NAfter the entire genome, researchers map all human cells. For this atlas of human cells, the three teams have now analyzed more than 500 cell types in 33 tissues in one big step and condensed them into rough maps. The teams present their work in the journal “Science”. Another team analyzed cells from embryos.
With the atlas of human cells, it is possible to see in which tissues there are doors for corona or flu viruses, says study leader Sarah Teichmann from the British Wellcome Sanger Institute. She is the co-founder of the Human Cell Atlas (HCA) project, which started in 2016 and involves more than 2000 researchers worldwide.
“Atlas tells us which cells have open doors for which viruses. In March, we saw that there are receptors for Covid-19 in the nose, and the study was published in April 2020.” It showed how important masks are.
The atlas shows where the receptors are located
In addition, her team showed that corona viruses also penetrate certain cells of the lining of the mouth and are therefore expelled when they speak. “The cell atlas is like a guide that shows which receptor is in which position.” This is not only important for viruses, but also for drug development.
Work on the cell atlas has been going on for years, but so far mostly individual cells, tissues or organs have been cataloged, explains Teichmann, who is also director of research at the British University of Cambridge. The cell maps presented in “Science” can be used to show how cells work together in different organs.
“In the immune system, we have now learned which T cells are present in which tissues, and so we have created a kind of GPS,” says Teichmann. T cells form different receptors in the spleen than in other organs. In addition, analysis techniques have been significantly improved. “We’re at a point where the technologies are very robust, fast and affordable.”
This is not only important for finding receptors. “The healthy tissue stored in the atlas is primarily used as a reference for diseases. It’s easy to see what has changed in the patient,” said Teichmann.
Just as the Human Genome Project provides a reference for all genes, the human cell atlas is a reference for all cells, said the project’s co-founder, Aviv Regev of the Broad Institute in Cambridge, Massachusetts. This alone is a lot more data.
All cells of the human body have the same genome, but use different parts of it. “It is not enough to identify disease genes, you also need to know where they are active.” The atlas, which is publicly available to researchers, can also be used to identify disease-causing cells.
Analysis of mRNA is crucial
Another team from Teichmann examined the embryonic immune system in the fourth “Science” paper for the Cell Atlas and proved that immune cells develop in many organs, not just hematopoietic ones. “Examining cells and tissues at stages of human development helps us, among other things, to understand rare diseases that often appear at birth and the origin of tumors in children, which often develop during pregnancy,” explains Teichmann.
Before this work, about 100 individual studies analyzing tissues from many people had already contributed to the cell atlas. A team led by Roland Eils from Berlin’s Charité has already mapped the pancreas in 2020 – genetically examining all the cells in it, determining their exact location and elucidating the connections between individual cells.
“We wanted to create a resource for all researchers who are interested in the pancreas,” Eils explained at the time. Norbert Hübner of the Max Delbrück Center for Molecular Medicine in Berlin was responsible for the initial sketch of the heart.
For the cell atlas, researchers analyze the small working copies (mRNA) of the genome, which are necessary as instructions for the production of desired substances in the cell. However, in the meantime, it is also possible to examine frozen tissue using only cell nuclei. The cell atlas is not yet complete. “Actually, we wanted the first draft to be ready within five years,” Teichmann said. But the pandemic got in the way. One end is open.
“We don’t even know how many cell types people have,” Teichmann admits, though there are more than previously thought. “The body has over 50 tissues. Taken together, we now have a rough draft map with 30 tissues and 50 million individual cells,” said Teichmann. “This is a very good start. However, the brain is still missing.” Only small parts have been mapped, and there are about 100 areas of the human brain.