Figure 2. Spatiotemporal patterning of early hair cycles.
(A–D) Analysis of the whole mount dorsal skin samples from P0 (n = 3) (A) and P1 WT mice (n = 3) (A’) reveals subtle head-to-tail and lateral-to-medial hair cycle asynchronies. Asynchronies were inferred from examining the size of pigmented HFs. Larger HFs result from earlier anagen onset. (B) Heatmaps of skin samples from A and A’ built based on black pixel density (reflecting pigmented anagen HFs). (C) Quantification of anagen HFs at different phases confirms head-to-tail pattern asynchrony. Morphological definition of anagen phases used for this analysis is provided at the bottom on the panel. (D) Analysis of the whole mount dorsal skin samples from P0 220bpMsx2-hsplacZ mice, where lacZ reporter activates in anagen HFs starting from phase IIIb, confirms head-to-tail asynchrony. (E, F) Modeling rapid hair growth pattern evolution in the context of two heterogeneous domains. (E) Schematic depiction of the modeling conditions with central Dorsal domain flanked by two lateral Ventral sub-domains with coupling between Dorsal and Ventral HFs. (F) Compared to Dorsal domain HFs, Ventral domain HFs were assigned with higher levels of total available activator and inhibitor receptors, allowing shorter ~anagen and ~telogen duration. Furthermore, hair cycle asynchrony was introduced into Dorsal domain to model the initial head-to-tail asynchrony. In simulations, interactions between HFs across domain boundaries result in bilateral symmetry during the second cycle (simulated time t68-78.5). Also, initial asynchrony breaks down in the cycle 3 (t130), and partial bilateral symmetry maintains into the late cycles (see Appendix 2—video 4). Scale bars: A, A’, D – 5 mm. Images on A, A’ and D are composites.