Abstract
One of the least anticipated and less heralded outcomes of mouse genetics has been to rediscover whole organism physiology. Among the many unexpected findings that it has brought to our attention has been the realization that gut-derived serotonin is a hormone-inhibiting bone formation. The importance of this discovery presented in this review is 2-fold. First, it provides a molecular explanation for 2 human genetic diseases-osteoporosis, pseudoglioma, and high bone mass syndrome; second, it suggests a novel and anabolic way to treat osteoporosis. These findings illustrate the importance of the gastrointestinal tract in the regulation of organ physiology at yet another extraluminal site.