a, Downwards extension of follicles during growth. Optical sections at three consecutive time points (3 h apart) of a growing live hair follicle shows the progeny compartment extending downwards (left three panels). The increase in the distances between nuclei, and total cell numbers were quantified within the stem cells and the progeny compartments (approximately anagen II to IIIa) (right panel, data are expressed as mean ± s.e.m., n = 13–20, P < 0.001; see also ). b, Reorganization of nuclei within the hair follicle. Two optical sections (left panels), corresponding traces and measurements (right panels) at the coronal and transverse planes (xy and xz) of the same follicle at time 0 and 4 h, respectively (approximately anagen II to IIIa) (bottom panels). c, Downwards migration of nuclei in the hair follicle during growth. Single optical sections showing complete (left panel) and lower partial views (top panels) of a single hair follicle at successive time points, 1 h apart. Red arrows in the optical slices and corresponding traces (bottom panels) mark a nucleus that is moving downwards, covering a distance of ~30 µm within 5 h (approximately anagen IIIb). DP, dermal papilla. Scale bars, 20 µm.