Fig. 6. Cell behavior and cell fate organization in the HF matrix. The hypothesis of behavior and fate uncoupling. (A) Cell outlines were drawn from an optical confocal section of a HF from a farnesylated-GFP transgenic mouse in which GFP labels the cell membranes. The right side is the mirror image of the picture of the optical confocal slice. Cell behaviors are organized along the radial dimension of the matrix: the stem cells form a germinative layer juxtaposed to the DP (darkest colors). They undergo self-renewal and generate the transient progenitors in the second layer (in lighter colors). The next layers contain the postmitotic cells (lightest colors) that intercalate to produce columns. Cell fates are assigned according to the position of the stem cells along the proximodistal axis. Each structure is produced by several cells forming a sector. The most proximal cells are not involved in the formation of any inner structure; they are clonally related to the ORS (pink) (data not shown). Within a sector, the stem cells and the transient progenitors form a characteristic angle (63° for the IRS and 20° for the cuticle). This organization of matrix cells prefigures the organization of the HF in concentric layers (red arrows). Cell fates and cell behaviors therefore seem to be uncoupled and organized in two orthogonal systems. (B) Clonal hierarchy in the matrix (see text).