In the mid-seventeenth century, Robert Hooke, an English microscopist, had a question that, although apparently simple or banal, led to the "discovery" of the basic component of all living things.The question that kept Hooke up all night, as Gerald Karp recalls in his book Cellular and Molecular Biology, was why corks were used to keep the air inside wine bottles.One day, to solve it, Hooke took a knife, cut the cork made from cork oak bark and examined it under one of the microscopes he had made."I seemed to perceive that it had a porous appearance much like a honeycomb," he wrote.Those pores, which he called "cells," actually corresponded to "empty walls of dead tissue, walls that were originally produced by the living cells that surrounded it," says Karp.That is, Hooke first observed and described cells.Last week, four centuries after that first observation, a consortium of scientists published the most comprehensive Human Cell Atlas (HCA) to date.They presented him with three investigations published in the most recent edition of the journal Science.The consortium that coordinated this work was created in 2016 with one goal: "Mapping all types of cells in the human body, both to understand human health and to diagnose, monitor and treat diseases," says Dr. Cecilia Domínguez Conde to El Viewer.Conde is the lead author of one of those articles and she works at the Wellcome Sanger Institute, one of the co-founders of the HCA.There she is a member of the Teichmann Group, where she is doing her postdoctoral stay, while leading Human Technopole, a medical research institute located in Milan.In summary, the works analyzed more than a million cells, one by one, from 33 organs and identified 500 different cell types, offering detailed maps of their functions.“It is a milestone for the HCA.These data provide new biological insights into human health and disease.They also represent a great advance in understanding the development and structure of the immune system”, comments Conde.But what does this atlas mean?How did science get to this point?And, what is needed then? These are some of the questions that must be resolved.To understand the first, it is necessary to go back to some basic principles of biology: DNA, messenger RNA, proteins and cells.Ricardo Peña, professor of medicine at the Universidad de los Andes and doctor of pharmacology, has a metaphor that can help to better understand the subject without having to go back to school biology texts.Imagine, he points out, that DNA is a big "book" with 21,000 recipes, which is the number of genes that human beings have.A copy of these recipes would be messenger RNA, and the people who would use that information would represent the cells.The final dish they would prepare would be protein.Now, since two people would surely not use the same recipes, they would end up preparing different dishes.DNA contains the genetic information of every human being.This DNA is identical for all cells.But then why are cells different and perform different functions?Basically because, just like the people in the metaphor, each cell reads different genes from the DNA book to make its proteins.For a long time, Peña says, the only way to differentiate cells was through what we saw through microscopes.But this was reduced to the visual plane.The problem, he continues, is that in this way some cells could look very similar even though they fulfilled different functions."The only way to understand their possible differences is to understand how they read DNA, what messenger RNAs they made, and what proteins they're making," he says.Fortunately, this is a process that has been possible for two decades, thanks to advances in transcriptomics, the study that measures all the messenger RNAs in a sample, that is, it looks at the recipes that are being used by the cells. .The three studies used this technique with an additional ingredient: they sequenced cell by cell, a technique known as “single cell”, something that was not possible a few years ago.In addition, Peña acknowledges, one of the advantages of these works was having used samples from different organs or tissues from the same person, "which ensures that the samples were exposed to the same conditions."For Marcela Camacho, doctor and professor of biology at the National University, one of the main contributions of these works is that "the complexity of cell differentiation is much greater than we thought."In other words, the visual stage that Peña was talking about has been overcome.Now, although a group of cells look similar, it is possible to know precisely that they are not the same and, thanks to their messenger RNA, it is possible to infer what type of function they are going to fulfill.“Before we assumed that a muscle cell was the same everywhere.Perhaps we thought it was bigger in larger muscles.Now we know that the cells between muscles are not the same.And that, even, they are different in the different zones of that muscle”, exemplifies Camacho.And she points out that one of the great uses that this information will have has to do with precision medicine.“A few years ago we had to see a gigantic cancer to be able to detect it.Then certain diagnostic measures were generated that allowed us to identify a tiny cancer in a tissue.Right now, with this technique, you can detect a single cancer cell."“Our work on immunology also allows us to make a great leap forward in our understanding of the development and structure of the immune system in tissues.This could serve as a framework for the development of therapies to fight diseases related to the immune system”, adds Conde by mail.So what is missing?The short answer is that there is still a long way to go.The long term, according to Gloria Patricia Cardona, full professor at the Antioquia University School of Medicine and coordinator of the cellular and molecular neurobiology area of ​​the neuroscience group, includes contemplating that each human being, according to some calculations, has approximately 72 billion cells."That's 100 times the number of stars the Milky Way has," she adds.That is why he comments that, in his opinion, this is a project that is going to be fed, it is going to be putting information that will add pieces to the puzzle each time to have closer information on how our cells work and how we can help them maintain a healthy state”.For her part, Conde points out that the HCA hopes to complete this first draft by next year or by 2024. A mature atlas will not arrive within a decade.Along the same lines, Cardona points out that "in a certain sense the Atlas will always be in development."Because each human individual is unique, the Human Cell Atlas will be continually updated as more data become available and our understanding of the human body continues to expand, well into the future.”Meanwhile, Patricia Severino, a researcher at the Instituto Israelita de Ensino e Pesquisa-Hospital Israelita Albert Einstein, in Sao Paulo (Brazil) told El Espectador that, within the framework of the HCA consortium, researchers from Brazil, Chile, Colombia, Mexico and Peru, "are engaged in a joint project that aims to bring together a first Latin American cellular map of immune blood cells and gallbladder tissue from various indigenous and mixed populations throughout the Americas."While the research progresses and the Human Cell Atlas is adding pieces, Dr. Camacho reflects on the findings of the three works and points out that, ultimately, what they have achieved is to demonstrate that the unit of singularity "is no longer even the individual .It's the cell."