but it has been suggested that it makes it possible to adjust hair growth to the season.
In the present study Leif Carlsson’s research team identifies the transcription factor Lhx2 as an important regulator of hair formation. The Lhx2 gene is active during the hair follicle’s growth phase and is turned off during the resting period. The scientists have been able to show that Lhx2 is functionally involved in the formation of hair, as hair follicles in which Lhx2 has been inactivated cannot produce hair. Moreover, the activation of the Lhx2 gene in hair follicles has been shown to activate the growth phase and hence the formation of hair. Thus, Lhx2 is a gene that is important for the regulation of hair growth.
In stark contrast to previously published research findings from other teams of scientists, Leif Carlsson and his colleagues found that Lhx2 is primarily expressed outside the so-called bulge region of the hair follicle, where the follicle’s stem cells are found. The Umeå researchers have also shown that Lhx2 is necessary for the hair follicle’s growth (anagen) phase to proceed and for the hair follicle’s structuring. Moreover, transgenic expression of Lhx2 after birth is sufficient to activate the growth phase and stimulate hair growth.
These findings allow for an alternative interpretation of the function of Lhx2 in hair follicles compared with previous results. Lhx2 is expressed periodically, primarily in precursor cells that are distinct from the cells in the bulging region of the follicles. It is a factor that is necessary for hair to be formed and to grow.