The discovery of a second form of phototransduction light sensing in cells that is derived from vitamin B2 could reveal new information about cellular processes controlled by light. Phototransduction – the conversion of light signals into electrical signals in photoreceptive neurons – was believed for many years to be solely based on a chemical derived from vitamin A called retinal. Now, however, scientists from the University of California have determined that phototransduction also can be mediated “by cryptochrome, a protein that uses a B2 vitamin chemical derivative for light sensing. The image shows blue-light-sensing arousal neurons, which for the first time have been linked to rapid phototransduction. Courtesy of the University of California, Irvine. Cryptochromes are blue-light photoreceptors found in circadian and arousal neurons that help to regulate slow biochemical processes. For the first time, these proteins have been linked to rapid phototransduction. The findings open the door to opportunities to adapt light-sensing proteins that could drive medically relevant cellular activities, the investigators say. The breakthrough – “which literally and figuratively came ‘out of the blue,’ ” said researcher Todd C. Holmes – has implications in the field of optogenetics. It is currently being used to understand how treatments like deep brain massage can aid people with neurodegenerative diseases. The team found that cryptochrome mediates phototransduction directly in fruit fly circadian and arousal neurons in response to wavelengths of blue light. In addition, the investigators genetically expressed the protein in the neurons that are not ordinarily electrically responsive to light to make them light responsive. Their work appears in the March 3, 2011, online Express site for the journal Science.