Map Model Understanding how ELF-1 and Mek4 interact to produce topographic connections in the visual system could shed light on other regions of the brain. The discovery could ultimately lead to new ways of repairing damaged nerve connections. In reconstructing connections, it's not enough to have nerves survive and grow. Flanagan was not looking for the elusive molecules that guide the wiring of the brain and the retina when he began his work on the matching receptor and ligand. In the course of this quest, Flanagan became intrigued by a family of receptor molecules-the Eph subfamily of tyrosine kinase receptors.
Receptors are proteins that typically sit on the surface of cells and bind molecules called ligands.
But it was not known which ligands were binding to the two Eph receptors. Nor was it clear what the receptor-ligand pairs might be doing in the embryo. When the protein found a li-gand to bind to, the tag would produce a color, showing where the ligand was located. Ordinarily, the next step would have been to clone and identify the ligand and find out where in the embryo it was located. This was an idea that had been floating around for a long time.