Seminar Details

Evolutionary origin of the mammalian hematopoietic and immune systems found in a colonial chordate




Dr. Benyamin Rosental - Institute for Agriculture and Biotechnology, Ben Gurion University of the Negev


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. By means of flow-cytometry in combination with screened antibodies by Cytof, lectins, and fluorescent enzymatic reagents, we isolated 34 B. schlosseri cell populations. Using whole-transcriptome sequencing of defined cell populations, and diverse functional assays, we identified HSCs, progenitors, immune-effector cells, and the HSC niche. 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. Furthermore, we identified a B. schlosseri cytotoxic cell population originating from large granular lymphocyte-like cells and demonstrated that self-recognition inhibits cytotoxic reaction.

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