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Developmental biology - Blood|
Creating blood stem cells from blood vessels
Reported in eLife, these findings could pave the way for further research into creating new blood cells for blood transfusions and in better understanding cancer development.
Blood vessels and blood cells develop from stem cells in the embryo. In fact, all blood stem cells responsible for the generation of all blood cell types, develop from the vascular cells which line the walls of blood vessels. This process happens in fish, birds and mammals, and is critical for the formation of blood.
However, how these vascular cells decide when to transform into blood stem cells was unknown. To understand the process of blood cell development the researchers studied seven transcription factors known to be important in blood cancers, using a powerful new technology called single cell transcriptomics. They discovered that in mouse embryo cells that are transitioning between vascular cells and blood cells, all seven of these factors are expressed at one time. However, when the team engineered various combinations of these transcription factors into embryonic stem cell lines (ESCs), used to model embryonic blood development in the petri dish, they discovered factors split unexpectedly into two distinct sets, one supporting the vascular cell fate and the other blood.
"This was the first time that anyone has been able to show how a group of transcription factors causes a vascular cell to choose to develop into a blood stem cell, and demonstrates the power of single-cell transcriptomics for characterising a really complex system of transcription factors. Using this technology, we could see the exact genes that were switched on in every single cell, and found that the transcription factors acted as a fork in the road of development of blood cells."
The study was highly technically challenging. Not only was it difficult to express so many transcription factors simultaneously in ESCs, it was also the first time that single-cell transcriptomics had been used to study a large complex of transcription factors.
Dr Tallulah Andrews, joint second author on the paper from the Wellcome Sanger Institute: "This was a very challenging computational problem as there was a huge network of interactions in the complex that needed to be unravelled. By applying recent advances in statistics to this biological question, we were able to predict that some of the transcription factors were acting in opposition to each other like a switch, rather than working together, which the study was then able to prove experimentally."
The knowledge gained in the study could aid further research towards the creation of blood stem cells for use in transfusions or blood cancer treatments, and could also help in the understanding of metastasis, which is when cancer cells spread to other organs.
Dr Christophe Lancrin, a corresponding author on the paper from the European Molecular Biology Laboratory, Rome, adds:"We have revealed the gene regulatory network responsible for switching off the vascular cell fate and switching on the blood program to generate blood stem cells. Interestingly, the process of metastasis in cancer also involves changes in cell states and may use a similar process to the one we have discovered. If we could better understand how the transcription factors responsible for different cell states compete with each other we could begin to think of ways to specifically inhibit this process and improve the chance of survival of cancer patients."
Recent advances in single-cell transcriptomics techniques have opened the door to the study of gene regulatory networks (GRNs) at the single-cell level. Here, we studied the GRNs controlling the emergence of hematopoietic stem and progenitor cells from mouse embryonic endothelium using a combination of single-cell transcriptome assays. We found that a heptad of transcription factors (Runx1, Gata2, Tal1, Fli1, Lyl1, Erg and Lmo2) is specifically co-expressed in an intermediate population expressing both endothelial and hematopoietic markers. Within the heptad, we identified two sets of factors of opposing functions: one (Erg/Fli1) promoting the endothelial cell fate, the other (Runx1/Gata2) promoting the hematopoietic fate. Surprisingly, our data suggest that even though Fli1 initially supports the endothelial cell fate, it acquires a pro-hematopoietic role when co-expressed with Runx1. This work demonstrates the power of single-cell RNA-sequencing for characterizing complex transcription factor dynamics.
Authors: Isabelle Bergiers Tallulah Andrews Özge Vargel Bölükba?? Andreas Buness Ewa Janosz Natalia Lopez-Anguita Kerstin Ganter Kinga Kosim Cemre Celen Gülce It?r Perçin Paul Collier Bianka Baying Vladimir Benes Martin Hemberg Is a corresponding author Christophe Lancrin.
European Molecular Biology Laboratory (EMBL)
EMBL is Europe's flagship laboratory for the life sciences. Established in 1974 as an intergovernmental organisation, EMBL is supported by over 20 member states. EMBL performs fundamental research in molecular biology, studying the story of life. The institute offers services to the scientific community; trains the next generation of scientists and strives to integrate the life sciences across Europe. EMBL is international, innovative and interdisciplinary. Its more than 1600 staff, from over 80 countries, operate across six sites in Barcelona (Spain), Grenoble (France), Hamburg (Germany), Heidelberg (Germany), Hinxton (UK) and Rome (Italy). EMBL scientists work in independent groups and conduct research and offer services in all areas of molecular biology. EMBL research drives the development of new technology and methods in the life sciences. The institute works to transfer this knowledge for the benefit of society. https://www.embl.de/
Wellcome Sanger Institute
The Wellcome Sanger Institute is one of the world's leading genome centres. Through its ability to conduct research at scale, it is able to engage in bold and long-term exploratory projects that are designed to influence and empower medical science globally. Institute research findings, generated through its own research programmes and through its leading role in international consortia, are being used to develop new diagnostics and treatments for human disease. To celebrate its 25th year in 2018, the Institute is sequencing 25 new genomes of species in the UK. Find out more at http://www.sanger.ac.uk or follow @sangerinstitute
Wellcome exists to improve health for everyone by helping great ideas to thrive. We're a global charitable foundation, both politically and financially independent. We support scientists and researchers, take on big problems, fuel imaginations and spark debate. http://www.wellcome.ac.uk
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Diagram of how HSC cells are formed during embryonic period from endothelial cells the building blocks of the vascular system responsible for blood circulation throughout the body. This process is called endothelial to hematopoietic transition (EHT). EHT is dependent on the activity of transcription factor RUNX1, a master regulator of blood development. Image: Lancrin Group EMBL Rome, Italy.