@article {Rosental206318, author = {Benyamin Rosental and Mark Kowarsky and Jun Seita and Daniel M. Corey and Katherine J. Ishizuka and Karla J. Palmeri and Shih-Yu Chen and Rahul Sinha and Jennifer Okamoto and Gary Mantalas and Lucia Manni and Tal Raveh and D. Nathaniel Clarke and Aaron M. Newman and Norma F. Neff and Garry P. Nolan and Stephen R. Quake and Irving L. Weissman and Ayelet Voskoboynik}, title = {Evolutionary Origin of the Mammalian Hematopoietic System Found in a Colonial Chordate}, elocation-id = {206318}, year = {2017}, doi = {10.1101/206318}, publisher = {Cold Spring Harbor Laboratory}, abstract = {Hematopoiesis is an essential process that evolved in multicellular animals. At the heart of this process are hematopoietic stem cells (HSCs), which are multipotent, self-renewing and generate the entire repertoire of blood and immune cells throughout life. Here we studied the hematopoietic system of Botryllus schlosseri, a colonial tunicate that has vasculature, circulating blood cells, and interesting characteristics of stem cell biology and immunity. Self-recognition between genetically compatible B. schlosseri colonies leads to the formation of natural parabionts with shared circulation, whereas incompatible colonies reject each other. Using flow-cytometry, whole-transcriptome sequencing of defined cell populations, and diverse functional assays, we identified HSCs, progenitors, immune-effector cells, the HSC niche, and demonstrated that self-recognition inhibits cytotoxic reaction. Our study implies that the HSC and myeloid lineages emerged in a common ancestor of tunicates and vertebrates and suggests that hematopoietic bone marrow and the B. schlosseri endostyle niche evolved from the same origin.}, URL = {https://www.biorxiv.org/content/early/2017/12/26/206318}, eprint = {https://www.biorxiv.org/content/early/2017/12/26/206318.full.pdf}, journal = {bioRxiv} }