Morse and his team discovered that nerve signals to the reflective cells trigger the addition of phosphate groups to the links. Normally, the links between the beads are strongly positively charged, so they repel each other, straightening out the proteins like uncooked spaghetti.
#Squids next door series
Reflectin, which is contained in closely packed layers of membrane in iridocytes, looks a bit like a series of beads on a string, the researchers found. "Instead, our evidence showed that the features of the reflectins that control its signal detection and the resulting assembly are spread across the entire protein chain." The group had expected to find one or two spots on the protein that controlled its activity, he said. "The results were very surprising," said first author Robert Levenson, a postdoctoral researcher in Morse's lab. Thanks to a combination of genetic engineering and biophysical analyses, the scientists found the answer, and it turned out to be a mechanism far more elegant and powerful than previously imagined. Reflectin proteins are behind these features' ability to shapeshift, and the researchers' task was to figure out how they do the job. As these structures change their dimensions, the colors change. Light bounces between nanometer-sized features about the same size as wavelengths in the visible part of the spectrum, producing colors. Unlike the color from pigments, the highly dynamic hues of the opalescent inshore squid result from changing the iridocyte's structure itself.
#Squids next door skin
Together, these layers of pigment-containing and light-reflecting cells give the squids the ability to control the brightness, color and hue of their skin over a remarkably broad palette. The squids also have leucophores, which control the reflectance of white light. One group of cells controls their color by expanding and contracting cells in their skin that contain sacks of pigment.īehind these pigment cells are a layer of iridescent cells - those iridocytes - that reflect light and contribute to the animals' color across the entire visible spectrum. Tiny muscles manipulate the skin texture while pigments and iridescent cells affect its appearance. Like most cephalopods, opalescent inshore squid, practice their sorcery by way of what may be the most sophisticated skin found anywhere in nature. Understanding this mechanism, he said, would provide insight into the tunable control of emergent properties, which could open the door to the next generation of bio-inspired synthetic materials. "We wanted now to understand how this remarkable molecular machine works," said Morse, a Distinguished Emeritus Professor in the Department of Molecular, Cellular and Developmental Biology, and principal author of a paper that appears in the Journal of Biological Chemistry. But still a mystery was how the reflectins actually worked. In previous work, the researchers uncovered that specialized proteins, called reflectins, control reflective pigment cells - iridocytes - which in turn contribute to changing the overall visibility and appearance of the creature. This enables them to communicate, as well as hide in plain sight in the bright and often featureless upper ocean. Also known as the California market squid, these animals have evolved the ability to finely and continuously tune their color and sheen to a degree unrivaled in other creatures. Researchers in the lab of UC Santa Barbara professor Daniel Morse have long been interested in the optical properties of color-changing animals, and they are particularly intrigued by the opalescent inshore squid.
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