What's My Line?

Here's the problem. You're a recently conceived embryo, barely more than ablob of nearly identical cells. But it's time to start divvying up the physiological chores required of a developing organism. And somebody's got to sign up for brain duty. Who gets the job?

The process is a mystery, but researchers are a step closer to solving it. They've identified a protein, called NRSF (for neuron-restrictive silencer factor), that plays cellular guidance counselor. When NRSF show up, one of a cell's possible career paths--becoming a brain cell--disappears.

The protein does its job in a blunt but effective manner. Building a brain cell requires particular genes useful only for neurons. But since each of our body's cells contains the same DNA, cells destined not to become neurons need a way to turn off those neuron-specific genes.

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Enter NRSF, which perches on the DNA near the relevant genes, blocking access like a beefy nightclub bouncer. its neuron genes rendered use, less, the cell pursues other career options.

NRSF is the first identified "silencer protein" that shuts off a whole set of genes specific to a cell type, says David J. Anderson, Ph.D., of the California Institute of Technology and the Howard Hughes Medical Institute. He and grad student Christopher Schoenherr have identified 18 genes that NRSF may control. But the question remains: What alerts NRSF to spring into action?

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