Nature recently published the first fruits of GENSAT (Gene Expression Nervous System Atlas), a project based at Rockefeller University that aims to provide a complete gene expression map of the mouse brain.

The project team are using a library of bacterial artificial chromosomes (BACs) to generate transgenic mouse lines in which the expression of a reporter gene recapitulates the expression pattern of an endogenous gene. The advantage of BACs over plasmid or viral gene transfer vectors is that they are large enough to accommodate entire genes, including all of their regulatory sequences. The reporter gene product fills the entire cell, so it is possible to study connectivity as well as gene expression.

So far, the expression patterns of around 150 genes have been mapped at various stages of development and postnatal life. The results can be found on the GENSAT web site. A table of the available histological images is provided for each gene. A mouse click on the relevant thumbnail rapidly brings up a larger image that can be scrutinized at single-cell resolution using the Image Navigator tool.

The database can be searched by gene name, and it also recognizes identification codes from other databases, including LocusLink or Genbank. Many of the images are annotated, and these annotations can be also searched to find genes that are expressed in specific brain structures and cell types.

Although reporter gene expression should precisely reproduce the native gene expression pattern in most cases, the researchers are verifying their results using more conventional techniques. The result will be a comprehensive atlas that is not only an invaluable resource for researchers, but is also fascinating to explore.