Transcriptomics from single cells

New technologies are making it possible to measure gene expression from single cells. Reverse transcriptase is used to convert the few picograms of mRNA in a cell to cDNA. Next generation sequencing methods, such as SOLiD sequencing, provide a low cost means to sequence the cDNA allowing quantification as well as genotyping. Unlike RT-PCR which enables single cell measurement of one or a limited number of transcripts, the entire transcriptome can be accessed. It will be possible to discover new correlations between genes and their role in diseases. We have begun testing this method on a variety of cell types including cultured cancer cells and human stem cells. Methods are in development to test circulating cancer cells. Progress has also been made on a different technology that addresses genotyping of the genomic DNA from one cell. Whole genome amplification by a method called Multiple Displacement Amplification (MDA) provides sufficient DNA for use in sequencing and genotyping. This enables analysis of unexpressed regions of the genome which are lost in transcriptional studies. Together, single cell methods for transcriptomics and genotyping of the genomic DNA will be useful in studying disease processes at the level of the individual cell. It will be possible to isolated specific cell types based on their phenotypic characteristics and then determine their genetic and transcriptional signatures.