Brain atlas aids CNS research
the GENSAT project, designed to track the maze of connections
between cells in the CNS.
Using a technique to insert fluorescently-labelled genes into live mice, researchers have created a new atlas that will allow neuroscientists to explore the maze of connections between cells in the central nervous system (CNS).
The atlas will enable scientists to determine when and where specific genes are switched on in the CNS, according to the researchers, led by Howard Hughes Medical Institute investigator Nathaniel Heintz and Mary Hatten at The Rockefeller University in the US.
To track gene expression, the researchers developed bacterial artificial chromosomes (BACs) that contained a single mouse gene found in the CNS, along with the regulatory segments that determine when and where it will be switched on and off. Instead of inserting only the mouse gene into the BAC, the researchers also spliced in a sequence that expressed a green fluorescent protein.
When the researchers introduce the BACs into CNS cells, the cells emit a green fluorescence if the genes the BAC contains are switched on. In addition, since the endogenous gene remains undisturbed, the labelled cells are otherwise normal and viable.
So far, the researchers have applied the technique to gather data on some 400 genes expressed in the CNS and they expect the database to grow at a rate of several hundred genes per year. The first results from the project have been published in the journal Nature.
The GENSAT BAC Transgenic Project will make available an atlas of micrographic images depicting the gene expression in the labelled cells, the library of BACs and the transgenic mice that contain the BACS.
"This project will give researchers an atlas of gene expression at a cellular resolution, which allows them to visualize and characterise novel cell populations and subpopulations that express a given gene," said Heintz. "This information will allow investigators to form very precise hypotheses about a gene's function based on from where and when it is expressed in the brain, which consists of thousands of types of cells."
The project will also provide experimental materials for neuroscientists. The library of BAC vectors will enable them to identify and access any major cell type in the brain, and the transgenic mice themselves will give neuroscientists animals in which specific living cells of interest are fluorescently-labelled, so that they can image, separate or electrophysiologically record from them.
In the Nature article, the researchers presented data on a variety of CNS genes to illustrate the utility of the atlas. The genes included those that code for lineage markers that reveal the location and development of specific subpopulations of CNS cells; guidance molecules that govern the wiring of neural circuitry during embryonic development; and molecules that enable researchers to trace the migration of neural cells during development of the brain and spinal cord.
For researchers studying neurological disorders, the atlas will enable dissection of molecular mechanisms and neural circuitry underlying those disorders, according to Heintz. "There are now many mouse models of neurodegenerative disease, such as Huntington's disease, that fairly accurately reproduce the symptoms seen in humans," he said. "Yet, in most cases, it's hard to know where the primary pathology lies - which cells are responsible for contributing to the primary effects in the disease."
Based on data provided by this atlas, investigators can express a mutant protein that causes a human disease in each of the cell types implicated in the disease, and find out which ones are primarily affected by this mutant gene product, he noted.
All data from the Gene Expression Nervous System Atlas (GENSAT) BAC Transgenic Project, will be available online to researchers worldwide at www.gensat.org.
