Previously, we revealed how the underlying molecular mechanism of Bone Morphogenetic Protein (BMP) signaling governs the homeostasis of hair follicle stem cells (hfSCs) in vivo. Here, we focused on testing role of Id2 gene, one of the target genes which we identified to be downregulated in hfSCs after inhibition of BMP pathway. To test the function of Id2 gene in hfSCs in vivo we used Id2 gain of function approach (GOF) by generating transgenic mouse line. Our data demonstrated that Id2 overexpression in hfSCs results in prolonged telogen and a delay in anagen activation, maintaining stem cells quiescence. Further, we performed hfSCs sorting and RNA-seq analysis of GOF-Id2 hfSCs at first postnatal cycle. By comparison with common signature genes in quiescent bulge we demonstrated that approximately 10% of the genes were affected by overexpression of Id2 in hfSCs. Interestingly approximately half of those genes overlapped with common signature genes which previously we published to be affected by BMP pathway, thus working synergistically with that pathway. On the other hand our data also suggest that although Id2 is a direct target and an effector of BMP pathway in hfSCs in vivo, second half of those genes work at least partially independent from BMP signaling on gene regulatory network of quiescent bulge.

Recently, we revealed how the underlying molecular mechanism of Bone Morphogenetic Protein (BMP) signaling governs the homeostasis of hair follicle stem cells (hfSCs) in vivo. Here, we focused further on identifying the key interactions of Smads in canonical BMP signaling in hfSC regulation, using our recently developed inducible constitutively active Bmpr1a transgenic system. This allowed us to perform ChipSeq analysis in vivo in hfSCsand receive the predicted target lists for Smads for both p22 and p62 telogen hfSCs. Comparison of our previously published global genes expression where BMP signaling has been inhibited in hfSCs to all overlapped in vivo ChipSeq data between p22 v.s p62 revealed that approximately 72% of genes which previously has been 2 fold up or down regulated after BMP ablation in hfSCs were found directly regulated by BMP/Smads pathway. Previously, we identified Id2 gene as a target of BMP signaling in hfSCs with transcriptional downregulation following targeted BMP inhibition. Here, we confirmed that Id2 gene has been consistently present in our recent ChipSeq analysis both at p22 and p62, therefore, we decided to further test the functional role of the BMP effector, Id2 in hfSCs using an in vivo Id2 gain of function approach. Our data demonstrated that Id2 overexpression in hfSCs results in prolonged telogen and a delay in anagen activation, maintaining stem cells quiescence. Thus, we confirmed the functional role of Id2 gene as a direct target and effector of BMP pathway in hfSCs in vivo.