All posts by: Sarah Hansen, M.S. '15

In the last few decades, the scientific community has produced mounting evidence that many animals can “see” with cells all over their bodies. What purposes do these cells serve and how do they work? Earlier this month, Tom Cronin, professor of biological sciences, described this phenomenon—where animals’ cells detect light (“photoreception”) for purposes other than image-forming vision—in an article for The Conversation, which has since appeared in outlets such as Scientific American, Salon, Inverse, and Flipboard and received more than 36,000 views.

“Many animals—including human beings—do have specialized light-detecting molecules in unexpected places,” Cronin writes, explaining that they’re most often found in cells in the central nervous system and skin, but also in blood and internal organs.

In humans, light-detecting cells are highly concentrated in the retina at the back of the eye. Scientists used to think that only the classic “rod” and “cone” cells involved in conscious vision detected light there. Cronin writes that in the early 2000s, “the discovery…of other cells in a mouse retina that respond to light came as a shock.”

All light-detecting cells contain proteins called opsins, and the newly discovered mouse eye cells contained a new type of opsin protein the researchers named melanopsin. The quest to find more opsins in other animals and in other body locations was on, and new technology made it much easier. Cronin explains, “The advent of inexpensive and efficient molecular genetic technologies has made the search for opsins a cottage industry in laboratories worldwide.”

Previously unknown light-detecting cells have now been found in animals from cuttlefish to birds, as well as in plants. “Now that we know that these photoreceptors can be found throughout animals’ bodies, what in the world are they actually doing?” asks Cronin.

Cuttlefish, octopus, and squid (cephalopods) have light-detecting cells called chromatophores all over their skin, he explains. Scientists understand these cells serve to “actively control their color or pattern for several reasons, most often for camouflage (to match the color and pattern of the background) or to produce bright, prominent signals for aggression or attracting a mate.”

The cells that detect light in plants are aptly named “cryptochromes,” reflecting the lingering mystery of how they work. Although scientists still have many questions about cryptochromes, they agree that they play a role in plant growth and annual reproductive cycles. Cryptochromes also appear able to assist some birds in navigation using Earth’s magnetic field.

In humans, photoreceptor cells that aren’t involved in conscious vision are known to regulate subconscious functions like pupil size, body temperature, and sleep-wake cycles. This helps explain why some blind people still have typical circadian rhythms.

Recent research has also indicated a possible role for non-image-forming vision in learning ability, mood, and the sensitivity of conscious vision, Cronin explains. Plus, melanopsin has been spotted in mouse blood. “Since humans are likely to have the same system,” he writes, “this could partially explain the increase in heart attacks in the morning, which are perhaps associated with blood pressure changes occurring at that time.”

Scientists have made notable progress toward understanding unconscious vision in the last few decades, but there is much left to learn. “We know nonvisual light detection is ubiquitous and significant in the lives of animals,” Cronin writes, and “future research will continue to untangle its effects on human health and well-being.”

Read Tom Cronin’s complete article, “Seeing without eyes—the unexpected world of nonvisual photoreception” at The Conversation.

Image: Two cuttlefish, which are known to have light-sensing cells throughout their skin. Photo by Joi Ito via Flickr, shared under CC BY 2.0.

UMBC biologist Erin Green has received a five-year, nearly $1 million grant from the National institutes of Health to examine how cells respond to environmental signals at the molecular level. Her work could provide clues to understanding processes as broad as how cancers take hold, the causes of autism, and aging.

“Any cell, in any species, is constantly bombarded with different signals from its environment,” says Green, assistant professor of biological sciences. Those signals, she explains, “have consequences for how the cell grows, whether it lives or dies, or if it stays as it is or turns into something else, like a cancer cell.”

Green studies epigenetic modifications—changes to DNA that do not involve a change in the sequence of bases (A, T, G, and C). Inside cells, long strands of DNA are wound tightly around proteins called histones. The modifications Green studies involve adding or removing small groups of atoms to the histones, influencing which sections of DNA are “unwound” and eventually translated into protein.

Epigenetic modifications can impact how genes are expressed within minutes, making them one of the fastest ways a cell can respond to environmental signals. “One challenge in the field, though, is directly linking specific modifications to environmental changes,” Green notes. There are many studies that correlate certain epigenetic changes with diseases or environmental conditions—from air pollution to in utero alcohol exposure—but figuring out exactly how the changes lead to complex health conditions has been much trickier.

Green’s work will explore the mechanism of a particular enzyme that adds methyl groups to histones, one of the most common epigenetic changes, using budding yeast as a model organism. Her enzyme is within a class of proteins that is also found in humans, and so far, she says, “many of the things that we know about them in humans started out in yeast research.” The human version of the enzyme Green is studying, a gene called MLL5, is already known to be expressed differently in some cancers, mutated in some cases of autism, and required for male fertility.

Why use yeast in her research? With yeast, Green explains, “we can test many conditions and look at the direct biochemical and molecular outcomes, which is much harder to do in other systems.” She’ll start by looking at how exposure to certain toxic oxygen compounds, a situation known as oxidative stress, affects the enzyme’s activity.

Green’s earlier work, supported by a UMBC START award, looked much more narrowly at a specific enzyme activity, but this new grant will allow her lab to paint with a broader brush. “We’ve been looking in a very targeted way,” she says. “By doing this bigger, more open-ended experiment we might uncover other things that would be good to look at. Are there other stress response pathways that this enzyme might be controlling?”

“I think having a system where we can directly answer these questions in a more controlled and easily manipulated environment is really powerful,” Green says. “If we’re able to…learn more about the function of this enzyme in yeast, that’s likely to give us a handle on what it might be doing in humans.”

Banner image: Erin Green. All photos by Marlayna Demond ’11 for UMBC.