What is Netrin-1?

• A. A lipid signaling molecule secreted by gut cells that promotes growth.
• B. A transcription factor in the nucleus that promotes growth when secreted.
• C. A protein secreted by gut epithelial cells that promotes cell growth when it binds to its receptor.
• D. A cytoskeletal protein involved in cell movement.

Answer: (C)

Netrin-1 is a secreted signaling protein that acts as a ligand binding to receptors on the surface of target cells, triggering intracellular pathways that promote growth, migration, or survival. In the gut, epithelial cells release netrin-1, and when it binds to receptors like DCC or UNC5 on surrounding cells, it stimulates growth signals. It is not a lipid, a transcription factor, or a cytoskeletal protein, so those descriptions don’t fit. Describing it as a protein secreted by gut epithelial cells that promotes cell growth upon receptor binding best captures what netrin-1 does.