Mixed Signals Mixed Signals Ebrahim Zandi is pursing an understanding of the precise steps by which a signal is passed from outside a cell to its nucleus in order to turn specific genes on or off. And the goal he is now pursing with single-minded intensity is a thorough understanding of the precise steps by which a signal is passed from outside a cell to its nucleus in order to turn specific genes on or off.
Genes rely on signals for their marching orders.
For example, a gene that causes a cell to divide in two will never set that process in motion unless turned on by an outside stimulus. Once turned on, it will continue to promote proliferation until another signal turns it off. Most of the signals the genes rely on come from molecules outside the cell, however, and many of those molecules are unable to pierce the cell's sturdy lipid membrane. The only way such a molecule can get its message to the nucleus is by fitting into a receptor on the cell's surface and then prompting a cascade of chemicals called signaling molecules and transcription factors to carry the message along. That cascade is called signal transduction.