Hailed as the most complex and exquisite structure in the universe, the human brain is generally considered to be without equal, yet new research suggests it may have finally met its match in the form of the lowly testicle. According to a study published today in the journal Royal Society Open Biology, our brains have a striking number of genes and proteins in common with the male gonads, and are in fact more akin to a goolie than any other organ in the body. In spite of its many talents, the brain has long been suspected of maintaining a hidden bond with the testicle, with previous research revealing links between intelligence and semen quality. Yet the extent of the kinship between these two wrinkly blobs has never been fully understood. To shine some light on the issue, the study authors compared the proteomes of 33 different tissue types, including the brain, testis, heart, ovaries, liver, prostate, cervix, and kidneys. Their results indicated that the brain is made up of 14,315 different proteins while the testis consists of 15,687, with the two tissues sharing an incredible 13,442 proteins in common. “The highest number of common proteins was observed between brain and testis, suggesting that human brain and testis are the most similar tissues of the human body,” wrote the researchers, before going on to explain that the two body parts also share a huge number of genes. “A large-scale analysis of the expression of 33,689 genes in 15 human tissues revealed that human brain and testis shared the greatest similarity in gene expression,” they revealed. As a consequence, brains and balls have a large number of functional similarities. For example, while the brain consists of neurons that are supported by glial cells, so too does the testis contain support cells, known as Sertoli cells. Interestingly, both glia and Sertoli cells produce lactate, which is used as an energy source by neurons and germ cells alike. The brain and the testicles also have extremely high energy demands, and are therefore particularly susceptible to oxidative stress. To counteract this weakness, the two tissues have developed similar protective barriers, called the blood-brain barrier and the blood-testis barrier. Many of the same receptor and signaling pathways are also found in both tissues, while a number of the common proteins are involved in a process called exocytosis, which refers to the movement of material from within a cell to the external environment and is an important feature of both brain and testis function. For instance, neurons rely on exocytosis in order to pass neurotransmitters to one another, while sperm cells use this same process when releasing compounds that allow them to fertilize eggs. How the brain got to be so much like a pair of cojones is not fully understood, although the study authors propose that it may be the product of a process called speciation. According to this theory, the same natural selection pressures that led to the emergence of humans as a distinct species helped to shape the development of both the brain and the testicle, cementing the relationship between these two apparently disparate tissues. And in case you’re wondering, this also applies to the brains of women, which are just as ball-like as those of men. Source
