Note: Among cell populations of HF the folloving are the most important:
- Cells of epithelial origin: matrix trichocytes [M] and ORS [outer root sheath] cells.
- Cells of dermal origin: DP fibroblasts and dermal sheath [DS] fibroblasts.
The last play in HF predominantly regulation role, while the former represent mitotically active populations.


Model: DS +ORS +M represent in reality a HF with deleted or mechanically/ chemically detached DP.
1. So, in experiment vibrissae HF were dissected from surrounding tissue in situ and their DPs were micro-surgically dissected from their bottom. Thereafter vibrissae HF were placed back. As a result, 100 % of all vibrissae HF without DPs regenerate new DPs, produce several generations of hair shafts. First shafts were visually registered 15-24 days after operation.

R. F. OLIVER . Whisker growth after removal of the dermal papilla & lengths of follicle in the rat hooded rat .// J. Embryol. exp. Morph. Vol. . 15( 3) p. 331-347 , 1966.

2. The lower region of rat vibrissa follicles were wounded with a sharp tungsten needle. Following cell damage in the dermal papilla component hair growth ceased, and resumption of shaft production was always preceded by dermal papilla reformation from survived DP fibroblasts and partially from DS cells. .. Morphologically, regenerated hair shafts were normal.
If DP was destroyed completely, new DPs regenerate from DS cells, but hair fibre morphology was highly distorted.

JAHODA C.A. , R. F. OLIVER. Histological studies of the effects of wounding vibrissa follicles in the hooded rat . // J. Embriol. Exp. Morphol. Vol. 83 , p. 95-108. 1984.

3. If human HFs with dissected DPs were cultured in vitro alone, epithelial cells protrude from HFs into collagen gel like spikes.
If DP was mechanically detached from M, but still reside inside HF, trichocytes proliferate and migrate into cultured medium . Here they form folliculoid structures.
If basal membrane between M and DP was damaged by production of hair fibre stops completely.

ARASE. S ., SADAMOTO. Y ., et al. Co-culture of human hair follicles & dermal papillae in a collagen matrix . // J. Dermatol . 1990 vol. 17(11) . p 667-676 ,& Annals of the New York academy of sciences . vol. 642, p 454
ARASE. S., SHIKIJI. T., Experimental approaches for the reconstitution of hair in vitro . // 1994 vol.7 , p.12-15.

It can be concluded, that DS +ORS +M in situ is a self sufficient system to regenerate new DP and functionally active HF. But in vitro in this system, DS fibroblasts can’t change their status to a DP fibroblasts and no HF is regenerated.