Megakaryocytes are large cells that play an important role in haemostasis through the production of platelets, which are critical for clotting. Despite their importance, in vitro production of megakaryocytes and platelets are limited, and the main supply of platelets still relies on plasma donations.
In the mouse bone marrow, megakaryocytes (MK) mature from haematopoietic stem cells (HSCs) via three pathways. The first pathway follows a traditional hierarchical pathway where HSCs differentiate into multipotent progenitors (MPP), then common myeloid progenitors (CMP), followed by megakaryocyte-erythroid progenitors (MEP), to MK progenitors (MkP), and ultimately into mature MKs. In the second pathway, HSCs differentiate into a specific subset of MPP (MPP2) which then differentiates into MkPs. Finally, in the last pathway, certain long-term HSCs (LT-HSC) differentiate into MkPs. Recently, single cell sequencing of MKs have revealed different subsets of MK subpopulations (Sun et al. Blood 2021). This finding suggests the possibility that in vitro production of MKs might not reflect the full breadth of MK diversity and curtail the production of platelet producing cells. To test this, we are comparing in vitro and in vivo MK emergence using single cell RNA sequencing.
Using flow cytometry, all populations known to be involved in megakaryocyte formation were isolated and sequenced. Within our dataset, we have found subpopulations of megakaryocytes, confirming their diversity, and identified potential transcriptional trajectories. We are in the process of maturing HSCs, MPPs, and MkPs into MKs in vitro. By comparing these two systems, we will assess how in vitro MK production compares to their in vivo emergence and improve MK - and ultimately platelet - production.