Our brains are arguably one of evolution’s greatest achievements, composed of many regions that each have unique configurations of cells and patterns of connectivity that together bestow us our mental prowess. But what is it about our genes that makes this organ so distinct from those of others? New research from scientists at the Allen Institute is offering us some insight, discovering that a relatively small number of gene expression patterns seem to predominate in the brain, and that these appear to be common, or conserved, among humans.
“So much research focuses on the variations between individuals, but we turned that question on its head to ask, what makes us similar?” lead researcher Ed Lein said in a statement. “What is the conserved element among all of us that must give rise to our unique cognitive abilities and human traits?”
The reasoning behind such an approach is that if some core pattern of gene expression appears to exist across humans, one that seems to be true for multiple brain regions, then perhaps this “default” network of genes could help us understand how the structure and function of the brain is so conserved. Furthermore, scientists could then look for deviations from this that could help explain various mental health problems or diseases affecting the brain, like schizophrenia or epilepsy.
If a gene is expressed, it basically means it is “switched on” and being actively turned into a protein by machinery in the cell. To look for the existence of expression patterns in the brain, the researchers made use of a bank of open-access data called the Allen Human Brain Atlas. Scouring the genes of six individual brains, the team sought to identify those with consistent expression patterning across different structures, 132 of which were scrutinized. Next, they looked at the relationships between these genes and also with brain function and disease.
Describing their findings in Nature Neuroscience, despite there being some 20,000 genes coiled up into our chromosomes, their patterns of activity in the brain could be characterized by just 32 expression “signatures.” These represented different cell types, the components inside the cells and links with disease, both neurodevelopmental (like autism) and neurodegenerative (like Alzheimer’s).
While members of some of these identified gene networks were similar in mice, a species regularly used for comparison, many differences were also observed. Unexpectedly, genes expressed in cells that play support roles in the brain tended to be the most preserved across the two species, compared with those found in neurons. Conversely, genes that tended to show the highest levels of consistency across brains were those associated with disease and already targeted by drugs. So not only are these findings helping to unravel the underlying genetic mechanisms of what makes our brain unique, but they could also help us find new treatments for diseases affecting this organ.