In the Human Protein Atlas, there are 32 human organs and tissues analyzed. 2489 of the genes have significantly higher expression in one tissue compared to all other tissue types. Analysis show that testis is the organ with the largest number of tissue-enriched genes, with 1057 genes classified as testis enriched. The specific events and alterations of cell structure during spermatogenesis, and the fact that sperm has the ability to survive outside the male body may explain why testis has the largest number of enriched genes.

The organ with the second highest number of enriched genes is the brain with 381 enriched genes. The list of brain enriched genes is anticipated to become longer as additional areas of the brain are analyzed.

For most tissues, including testis and brain, the fraction of transcripts of the enriched genes is about 10%. However, for pancreas and liver with 37 and 170 tissue enriched genes respectively, these genes represent 64% and 28% of the pancreas and liver transcript pool, respectively. This demonstrates the extreme specialization of these two organs for production of secreted proteins.

For an interactive version of the figure go to The Human Protein Atlas