1 SCIENTIFIC REPORTS | 6:27379 | DOI: 10.1038/srep27379 www.nature.com/scientificreports Heterogeneous Nuclear Ribonucleoprotein L is required for the survival and functional integrity of murine hematopoietic stem cells Marie-Claude Gaudreau 1,2,* , Damien Grapton 1,2,* , Anne Helness 1,3,* , Charles Vadnais 1,2 , Jennifer Fraszczak 1,2 , Peiman Shooshtarizadeh 1 , Brian Wilhelm 4 , François Robert 1,5 , Florian Heyd 6 & Tarik Möröy 1,2 The proliferation and survival of hematopoietic stem cells (HSCs) has to be strictly coordinated to ensure the timely production of all blood cells. Here we report that the splice factor and RNA binding protein hnRNP L (heterogeneous nuclear ribonucleoprotein L) is required for hematopoiesis, since its genetic ablation in mice reduces almost all blood cell lineages and causes premature death of the animals. In agreement with this, we observed that hnRNP L deficient HSCs lack both the ability to self- renew and foster hematopoietic differentiation in transplanted hosts. They also display mitochondrial dysfunction, elevated levels of γH2AX, are Annexin V positive and incorporate propidium iodide indicating that they undergo cell death. Lin - c-Kit + fetal liver cells from hnRNP L deficient mice show high p53 protein levels and up-regulation of p53 target genes. In addition, cells lacking hnRNP L up- regulated the expression of the death receptors TrailR2 and CD95/Fas and show Caspase-3, Caspase-8 and Parp cleavage. Treatment with the pan-caspase inhibitor Z-VAD-fmk, but not the deletion of p53, restored cell survival in hnRNP L deficient cells. Our data suggest that hnRNP L is critical for the survival and functional integrity of HSCs by restricting the activation of caspase-dependent death receptor pathways. In mice, hematopoiesis originates from hematopoietic stem cells (HSC) that migrate from the aorta-gonad-mesonephros region (AGM) towards the fetal liver (FL) at embryonal stage 10.5 day post-coitus and later on, takes place in the bone marrow (BM) of adult mice 1,2 . In both FL and BM, HSCs possess a unique self-renewal capacity and the potential to generate all mature blood and immune cells of an organism throughout its lifetime 3–5 . e commitment of HSCs to differentiate into specific cell lineages is tightly regulated and starts with the formation of multipotent progenitors (MPPs) that have a reduced self-renewal capacity and are already restricted in their multilineage potential 6,7 . e earliest precursors that emerge from MPPs still have both myeloid and lymphoid potential and are called LMPPs 8,9 . HSCs reside in the BM or the FL and are part of the Lin − Sca1 + cKit + (LSK) subset. ey can be further defined by the expression of the markers CD150 and CD48 (i.e. HSCs are Lin − Sca1 + cKit + CD150 + CD48 − ) 10–13 . While most HSCs in adult mice are in a quiescent stage, embryonic HSCs are proliferating to generate the adult pool of stem cells 5,14,15 . Many transcription factors including Runx1, Gfi1, Gfi1b, GATA2, SCL and Notch1 have been identified as important regulators of lineage commitment as well as HSCs quiescence and survival 16–20 . However, the role that mRNA processing factors may have for HSCs remains unexplored, even though they are known to control gene expression at the transcriptional and posttranscriptional level 21,22 . 1 Institut de recherches cliniques de Montréal (IRCM) 110 Avenue des Pins, Montréal, QC H2W 1R7, Canada. 2 Département de microbiologie, infectiologie et immunologie, Université de Montréal, C.P. 6128, succ. Centre- ville, Montréal, H3C 3J7, Canada. 3 Department of Experimental Medicine, McGill University, 1110 Pins Avenue West Room 101, Montréal, Quebec, H3A 1A3, Canada. 4 Institut de recherche en immunologie et cancerologie (IRIC), Université de Montréal, 2950 Chemin de Polytechnique, Marcelle-Coutu Pavilion, Montréal, Quebec, H3T 1J4, Canada. 5 Département de médecine, Faculté de médecine, Université de Montréal, Montréal, Canada. 6 Institut für Chemie und Biochemie, Freie Universität Berlin, Berlin, Germany. * These authors contributed equally to this work. Correspondence and requests for materials should be addressed to T.M. (email: Tarik.Moroy@ircm.qc.ca) Received: 11 August 2015 Accepted: 16 May 2016 Published: 07 June 2016 OPEN