Thrombopoietin induces production of nucleated thrombocytes from liver cells in Xenopus laevis

Abstract

The development of mammalian megakaryocytes (MKs) and platelets, which are thought to be absent in non-mammals, is primarily regulated by the thrombopoietin (TPO)/Mpl system. Although non-mammals possess nucleated thrombocytes instead of platelets, the features of nucleated thrombocyte progenitors remain to be clarified. Here, we provide the general features of TPO using Xenopus laevis TPO (xlTPO). Platelets are generated from the cytoplasm of polyploid megakaryocytes (MKs). In humans, MKs differentiate from haematopoietic stem cells (HSCs) and constitute only a small fraction of bone marrow cells (0.1%-0.5%) 1 . MKs are unique cells that undergo DNA replication, giving rise to polyploid cells that undergo proplatelet formation 2 . The proliferation and maturation of MKs by thrombopoietin (TPO), a ligand for the receptor encoded by the c-mpl proto-oncogene (Mpl) 3-5 , has been well characterized. TPO has been independently identified and purified from different species in mammals 6,7 . In contrast, the origin and development of circulating nucleated thrombocytes in most non-mammalian vertebrates, including fish 8-10 , amphibians 11 , reptiles 12 and aves 13 , remain unknown 14,15 . The evolutionary advantage of deriving platelets from MKs has been previously discussed 16 . Circulating thrombocytes mediate haemostasis and blood coagulation, and result in the activation and cytoskeletal changes of non-mammalian nucleated thrombocytes, similar to those of platelets 17 . In zebrafish, thrombin activates nucleated thrombocytes produced by TPO stimulation 18 . Nevertheless, it is not clear whether polyploid MKs are the precursors of mature nucleate thrombocytes.In humans, HSCs develop into committed multipotent progenitors, which in turn differentiate to produce lymphocyte progenitors, granulocyte/monocyte progenitors, and MK/erythroid progenitors (MEPs). MEPs committed to the formation of erythroid and megakaryocytic progeny then produce mature erythrocytes or platelets 19 . Although TPO is one of the most important inducers of MK maturation, high concentrations of TPO inhibit proplatelet formation in vitro 20 . Recently, Nishimura et al. reported that the IL-1α also stimulates platelet production in response to acute platelet needs 21 . Newly released peripheral platelets exhibit bipolar morphology of round cells and multi-bodied proplatelets 22 . Proplatelet formation and platelet release are accelerated by shear forces in vitro 23 .

The role of the red blood cell and platelet in the evolution of mammalian and avian endothermy

“…The model, unlike the mammalian model, depicts the formation of a polymerizing fibrin clot as the first step in repairing a vessel wall injury (b(iii)) followed by the binding of thrombocytes to collagen and a hard clot-forming with some cross-linking of thrombocytes and trapping of RBCs within the clot (b(iii,iv)) SOSLAU | 123 dearth of knowledge about their role in hemostasis and responses to platelet agonists. The progenitor cell for nonmammalian RBCs and thrombocytes is a bipotential thrombocytic/erythroid progenitor cell (TEPs) derived from self-renewing hematopoietic stem cells (HSCs; Svoboda & Bartunek, 2015;Svoboda et al, 2014;Tanizaki et al, 2015) in a sequence akin to the mammalian system that ultimately yields RBCs and megakaryocytes from the bipotential megakaryocyte/ erythroid progenitor cell (MEPs; Svoboda & Bartunek, 2015;Wong, Dolinska, Sigvardsson, Ekblom & Qian, 2016;Woolthuis & Park, 2016;Xavier-Ferrucio & Krause, 2018). Some evidence indicates that the mammalian bipotential MEP cell and its progeny cells, RBCs, and megakaryocytes, may also arise from alternate pathways (Woolthuis & Park, 2016;Xavier-Ferrucio & Krause, 2018).…”

“…Some evidence indicates that the mammalian bipotential MEP cell and its progeny cells, RBCs, and megakaryocytes, may also arise from alternate pathways (Woolthuis & Park, 2016;Xavier-Ferrucio & Krause, 2018). The ultimate production of RBCs and thrombocytes/platelets in both nonmammalian and mammalian systems is dictated by levels of TPO (thrombopoietin) and EPO (erythropoietin) that bind to analogous receptors stimulating similar signaling pathways in both cell types (Svoboda & Bartunek, 2015;Svoboda et al, 2014;Tanizaki et al, 2015;Woolthuis & Park, 2016;Xavier-Ferrucio & Krause, 2018). In fact, it is proposed that TPO and EPO and their respective receptors evolved from single genes that underwent duplication during evolution (Svoboda & Bartunek, 2015).…”

Amphibian thrombocyte‐derived extracellular vesicles, including microRNAs, induce angiogenesis‐related genes in endothelial cells

“…However, thrombocytes exist in circulating blood in zebrafish (Jagadeeswaran et al., 1999), bullfrogs (de Abreu Manso et al., 2009), X . laevis (Tanizaki et al., 2015) and birds (Ody et al., 1999); thus, a high level of expression in the peripheral blood was thought to be reasonable. The spleen also exhibited high levels of cd41 expression.…”

Flow cytometric analysis of Xenopus laevis and X. tropicalis blood cells using acridine orange

“…Although this method is easy to use with Shaw’s diluent solution, supravital stain 2 , or Natt and Herrick solution 10 , it remains difficult to distinguish between activated thrombocytes and lymphocytes. To develop an automated classification and counting system, we used X. laevis and X. tropicalis as animal models, since they possess nucleated blood cell types including erythrocytes, leukocytes, and thrombocytes, as well as their unclassified progenitors 2 , 11 , 12 . Additionally, using the T12 monoclonal antibody targeting X. laevis thrombocytes 13 , we were able to distinguish X. laevis thrombocytes from other types of blood cells.…”