Figure 2. CLOCK–regulated genes are periodically expressed during hair follicle cycling.

(A) Temporal clusters (labeled 1–6 and color coded) of hair cycle-regulated transcriptional regulators. Transcription factors that play key roles in hair follicle morphogenesis and/or cycling are labeled with gene symbols in black. CLOCK-regulated genes are labeled in the blue box. Expression levels are from profiling data of the second hair growth cycle and are indicated by the colorimetric ratio-scale. (B) Time-course profiles of CLOCK-controlled genes during hair follicle morphogenesis, the first two natural and depilation-induced hair growth cycles. For each gene, the expression levels were normalized relative to the lowest expressed time point of the second cycle; the first cycle (P1 to P23) was normalized separately because different array was used for profiling. Differences in magnitude of change between the first and second cycles are primarily due to differential probe set efficiencies. Note the broken y-axis. E – embryonic days; P – postnatal days; D - depilation days. (C) Q-PCR of Dbp using independent samples from the first two synchronized hair growth cycles. Standard deviations were determined by using three replicates normalized to Gapdh and fold calculated relative to the lowest expression sample. For (B–D), time points are mapped based on histology to the corresponding phases of the cycle: hair follicle morphogenesis (M), anagen (A), catagen (C), and telogen (T).