3D map of gene expression in the brain

Research published online in Nature last week has revealed new information about the structural and cellular complexity of the brain. It is hoped the research can be used to facilitate brain research all over the world.

The Allen Brain Atlas is a web-based three dimensional map of gene activity in the mouse brain, documenting expression of more than 21,000 genes at the cellular level. Our genome operates by sending instructions from DNA in the form of mRNA for the manufacture of proteins. To make the map, Ed Lein and colleagues at the Allen Institute for Brain Science in Seattle took thin slices of tissue from different parts of the mouse brain and used a technique called 'in situ hybridisation' to label a specific mRNA to show where a gene is being expressed. This was repeated for nearly every gene in the mouse genome. A map of gene activity throughout the brain was then compiled and is now available as an open-access database.

The technique used to create the atlas identified all well-known brain cell markers, and also revealed many previously undiscovered markers of different cell types. The study shows that 80 per cent of all genes are expressed in the brain, compared to the predicted 60 per cent, however, most are expressed in only about 25 per cent of cells and may not be detected by other available techniques. The data has also revealed differing levels of expression of genes within the same cell type, suggesting these groups of cells may have different functions in the brain.

The functions and characteristics of a cell are determined by the subset of genes being expressed within it. A map such as this may lead to a better understanding of the cell-type specific functions in the normal brain, as well as in diseases in which certain brain cell-types are dysfunctional, such as Alzheimer's or autism. 'This landmark paper represents the first attempt to see what we can learn from a global analysis of gene expression across the entire brain' said Mark Tessier-Lavigne, chairman of the Allen Brain Atlas Scientific Advisory Board. 'The completion of the Allen Brain Atlas represents a huge leap forward in one of the great frontiers of medical science - the brain'.