"Testicular germ cells appear to be able to mimic embryonic stem cells and become any cell in the body. The cells, called spermatogonial cells, are adult stem cells. They are the source of men's lifelong supply of sperm.
Now these cells may become the source of stem cells capable of treating a wide variety of illnesses, suggest Thomas Skutella and colleagues at the University of Tubingen, Germany.

The researchers biopsied the cells from human testes and grew them in laboratory cultures. When provided with the correct set of growth factors, the cells took on the characteristics of embryonic stem cells.

Depending on the chemical signals to which they were exposed, the stem cells were able to morph into any other kind of cell, including heart, bone, pancreas, and nerve cells.

"We have developed a culture method for establishing human adult germline stem cells from testicular biopsies," Skutella and colleagues report. "These cells changed their properties, losing characteristics of spermatogonial cells and acquiring characteristics similar to those of human embryonic stem cells."