Megakaryocytopoiesis and Erythropoiesis
Project leader: Daphne Thijssen-Timmer PhD
Platelet assembly and release are the final events of a multi-step process involving commitment, proliferation and differentiation of hematopoietic stem cells (HSC) to megakaryocytes (MK). When MK differentiate from a bipotent megakaryocyte-erythroblast progenitor (MEP) they follow a distinct pathway. The so-called megakaryopoiesis starts with an increase in cytoplasm and endomitosis resulting in large polyploid cells, followed by proplatelet formation and finally shedding of platelets. Within Sanquin a robust human in vitro culture system for the generation of mature MK from hematopoietic stem (CD34+) cells has been developed over the past 10 years. However, a robust system for in vitro generation of human platelets from cultured megakaryocytes does not exist. Efforts are now made to optimize and extend our protocol towards in vitro generation of platelets and to this end we need a better understanding of the (transcription) factors that are specific for megakaryopoiesis and platelet release. We previously performed comparative transcriptome analysis on all mature blood cells (Watkins et al. 2009) and cultured erythroblasts and megakaryocytes (Macaulay et al. 2007) and found that the transcription factor MEIS1 was specifically expressed in MK, and we decided to study this transcription factor further.
The role of transcription factor MEIS1 in megakaryopoiesis
This research line focuses on the role of the transcription factor MEIS1 in human hematopoiesis. We previously developed a lentiviral system that allows us to over-express and knock-down MEIS1 in human hematopoietic stem and progenitor cells. Using this method, we discovered that expression of MEIS1 is indispensable for the megakaryocyte/erytroid lineage decision. We also showed that MEIS1 is a positive regulator of proliferation in megakaryocytes and erythrocytes (Zeddies et al.; manuscript in preparation). Since MEIS1 is specifically upregulated during megakaryopoiesis, we are currently studying which genes are regulated by MEIS1 and how these might affect platelet production and functionality. One of these genes is the RNA binding protein Ataxin-2 (ATXN2), which has an unknown role in hematopoiesis. We found that ATXN2 in megakaryocytes binds to proteins involved in translation initiation and mRNA storage and that knockdown of ATXN2 accelerates the megakaryocyte differentiation. We are currently studying the mechanisms by which ATXN2 affects the megakaryocyte differentiation.
- Zeddies S, De Cuyper IM, van der Meer PF, Daal BB, de Korte D, Gutiérrez L, Thijssen-Timmer DC. Pathogen reduction treatment using riboflavin and ultraviolet light impairs platelet reactivity toward specific agonists in vitro. Transfusion 2014 Apr 1. [Epub ahead of print]
- Macaulay IC, Tijssen MR, Thijssen-Timmer DC, Gusnanto A, Steward M, Burns P, Langford CF, Ellis PD, Dudbridge F, Zwaginga JJ, Watkins NA, van der Schoot CE, Ouwehand WH. Comparative gene expression profiling of in vitro differentiated megakaryocytes and erythroblasts identifies novel activatory and inhibitory platelet membrane proteins. Blood 2007; 109(8):3260-9.
- O’Conner MN, Thijssen-Timmer DC, Broos K, Deckmyn H. Platelet Proteomics, Chapter 11: Platelet Functional Genomics, Salles II, 12 July 2011, DOI: 10.1002/9780470940297. ch11.