Functional mapping of the mouse hairless gene promoter region

The mouse hairless gene (Hr) encodes a protein of 127 kDa, acting as corepressor of nuclear hormone receptors. The Hairless protein (HR) is involved in the control of the cellular transition to the first hair cycle in adult Mammals. In its absence hair follicles disintegrate leading to a complete and irreversible hair loss with formation of cutaneous cysts. The hairless phenotype is therefore linked to defective proliferation and migration of the hair follicle stem cells apparently unable to respond to various signalling molecules. The Hr gene is expressed at high levels in skin and brain, and hairless transcripts were detected in gonads, thymus and colon. Although the patterns of Hr expression appear to be spatially and temporally regulated, very little is known about the molecular basis of the transcriptional control underlying Hr gene function. In this work we determine the precise transcriptional initiation start site of the mouse Hr gene and identify a new 1,1 kb cis-control element (RE1) that encompasses the promoter region and is able to drive luciferase reporter expression in skin and brain derived cell lines. We performed a deletion analysis and explored functionally regulatory motifs within this fragment to show that the role of this upstream regulatory region is linked to the presence of TRE and VDRE binding sites. We find that a TRE situated at -300 bp from the cap site is essential for gene expression in both skin NIH 3T3 and GHFT1 cells, while a VDRE positioned 94 bp upstream of the TRE modulates reporter expression specifically in skin derived cell lines. In addition, we define a novel cis-regulatory motif UE60, situated at the 5-end of RE1 and likely to interact with both TRE and VDRE. Our data complete previous results on the possible existence of an autoregulatory pathway, implicated in Hr gene regulation. Taken together these findings reveal a complex molecular network that potentially links several signalling pathways in hair follicle formation. We discuss the organisation of the regulatory modules in the mouse Hr gene upstream DNA sequences in the light of the high homology of this region in mouse, rat and human.