AsianScientist (Mar. 1, 2018) – Scientists in Japan have engineered bioluminescent molecules for visualizing a host of biological processes in living organisms. They published their findings in Science.
Glowing creatures like fireflies and jellyfish are captivating to look at but also a boon for science, as they produce bioluminescent molecules that can be used for studying fundamental biological reactions. Bioluminescence is the result of a partnership: an enzyme—for example, luciferase, derived from fireflies—catalyzes the substrate D-luciferin, creating a green-yellow glow in the process. There has been considerable research to make this process more efficient. For example, swapping out luciferin for synthetic analogs and improving the rate of catalysis.
In this study, a team of scientists led by Dr. Atsushi Miyawaki at RIKEN, Japan, have created a bioluminescent molecule hundreds of times brighter than those conventionally used in laboratories. Based on previous work, the researchers knew that a synthetic luciferin called AkaLumine-HCl is able to penetrate the blood-brain barrier and produce a reddish light that is more easily seen in body tissues.
However, the synthetic luciferin was not very compatible with the natural luciferase, so the researchers successively mutated luciferase to improve the enzyme’s pairing with AkaLumine-HCl. The resulting Akaluc protein is both a more efficient catalyst for the substrate and more abundantly expressed by cells.
In the mouse brain, this combination of Akaluc catalyzing AkaLumine-HCl, dubbed AkaBLI, resulted in a bioluminescence signal 1,000 times stronger than that from the natural luciferase-luciferin reaction. Elsewhere in the body, just one or two glowing cells were clearly visible from within the mouse lung, something that could be useful for monitoring transplanted cells.
Persistent bioluminescence can be introduced easily by including AkaBLI in animals’ drinking water, although injecting the molecules yielded greater intensity.
“The fundamental improvement, though, is the practical applicability for in vivo physiological studies,” said Miyawaki.
With AkaBLI, how brain activity and structures change with behavior can be directly observed over time. In an experiment in which mice were exposed to familiar and new cage environments, the same neurons in the hippocampus could be recorded over multiple days.
“This is the first time such a small ensemble of a few dozen deep neurons related to a specific learning behavior can be visualized non-invasively,” said Miyawaki.
In a marmoset monkey, the researchers were able to track deep-brain neurons for more than a year using AkaBLI. The researchers highlighted that there is immense potential for this kind of stable and long-lasting bioluminescence for understanding neural circuitry during natural behaviors.
The article can be found at: Iwano et al. (2018) Single-cell Bioluminescence Imaging of Deep Tissue in Freely Moving Animals.
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