I am a thrombocyte also known as the platelet and I am found in the Peripheral Blood of the zebrafish. I originated from cells known as megakaryocytes, which are found predominantly in the bone marrow. My major purpose in the zebrafish is hemostasis which it is a defence mechanism that controls blood clotting in the event of an injury.
There are two main steps in hemostasis: primary hemostasis where the platelets aggregate and plug the wound and then secondary hemostasis which results in the formation of fibrin clots.
The megakaryocytes originated from stem cells called pluripotent hematopoietic stem cells. These stem cells undergo differentiation in the bone marrow to become a megakaryoblast and eventually into a megakaryocyte. The main regulator involved in the formation of the megakaryocyte is thrombopoietin or TPO.
Other molecular signals have been associated with the formation of the megakaryocyte such as IL-3, IL-6 and IL-11.
Before the megakaryotes are able to release platelets the cell is enlarged by endomitosis. During this process the DNA is expanded and there is also the formation of internal membrane systems, granules, and organelles as well the demarcation membrane system (DMS).
Zebrafish thrombocytes a sparse cytoplasm with large nuclei. The cytoplasm contains many vesicles that open to the cell surface.