Figure 2. BMP restricts the Shh-expressing IRS progenitor pool.

(A) Experimental timeline for selectively targeting Bmpr1a ablation in Shh-expressing TACs during full-anagen. (B–D) BMPR1a loss results in an expansion of YFP⁺ cKO TACs and an increase in their proliferation. (E) Lineage tracing of YFP⁺ TAC progeny. (F and G) Differential distribution of YFP⁺ progeny reveals an increase in AE15⁺ IRS and decrease in AE13⁺ cortex following Bmpr1a ablation in TACs. (H) Bmpr1a-null YFP⁺ TACs lineage trace to AE15⁺ IRS but not AE13⁺ cortex. (I) Axin2-LacZ activity in Shh-expressing TACs, DP and cortex/medulla. Note lack of X-Gal staining (blue) in HS developing from Bmpr1a-targeted side. (J) LEF1+ TACs are expanded upon BMPR1a loss, but LEF1+ cortex is absent. (K) Shh⁺ IRS TACs are expanded and express elevated Shh in the absence of BMP signaling. (L) GATA3⁺ cells are expanded following Bmpr1a ablation in Shh⁺ TACs. (M and N) Lineage tracing of YFP⁺ progeny following Gata3 ablation in Shh⁺ TACs. Following loss of GATA3, AE15+ IRS progeny (external to the K82⁺ HS cuticle) are lost, while AE15+ HS progeny (internal to K82) are expanded. (O) Gata3 ablation in Shh⁺ TACs leads to an expanded cortical layer (AE13+) and smaller AE15+ IRS. (P) EM of Gata3 straight KO HFs reveals absence of IRS lineage. (Q) Proliferation is unaffected following Gata3 ablation in TACs. Data are represented as mean±SEM. * = p<0.05, ** = p<0.01, *** = p<0.001, Students t-test. Scale bar = 25 μm.