[Exploring the mysteries of megakaryocytopoiesis and thrombopoiesis through comparative hematology]

In modern hematology, research on hematopoiesis and blood cells in vertebrates, such as birds, reptiles, amphibians, and fish, is lagging. This is because there are many experimental constraints when selecting subjects other than humans and mice as research subjects. Currently, the availability of flow cytometry to count classified nucleated blood cells and utilization of whole genome information have led to novel findings. For example, in case of amphibian hematopoiesis studies, megakaryocytes have been found to be present in African clawed frogs (Xenopus laevis), which do not have platelets but have circulating nucleated thrombocytes. Moreover, we shed light on several mysteries, such as the C-terminal region in human TPO molecules not being found in birds, amphibians, and fish TPO molecules and the functional universalities of mutant CALR-MPL binding and EPO-EphB4 binding, in conjunction with comparative hematology.