Primary Hair Placode Cells (HF)

At E13.5, in response to Wnt, the first dermal signal, basal keratinocytes aggregate and commit to the hair placode cells fate. The resulting primary hair placode cells signal to the underlying dermis, triggering formation of dermal condensates that will coordinate further differentiation of hair-forming cells. In mouse, hair placode formation progresses through three successive waves: primary hair placodes form at E14.5 and produce guard hair, secondary hair placodes form at E16-17 and produce awl hair, and the third wave of hair follicle induction produces tertiary placodes and generate zig-zag hair.