Orit Rozenblatt-Rosen et al in Nature:
Our knowledge of the cells that make up the human body, and how they vary from person to person, or throughout development and in health or disease, is still very limited. This week, a year after project planning began, more than 130 biologists, computational scientists, technologists and clinicians are reconvening in Rehovot, Israel, to kick the Human Cell Atlas initiative1 into full gear. This international collaboration between hundreds of scientists from dozens of universities and institutes — including the UK Wellcome Trust Sanger Institute, RIKEN in Japan, the Karolinska Institute in Stockholm and the Broad Institute of MIT and Harvard in Cambridge, Massachusetts — aims to create comprehensive reference maps of all human cells as a basis for research, diagnosis, monitoring and treatment. On behalf of the Human Cell Atlas organizing committee, we outline here some of the key challenges faced in building such an atlas — and our proposed strategies. For more details on how the atlas will be built as an open global resource, see the white paper2 posted on the Human Cell Atlas website. Cells have been characterized and classified with increasing precision since Robert Hooke first identified them under the microscope in the seventeenth century. But biologists have not yet determined all the molecular constituents of cells, nor have they established how all these constituents are associated with each other in tissues, systems and organs. As a result, there are many cell types we don’t know about. We also don’t know how all the cells in the body change from one state to another, which other cells they interact with or how they are altered during development.
New technologies offer an opportunity to build a systematic atlas at unprecedented resolution. These tools range from single-cell RNA sequencing to techniques for assessing a cell’s protein molecules and profiling the accessibility of the chromatin. For example, we can now determine the RNA profiles for millions of individual cells in parallel (see ‘From one to millions’). Protein composition and chromatin features can be studied in hundreds or thousands of individual cells, and mutations or other markers tracked to reconstruct cell lineages. We can also profile multiple variants of RNA and proteins in situ to map cells and their molecules to their locations in tissues.