That gonadal hormones influence bone remodelling has been well documented, but it is not the end of the story. Gerard Karsenty at Columbia University in New York and his colleagues have found that this influence runs in both directions — although only in males.

They show that the hormone osteocalcin, made by bone cells called osteoblasts, induces testosterone production by testicular Leydig cells, the body's key testosterone factories. The researchers demonstrate this in both mouse-cell cultures and live mice, and also identify an osteocalcin receptor expressed in Leydig cells but not in follicular cells of the ovary. Male mice engineered to lack this receptor are subfertile, as are male mice engineered to lack osteocalcin.

Cell 144, 796–809 (2011)