Almost twenty five years ago, an ambitious international research project was initiated whose goal was to identify and map all of our genes. It took thirteen years to complete the Human Genome Project (HGP), which eventually revealed that we have around 20,000 genes that contain instructions for the production of proteins, or protein coding genes.
Proteins are essential components of all living things. They are some of the most structurally complex and functionally sophisticated molecules known to man, and they participate in virtually every process within cells. Although all cells in the body have the same DNA sequences, they don’t all express, or produce, the same proteins. Heart cells, for example, won’t synthesize an identical set of proteins as brain cells because they have different functions.
The collection of proteins produced in our bodies is known as the proteome, and while thousands of different proteins have been identified over the years, a comprehensive atlas of the proteins produced in different areas of the body did not exist. So just like how the HGP set out to map all of our genes, the Human Protein Atlas aimed to create a tissue-based map of all our proteins. To do this, they exposed donated samples from all major organs and tissues of the body to different sticky molecules called antibodies. If an antibody latched on to a target protein, it meant that it was expressed in the tissue.
Finally, after a decade of intense work by 13 different laboratories, the results are in. And guess what guys; your crown jewels contain more unique proteins than any other body tissue, even the brain. Testicles for the win.
More specifically, the project revealed that 77% of all human proteins are expressed in the testicles, and that these reproductive organs are home to 999 unique proteins. Our most powerful and sophisticated organ, the brain, was found to host only around 318. So why is that? Although the researchers can only speculate at this stage, they believe it could be due to the fact that producing sperm is a pretty complex procedure. That’s because it involves a special type of cell division, called meiosis, which results in cells containing half the amount of DNA as normal cells.
“What’s going on in the testes is unique,” explains project leader Mathias Uhlén, “as sperm must survive with half the chromosomes and outside the human body.” He adds that it’s possible ovaries have a similar number, but this is difficult to prove since eggs are produced inside fetuses.
Another interesting finding was that almost half of our genes produce proteins that are found in all different cells and organs of the body. These proteins, which are called housekeeping proteins, participate in processes that are essential to the functioning of all cells such as energy production and protein synthesis. Some 2,500 proteins, on the other hand, are uniquely produced in certain organs, meaning they must be involved in tissue-specific processes.
Alongside shedding light on our complicated bodies, this new wealth of information could have important implications for medicine as it should make the process of identifying faulty proteins easier.