Tiny lab-grown testicles look remarkably like the real thing under the microscope

Black and white microscope image of an artificial testicle which looks like a bundle of noodles.

For the first time, scientists have grown three-dimensional, miniature versions of testicles in the lab, using mouse cells. 

The lab-grown testicles survived in a dish for up to nine weeks and closely resembled natural mouse testicles, even developing tubelike structures equivalent to those that produce sperm in the testes of mice and humans. The cells within the model testicles also expressed genes similar to those that are active in regular mouse testicles.