Two alumni of Dr. Rod Murphey’s laboratory have solved a long-standing problem in neuroscience. It has been known for 50 years that target-derived, retrograde signaling controls presynaptic transmitter release and thereby synaptic strength. Grae Davis and Brian Orr, a postdoctoral fellow in Grae’s lab at the University of California San Francisco (UCSF), have published a paper entitled "Retrograde semaphorin-plexin signalling drives homeostatic synaptic plasticity" in the October 5th issue of Nature (vol 550; pg 109-113) showing that semaphorin-2B is the retrograde factor that regulates synaptic strength. As Grae put it during his talk at the recent Max Planck Florida Institute Sunposium, “I have been working on this problem for 20 years and the signaling molecule was right in front me.” Grae Davis received his Ph.D. in Murphey’s lab in 1994 and has spent his career moving up the ranks at UCSF where he is now Chair of Biochemistry and Biophysics. Brian Orr received his Ph.D. in 2013 for work he did in Murphey’s lab at FAU. It is interesting that both Grae and Brian worked on this problem during their PhD work without solving it. Now their collaboration has solved the problem they were unable to solve in their previous lives.