Sequencing one cell at a time

Whether DNA comes from a neuron or a liver cell, it contains all the genetic information needed to create every other cell in the body. The difference between these cells isn’t their DNA; it’s how they use it. Activating the right genes at the right time triggers a biochemical cascade that gives each cell the tools it needs to play its role in the body. Each time a gene is read, or transcribed, the cell produces a molecule of messenger RNA, creating a marker for which genes are active in a cell. This pattern of activity varies between cell types and at different stages in their development.

Identifying these different RNA transcripts through sequencing offers a window into the inner workings of the cell. Gathering enough RNA material to analyse, however, has typically required studying bulk samples of thousands of seemingly identical cells. This approach is akin to examining the contents of a fruit smoothie; we can identify all of the molecules that are present, but we have lost the information on which fruit they came from originally and how those fruits differ.