Fig. 7. The formation of the lateral disc from the lowermost tip of the outer root sheath (ORS). (A) In the mouse hair follicle (HF), the ORS envelops the hair bulb asymmetrically, forming a leading edge at the front of its downward growth. This lowermost extension of the ORS forms a specific pathway for downward-migrating bulge-derived cells (white arrow). (B) 2D section of the mouse HF at the same stage of cycling (late anagen). Bulge-derived cells gradually concentrate in the lowermost portion of the ORS, forming the lateral disc. The pressure of the perifollicular connective tissue sheath should force the gradual submersion of the enlarging lateral disc (red arrow) into the hair matrix. (C) The human HF at a late anagen stage. The substantial thickness of the lower ORS portion may be sufficient to harbor a distinct cell population of bulge-derived cells (red arrow) and thus the formation of separate lateral disc may be not necessary.
