Genetic Circuit
Secret of stripes
With multiple starting points, bacteria guided by a simple genetic circuit can create intricate patterns.
Many living things have stripes, but the developmental processes that create these and other patterns are complex and difficult to untangle. Now a team of scientists has designed a simple genetic circuit that creates a striped pattern that they can control by tweaking a single gene. "The essential components can be buried in a complex physiological context," said Terence Hwa, a professor of physics at the University of California, San Diego, and one of the leaders of the study published October 14 in Science. "Natural systems make all kinds of wonderful patterns, but the problem is you never know what's really controlling it." With genes taken from one species of bacterium and inserted into another, Hwa and colleagues from the University of Hong Kong assembled a genetic loop from two linked modules that senses how crowded a group of cells has become and responds by controlling their movements. One of the modules secretes a chemical signal called acyl-homoserine lactone (AHL). As the bacterial colony grows, AHL floods the accumulating cells, causing them to tumble in place rather than swim. Stuck in the agar of their dish, they pile up. Because AHL doesn't diffuse very far, a few cells escape and swim away to begin the process again.
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