Stanford scientists have created a luminescent lab rat that, although not yet available in pet stores, offers plenty of scientific promise.

When its genes are "turned on," both literally and figuratively, the animal emits a green glow that can be detected by ultrasensitive camera.This molecular light switch will help scientists monitor gene therapy, track disease and monitor important developmental events like the growth of a long naked tail from a soft furry rump.

"This is a powerful approach for looking at any number of things because you can study gene regulation in a living animal over time, in superficial or deep tissues," said Dr. Christopher Contag, director of bioluminescence research at Stanford University School of Medicine.

The findings are published in the October issue of the scientific journal Photochemistry and Photobiology.

The idea originated in Japan, where the first generation of glowing mice were unveiled last June. But their scientific utility was untested.

The Japanese green mice were able to create several generations of green babies, the scientists said. Luminescent monkeys are just around the corner, they predicted.

Additionally, University of California at Davis researchers have been developing a glow-in-the-dark Christmas tree. They also aspire to create an oleander bush that, when planted down highway medians, would provide a wall of light for passing cars.

But the Stanford researchers are the first to develop a technique that enables them to observe the actual activation of a gene as it occurs in a living animal.

A gene is a set of instructions, that when activated, or "turned on," tells a cell exactly what to do.

Most genes perform mundane "housekeeping" chores, like the metabolic reactions inside all living cells.

But a few genes have far bigger jobs, coding for proteins that do things like manufacture insulin, fight off infectious organisms or store memories. These are the ones that interest Stanford scientists.