Analysis and meta-analysis of transcriptional profiling in human epidermis.

Because of its accessibility, skin has been among the first organs analyzed using DNA microarrays; psoriasis, melanomas, carcinomas, chronic wounds, and responses of epidermal keratinocytes in culture have been intensely investigated. Skin has everything: stem cells, differentiation, signaling, inflammation, hereditary diseases, etc. Here we provide step-by-step instructions for bioinformatics analysis of transcriptional profiling of skin. We also present methods for meta-analysis of transcription profiles from multiple contributors, available in public data repositories. Specifically, we describe the use of GCOS and RMAExpress programs for initial normalization and selection of differentially expressed genes and RankProd for meta-analysis of multiple related studies. We also describe DAVID and Lists2Networks programs for annotation of genes, and for statistically relevant identification of over- and underrepresented functional and biological categories in identified gene sets, as well as oPOSSUM for analysis of transcription factor binding sites in the promoter regions of gene sets. This work can serve as a primer for researchers embarking on skinomics, the comprehensive analysis of transcriptional changes in skin.