They compared proteins across 33 tissue types, including the heart, intestine, cervix, ovaries and placenta, and found that testes and brains share 13,442 proteins in common. This is corroborated by gene expression studies showing these two distantly positioned organs share the highest number of genes among all the organs in the body. Taking a closer look at the shared proteins most highly expressed in these tissues, Matos and colleagues found they’re mostly involved in tissue development and cell communication. These shared proteins make sense when you consider how unexpectedly similar the two tissues are in many ways, the team explains. The brain and testes are both greedy for energy to fuel highly demanding processes like thinking and the production of several million little sperms per day. So both organs have specialized cells to support the hard-working neurons in the brain and germ cells in the testes – to keep them well fed and physically comfortable. Also, despite being very differently purposed cells, neurons function similarly to sperm in several ways. Both cells have important tasks involving moving stuff from within themselves to their outside environment – a process called exocytosis. This is how brain cells pass neurotransmitters between each other. In sperm, the same process is used to release important fertilization factors. In neurons, exocytosis is also involved in the growth of their reaching little branching arms collectively called neurites (dendrites and axons), while in sperm this process allows its innards to fuse with an egg. “This is an underexplored topic, and the connection between these tissues needs to be clarified, which could help to understand the dysfunctions affecting brain and testis,” the team wrote.