For just a few hours, shimmering waves of calcium move through cells in the developing eyes of fruit flies. These spontaneous waves serve a purpose, enabling communication between cells and shaping the eye structure, according to a new study published in Science .
Scientists have long observed waves of calcium during the development of the visual system in humans and other mammals. These waves occur in the retina—the inner layer of the eye that senses light and transmits signals to the brain—well before the eyes can detect light or see. Scientists believe that these waves of calcium activity refine connections in the developing visual brain, yet their potential role in building the physical architecture of the eye itself had not been previously explored.
Now, New York University researchers have discovered that fruit flies also have these waves of calcium activity, or "retinal waves," during development. This synchronized activity shapes their growing eyes, creating a precisely ordered architecture that later enables them to see.
"This discovery uncovers a universal developmental mechanism where synchronized calcium activity shapes tissues to achieve precise sensory function," said Ben Jiwon Choi, a postdoctoral fellow in NYU's Department of Biology and the study's lead author.
"Our study shows that these long-seen retinal waves, in addition to coordinating neuronal circuitry, also play a key role in shaping the developing eye," said Claude Desplan, professor of biology and neural science at NYU and the study's senior author.
Fruit flies are an important species for biological research, given that they share roughly 75 percent of the genes that cause disease in humans. In studying the developing eyes of flies, NYU researchers observed that retinal waves begin when calcium is released from intracellular stores. The waves then move across cells through channels between cells called gap junctions. Notably, while calcium is usually a sign of neural activity, the retinal waves are found in non-neuronal retinal cells that build the eye's structure, not in neurons.
The researchers found that these waves generate retina-wide calcium patterns that sculpt the eye's surface, leading to the formation of a uniform and optimized architecture that supports precise vision.
"These retinal waves appear to determine the shape of the eye itself and prepare the eye to be able to see later on," said Desplan.
The researchers noticed that the waves of activity were biased toward the lower part of the fly's eye—the part that sees the ground and therefore receives less light. As a result, the lower part of the fly's eye develops larger lenses to capture more light, while the upper part of the eye develops smaller lenses.
"These waves allow the eye, which develops in a very fixed manner, to adapt the shape of its different parts that see the sky or the ground," added Desplan.
In addition to Choi and Desplan, Yen-Chung Chen is a study author. The work was supported by the National Institutes of Health (EY13010, EY017916, F32EY027682), NYU's MacCracken Fellowship, the New York State Stem Cell Science program (NYSTEM), and the Taiwan Ministry of Education.
