Brazilian scientists say they have produced human sperm cells in the testes of mice. The researchers extracted stem cells from the dental pulp of a human male volunteer, and injected the cells into the testes of male mice. Later they found that human sperm were being produced.

There’s no way to know at this point, with just a press release, whether the sperm was mature and functional. The scientists will present their research this week at the annual meeting of the European Society of Human Reproduction and Embryology in Barcelona. If this process works, it would seem simpler to put the cells in the man’s own testes.

The article notes in great understatement that the process of growing human sperm in a mouse “could, however, prove controversial because it gives a separate species an intimate role in human reproduction.”