Despite its importance, scientists still do not understand all of the different cell types that make up the brain.
A group of researchers from Baylor College of Medicine (Drs. Andreas and Kimberley Tolias' laboratories), the Karolinska Institutet (Dr. Rickard Sandberg’s laboratory), and the University of Tübingen (Dr. Matthias Bethge’s laboratory) have developed a novel technique that allows, for the first time, the anatomical and functional properties of single neurons to be directly linked to their gene expression profiles.
For years, scientists have used a technique known as whole-cell patch-clamp recording to measure the electrical activity of neurons, including their unique patterns of activation and their connectivity to other neurons, and to relate these physiological properties to the cell’s morphology.
However, individual neurons also differ at the genetic level. While all cells within an organism have the same genetic ‘blueprint’ of DNA, each individual cell only uses a subset of the available genes, which are ‘expressed’ in the form of mRNA and ultimately proteins.
Until now, techniques to study genetic variability at the single-cell level have been impossible to combine with patch-clamp recording, and thus it has been difficult for neuroscientists to directly relate cellular physiology with gene expression profiles.
A multidisciplinary team led by Dr. Andreas S. Tolias, associate professor of neuroscience at Baylor, and Dr. Rickard Sandberg, professor of molecular genetics at the Karolinska Institute, developed a new method called ‘patch-seq’ that combines patch-clamp recording with single-cell RNA sequencing to study the morphology, physiology and gene expression profiles of individual neurons.
Their study focused on the outermost, very thin layer of the neocortex, which is known to contain two morphologically distinct types of neurons.
Said Cathryn R. Cadwell, student in the M.D/Ph.D program at Baylor and co-first author:
“We found that individual neurons express approximately 7,000 genes. Many of these genes are thought to be important for specifying the morphological and physiological characteristics of a neuron."
Added co-first author Athanasia Palasantza of Karolinska Institutet:
“The patterns in gene expression were used to sort cells into two genetic classes, which corresponded almost perfectly to the two known morphological cell types. In addition, several quantitative physiological properties of the neurons could be predicted based on their gene expression profiles."
Interestingly, the study also found that four genes that have been previously associated with autism and schizophrenia were expressed by neurons of a particular cell type.
Sandberg and Tolias believe that their technique can allow a systematic identification of the specific brain cell types that may be dysregulated in neuropsychiatric illness. This can provide a novel path forward for developing cell-types specific therapeutic interventions.
Cathryn R Cadwell, et al. Electrophysiological, transcriptomic and morphologic profiling of single neurons using Patch-seq Nature Biotechnology (2015) doi:10.1038/nbt.3445
Photo: Rick Bolin