Molecular Imaging Briefing

June 14, 2004



Imagine 3D images of the brain that describe patterns of gene expression for half the genes in the human genome and contain clues to their possible relationship with cancer, schizophrenia, or degenerative brain disease.

Researchers at the University of California, Los Angeles and the University of Southern California are producing 3D images of gene expression in excised mouse and human cadaver brains. The technique, called voxelization, combines micro-array gene expression technology and 3D biomedical imaging, according to senior investigator Desmond J. Smith, Ph.D., an assistant professor of molecular and medical pharmacology at UCLA's Crump Institute.

"It is conceptually similar to a CT scan or PET," Smith said. "But instead of one type of x-ray measuring one kind of quantity in the brain, it is like we have tens of thousands of x-rays, each tracking the expression level of a different gene."

Ten parallel sections of the subject's brain are processed through a miniaturized "printing press" that dices them into one microliter cube. RNA from each cube is fluorescently labeled, extracted, and then applied to a micro-array for gene expression analysis. The resulting 3D images provide a voxel-by-voxel 3D map of gene expression color-coded according to intensity.

The technique was developed by Smith, Simon Cherry, Ph.D, an associate director of the Crump Institute, and Richard M. Leahy, Ph.D, an electrical engineering professor at USC.

Voxelization experiments in 2002 identifiedfamilies of genes that are turned on or off in the striatum in a mouse model of Parkinson's disease, Smith said. He has also produced images describing the expression pattern of a dopamine D2 receptor gene in the striatum in the excised brain of a human cadaver (see figure).