Objective The immune system is a complex ensemble of diverse lineages. Studies on in-vivo-hematopoiesis have untilnow largely rested on transplantation. More physiological experiments have been limited by the inability toanalyze hematopoietic stem (HSC) and progenitor cells in situ without cell isolation and other disruptivemanipulations. We have developed mouse mutants in which a fluorescent marker can be switched on in HSCin situ (inducible fate mapping), and traced HSC lineage output under unperturbed conditions in vivo. Theseexperiments uncovered marked differences comparing in situ and post-transplantation hematopoiesis. Thesenew developments raise several important questions, notably on the developmental fates HSC realize in vivo(as opposed to their experimental potential), and on the structure (routes and nodes) of hematopoiesis fromHSC to peripheral blood and immune lineages. Answers to these questions (and in fact the deconvolution ofany tissue) require the development of non-invasive, high resolution barcoding systems. We have nowdesigned, built and tested a DNA-based barcoding system, termed Polylox, that is based on an artificialrecombination locus in which Cre recombinase can generate several hundred thousand genetic tags in mice.We chose the Cre-loxP system to link high resolution barcoding (i.e. the ability to barcode single cells and tofate map their progeny) to the zoo of tissue- or stage-specific, inducible Cre-driver mice. Here, I will presentthe principles of this endogenous barcoding system, demonstrate its experimental and analytical feasibilitiesand its power to resolve complex lineages. The work program addresses in a comprehensive manner majoropen questions on the structure of the hematopoietic system that builds and maintains the immune system.This project ultimately aims at an in depth dissection of unique or common lineage pathways emerging fromHSC, and at resolving relationships within cell lineages of the immune system. Fields of science medical and health sciencesbasic medicineimmunologymedical and health sciencesclinical medicinetransplantation Keywords LoxP Cre recombinase-driven barcoding hematopoiesis hematopoietic stem and progenitor cells high resolution in vivo fate mapping leukocyte development maintenance of the blood and immune system Programme(s) H2020-EU.1.1. - EXCELLENT SCIENCE - European Research Council (ERC) Main Programme Topic(s) ERC-2016-ADG - ERC Advanced Grant Call for proposal ERC-2016-ADG See other projects for this call Funding Scheme ERC-ADG - Advanced Grant Host institution DEUTSCHES KREBSFORSCHUNGSZENTRUM HEIDELBERG Net EU contribution € 2 500 000,00 Address IM NEUENHEIMER FELD 280 69120 Heidelberg Germany See on map Region Baden-Württemberg Karlsruhe Heidelberg, Stadtkreis Activity type Research Organisations Links Contact the organisation Opens in new window Website Opens in new window Participation in EU R&I programmes Opens in new window HORIZON collaboration network Opens in new window Total cost € 2 500 000,00 Beneficiaries (1) Sort alphabetically Sort by Net EU contribution Expand all Collapse all DEUTSCHES KREBSFORSCHUNGSZENTRUM HEIDELBERG Germany Net EU contribution € 2 500 000,00 Address IM NEUENHEIMER FELD 280 69120 Heidelberg See on map Region Baden-Württemberg Karlsruhe Heidelberg, Stadtkreis Activity type Research Organisations Links Contact the organisation Opens in new window Website Opens in new window Participation in EU R&I programmes Opens in new window HORIZON collaboration network Opens in new window Total cost € 2 500 000,00