Tissue-Specific Protein Expression in Human Cells, Tissues and Organs

An important part of understanding human biology is the study of tissue-speci fi c expression both at the gene and protein level. In this study, the analysis of tissue speci fi c protein expression was performed based on tissue micro array data available on the public Human Protein Atlas database (www.proteinatlas.org). An analysis of human proteins, corresponding to approximately one third of the protein-encoding genes, was carried out in 65 human tissues and cell types. The spatial distribution and relative abundance of 6,678 human proteins, were analyzed in different cell populations from various organs and tissues in the human body using unsupervised methods, such as hierarchical clustering and principal component analysis, as well as with supervised methods (Breiman, 2001). Well-known markers, such as neuromodulin for the central nervous system, keratin 20 for gastrointestinal tract and CD45 for hematopoietic cells, were identi fi ed as tissue-speci fi c. Proteins expressed in a tissue-speci fi c manner were identi fi ed for cells in all of the investigated tissues, including the central nervous system, hematopoietic system, squamous epithelium, mesenchymal cells and cells from the gastrointestinal tract. Several proteins not yet associated with tissue-speci fi city were identi fi ed, providing starting points for further studies to explore tissue-speci fi c functions. This includes proteins with no known function, such as ZNF509 expressed in CNS and C1orf201 expressed in the gastro-intestinal tract. In general, the majority of the gene products are expressed in a ubiquitous manner and few proteins are detected exclusively in cells from a particular tissue class, as exempli fi ed by less than 1% of the analyzed proteins found only in the brain.

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