A question for the mad scientists out there

I just ran across this story about the world's first transgenic dog, a beagle puppy with sea anemone DNA that causes it to fluoresce red under ultraviolet light. If memory serves, this same trick was done previously with rabbits (although I think the bunnies glowed green rather than red).

What I haven't heard of yet is somebody creating a mammal that can glow without the UV light. Does anyone know if that would be technically possible, and if so, how much more difficult it would be?