This cellular atlas is a real “Google Maps of the human body”

This gigantic compendium, which describes a myriad of cell types in the human body, is the first concrete manifestation of the work that seeks to map our organism lengthwise, broadly, and crosswise.

As part of a massive collaborative effort spotted by ScienceAlert, a group of researchers has compiled a particularly impressive compendium that documents an incredible number of human cell types. With moreone million cell types mapped in 33 organsit’s about most comprehensive catalog of human cells to date.

These mapping efforts are carried out in parallel by lots of teams of researchers working in very different disciplines. Some dwell on protein diversity, or swear by the genome; those who produced this atlas are more particularly interested in the fundamental unit of life, namely the cell.

It is a generic term that can refer to lots of extremely different objects, both morphologically and functionally. All tissues in our body are made up of several specific cell populations; each of these types has its own internal machinery that directly defines its role in the fabric.

The Google Maps of the human body

Red blood cells, for example, specialize in transporting oxygen throughout the body. Neurons, for their part, are adapted to transport an electrical signal. And so on; beyond these well-known examples, there are tens of thousands of distinct types of cells, and each plays its own role.

Documenting all these cell types represents a major challenge in physiology, and by extension in clinical medicine; it is a question of better apprehending the diversity of living things in order to better understand its dynamics on a global scale. And to understand the architecture of this system and the way in which the different cells interact, we must already begin by knowing where they “live” in the body.

And that is precisely what a cohorte of more than 2300 researchers tried to do with these works which lasted several years. “We can see it as the Google maps of the human body”, summarizes Sarah Teichmann, geneticist at the Wellcome Sanger Institute and rapporteur of this work. “It’s really like a map of individual cells that shows where the positioning of each cell type in the target tissues.”

This is a particularly ambitious undertaking. Even though researchers have already been differentiating cell types for decades, it is simply unthinkable to identify them all manually under a microscope. To draw up this catalogue, the researchers therefore relied on a technology that is already revolutionizing the foundations of biotechnologies: machine learning.

Millions of needles, but a huge haystack

Until now, studies at the level of the individual cell have focused on genetic analysis of one tissue type at a time to map the cell types found there. An approach that is not only slow, but also complicated to use, because it is still necessary to ensure the overall consistency of each element thereafter.

As part of this work, the researchers developed several new analytical tools that allowed them to perform system-level analyses. They were thus able to verify precisely which cells express the genes, and under which conditions.

An excerpt from the Tabula Sapiens project, one of the components of the vast Human Cell Atlas. © Stephen R. Quake – Tabula Sapiens

Remember that technically, each cell in the body contains an (almost) exact copy of our genome. On the other hand, it does not use all of it. For each type of cell, only a part will be transcribed into proteins which take part in the biological activity: we speak of transcriptome.

People often think that the genome is the building block of the organism, but that’s not really correct”, nuance Steve Quake, bioengineer at Stanford. “The genome is more of a list of parts, and each cell uses a different set of parts”, he adds.

To distinguish all these types of cells, the researchers therefore chose to focus on their transcriptomes; an approach made possible by the rapid progress of associated technologies in recent years. Machine learning-based data processing systems then helped them sort through to produce their atlas.

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Clinical medicine is already benefiting from this work, and this is just the beginning. © Alexandr Podvalny – Pexels

A fundamental database for the medicine of tomorrow

It has already enabled substantial advances in biology. During this work, the researchers obviously identified new cell types that had never been documented before. But they also got their hands on new patterns of cellular communication, and even identified particularities that could play a central role in the evolution of certain diseases.

There is therefore reason to be enthusiastic for the rest of the operations. Because this first version of the Human Cell Atlas is only the beginning. Ultimately, the objective is of course to arrive at a completely exhaustive catalog of human cells. A goal that is still utopian today, but that is getting closer day by day.

The Human Cell Atlas is committed to including all variations of human cells, and is not intended to take a narrow view.”, explains Sarah Teichmann. And that’s good news. Because each time this catalog is expanded, research in basic biology will take a step forward.

And by extension, it will also allow for considerable clinical progress in all disciplines related to life sciences. A perspective that is already salivating pathologists, physiologists, geneticists, but also all other professionals who work directly or indirectly on human cells.

The studies that made it possible to build this atlas are available here, here, here, and here.

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