P2.23 Defining a role for hairless by analytical comparison of differential gene expression

Hyunmi Kim, Andrew Engelhard, Karima Djabali, Andrey Panteleyev, and Angela M. Christiano

Departments of Dermatology and Genetics & Development, Columbia University, College of Physicians & Surgeons, New York, NY , USA

Mutations in the hairless (hr) gene in mouse and humans results in the loss of hair and the integrity of the hair follicle. The hr protein has been suggested to act as a transcription factor with a critical role during catagen, as indicated by hr mutations in humans and mouse models. hr is transcriptionally regulated by thyroid hormone in the brain, however, recent data from our laboratory indicates that it is not the major regulator of hr expression in the skin. Mouse models of other nuclear receptors such as knockouts of VDR and RXR suggest a possible regulatory pathway for hr, however, we have not found an interaction between VDR and RXR using multiple biochemical approaches.

In order to better understand the function of hr, we took a global, data driven approach toward determining hairless target genes and the possible pathway(s) hr functions. We used Affymetrix microarrays to compare the differential gene expression profiles of wild type mouse day 2 epidermis and rhino (rh^hr-/-) mouse day 2 epidermis. Using MAS5 and IBM Genes@Work software for supervised analysis, stringent parameters of two-fold or greater statistically significant values resulted in a list of 58 differentially expressed genes.  51 of these genes were found to be up-regulated by hr, while 7 genes were found to be down-regulated by hr. hr itself was found to be differentially regulated between these two populations, serving as an internal control. These genes can be organized into 9 main categories: extracellular matrix (12), cytoskeletal organization (4), cell cycle (3), signaling (4), proteolysis and peptidolysis (5), metabolism (4), transcriptional and translational regulation (5), unknown cDNA clones (5) and other (16).   Validation of the array has been performed using Real-Time PCR, in situ hybridization, and immunoflourescence, confirming the expression of these genes in murine neonate epidermis. Using pathway building software, these differentially genes were analyzed for possible pathway or regulatory relationships to one another as well as to hr in order to place hr in the context of a regulatory pathway.