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Wiring the Brain: Basic Properties of Guidance Molecules

NEURO-BBGRYP

Like signs on a highway, guidance cues signal to growing axons where to go, where to stop, where to turn around, and where to pause. Guidance cues are commonly divided into four classes of molecules: chemoattractants, chemorepellents, contact attractants, and contact repellents.

Which of the following describes a chemorepellent molecule?

A

A secreted protein that establishes a gradient around axons' intended targets with a high concentration close to the target and low concentration further away from the target.

B

A glycoprotein component of the extracellular matrix that forms a sharp boundary across which axons cannot grow.

C

A protein molecule expressed in a gradient along a pathway that many axons take. This protein makes some, but not all, axons turn away from areas where it is expressed, depending on whether such axons have necessary receptors to sense it.

D

A protein molecule expressed in a gradient along a pathway that many axons take. If an axon has a receptor for this protein, it will turn toward it; all other axons will ignore its presence and keep growing straight.