The Mosaic Brain Dr. Jerold Chun is getting to the bottom of Alzheimer’s disease one neuron at time The human brain is an enormously intricate mosaic. With mosaics, you have to assemble the pieces one at a time to see the big picture,” says Jerold Chun, M.D., Ph.D., professor and senior vice president of Sanford Burnham Prebys (SBP) Neuroscience Drug Discovery Program. “By understanding these brain pieces—single neurons—we will see the bigger picture of the brain, its diseases and how to treat them.” Chun, a pioneer in neuroscience, recently joined our Institute, bringing his 25-member research team with him from The Scripps Research Institute. The diligent and bright young students and postdocs specialize in genomic mosaicism, the DNA differences among cells of our brain and body. “People used to think that each cell in the body had the exact same genetic makeup—23 pairs of chromosomes, identical copies of genes and DNA sequences,” Chun explains. “But with modern technology to analyze singlecell genomes, we now realize that cells from the same person can actually have different genomes, creating a genomic mosaic.” Chun’s lab was the first to show that cells with altered DNA content that includes more or less than two copies of each chromosome—aneuploid cells—are found in the brain. Before then, DNA was thought to be identical in every brain cell. “In the brain, each neuron is unique, which contributes to the overall picture of how this remarkable organ controls our thoughts and all of our body’s functions,” says Chun. Jerold Chun, M.D., Ph.D., is professor and senior vice president of the Neuroscience Drug Discovery Program.