The RNA-binding protein SRSF3 has an essential role in megakaryocyte maturation and platelet production

Abstract

RNA processing is increasingly recognised as a critical control point in the regulation of different haematopoietic lineages including megakaryocytes responsible for the production of platelets. Platelets are anucleate cytoplasts that contain a rich repertoire of RNAs encoding proteins with essential platelet functions derived from the parent megakaryocyte. It is largely unknown how RNA binding proteins contribute to the development and functions of megakaryocytes and platelets. We show that Serine-arginine rich splicing factor 3 (SRSF3) is essential for megakaryocyte maturation and generation of functional platelets. Megakaryocyte-specific deletion of Srsf3 in mice led to macrothrombocytopenia characterised by megakaryocyte maturation arrest, dramatically reduced platelet counts and abnormally large functionally compromised platelets. SRSF3 deficient megakaryocytes failed to reprogram their transcriptome during maturation and to load platelets with RNAs required for normal platelet function. SRSF3 depletion led to nuclear accumulation of megakaryocyte mRNAs demonstrating that SRSF3 deploys similar RNA regulatory mechanisms in megakaryocytes as in other cell types. Our study further suggests that SRSF3 plays a role in sorting cytoplasmic megakaryocyte RNAs into platelets and demonstrates how SRSF3-mediated RNA processing forms a central part of megakaryocyte gene regulation. Understanding SRSF3 functions in megakaryocytes and platelets provides key insights into normal thrombopoiesis and platelet pathologies as SRSF3 RNA targets in megakaryocytes are associated with platelet diseases.

High ploidy large cytoplasmic megakaryocytes are hematopoietic stem cells regulators and essential for platelet production

“…Therefore, assessing LCM and SCM frequency, and not just ploidy or total MK numbers, should give more insight into thrombocytopenias. Furthermore, although analysis of platelet survival and function in MK-LCM Δ/Δ mice is beyond the scope of the current study, reduced platelet counts could also be, at least in part, explained by impaired survival, with platelets from these mice known to be cleared faster 30 .…”

“…In addition, we recently used RNA-sequencing analysis of MK isolated from MK-LCM Δ/Δ and MK-LCM WT/WT mice to demonstrate SRSF3 is critical during MK maturation 30 . Further analysis now reveals the serine/threonine protein kinase mTOR is significantly downregulated (2.3-fold) as WT 8N MK transition to 16N, but this significant decrease is absent in the transition of MK-LCM Δ/Δ 8N MK to 16N, with mTOR levels remaining unchanged and equivalent to WT 8N MK.…”

Sex differences in the associations of body size and body shape with platelets in the UK Biobank cohort

“…RNA processing is another mechanism controlling platelet formation. Deletion of the RNA-binding protein serine–arginine-rich splicing factor 3 (SRSF3) in mice results in arrest of megakaryocyte maturation, with sequestration of mRNAs in the megakaryocyte nucleus and production of a smaller number of dysfunction platelets with abnormally large size [ 57 ]. CRLF3 also plays a role in the maturation of proplatelets, with CRLF3 deficiency contributing to thrombocytopenia due to inefficient thrombopoiesis, with preplatelets, which are larger than the mature platelets, circulating for longer and being destroyed in the spleen before managing to mature into platelets [ 38 ].…”

Rbm8a deficiency causes hematopoietic defects by modulating Wnt/PCP signaling

“…We therefore hypothesize that, following Rbm8a perturbations, attenuated PCP through retention of mis-spliced mRNAs encoding non-canonical Wnt/PCP components affects migration or relative position of hematopoietic progenitors within the embryo as they migrate through signaling gradients. Notably, mice with defects in the EJC component Srsf3 also display thrombocytopenia 141 . The progressive recovery of the thrombocytopenia phenotype in TAR patients is compatible with an early defect in embryonic or fetal hematopoiesis when transient or intermediate progenitor waves are forming; the high plasticity and clonal expansion even of potentially reduced hematopoietic stem cells could subsequently replenish the diminished megakaryocyte levels during definitive hematopoiesis 1,2,25,[142][143][144][145] .…”