See-through animals are reducing the number of lab animals needed for each experiment.
Peering through a transparent window in the skin or skull allows Rakesh K. Jain, a cancer biologist at the Massachusetts General Hospital, to observe the growth of solid tumors in his mice. Called intravital microscopy, the technique has been around for several decades, and it’s one of several noninvasive technologies that are reducing the number of lab animals needed for each experiment. Whereas a typical study of cancer metastasis might require a sacrifice of one mouse every few days, these technologies allow researchers to observe the animals continuously, following as few as five mice.
To study entire systems rather than one discrete part, nude (hairless) mice are often used. Green fluorescent protein (GFP) might be injected into cultured cancer cells and then injected into the mice. When the mice are placed under specialized imaging machines, any sprouting tumors will emit a ghostly glow. For similar reasons, the zebrafish, which is transparent when young, has become a popular disease model; so too may a recently engineered transparent frog.
Using probes and sophisticated imaging technology, researchers can label specific cell types or even proteins and enzymes within cells—essentially a virtual dissection. Jain, for instance, uses probes to watch how cancer cells hijack the genetic machinery of normal cells.
In addition to saving animals, optical techniques reveal previously invisible information, often in real time. In studies of Alzheimer’s disease, two-photon microscopy movies have captured mouse neurons chatting among themselves, firing and spreading their dendrites like fingers reaching for one another in the dark.