Mapping cells to build a complete atlas of the human body

BODIES AREAAASDNARNADNADNARNA made of cells. Lots of them. An average adult human contains about 37.2trn cells, 100 times as many as the number of stars in the Milky Way. Clearly, trying to map the location of every one of these cells would be a futile endeavour. But cells are not identical. They are divided into many types, each specialised for different tasks. Mapping the location of each of these types is a more tractable problem. And that is the objective of the Human Cell Atlas project, a collaboration of researchers from 1,029 institutes in 71 countries around the world. Work on the atlas began in 2016, and its organisers hope to complete the effort by the end of this decade. Several of those involved gave a progress report to the meeting in Seattle.As Aviv Regev of the Massachusetts Institute of Technology explained, compiling the atlas has been made possible by a technique called single-cell transcriptome sequencing. This looks, a cell at a time, at the messenger molecules which carry instructions from a cell’s nucleus to the protein-making machinery in its cytoplasm. These messengers are made by transcribing genes into a -like chemical called . All an organism’s cells have more or less the same . What makes them different from each other is which bits of that are being actively transcribed, and thus what proteins are being made. This means identifying and counting the messengers shows what sort of cell it is.