Project description:The Stem Cell Leukemia (Scl or Tal1) protein forms part of a multimeric transcription factor complex required for normal megakaryopoiesis. However, unlike other members of this complex such as Gata1, Fli1 and Runx1, mutations of Scl have not been observed as a cause of inherited thrombocytopenia. We postulated that functional redundancy with its closely related family member, Lymphoblastic Leukemia 1 (Lyl1) might explain this observation. To determine if Lyl1 can substitute for Scl in megakaryopoiesis, we examined the platelet phenotype of mice lacking one or both factors in megakaryocytes. Conditional Scl knockout mice crossed with transgenic mice expressing Cre recombinase under the control of the mouse platelet factor 4 (Pf4) promoter generated megakaryocytes with markedly reduced but not absent Scl. These Pf4SclcKO mice had mild thrombocytopenia and subtle defects in platelet aggregation. However, Pf4SclcKO mice generated on a Lyl1-null background (double knockout, DKO mice) had severe macrothrombocytopenia, abnormal megakaryocyte morphology, defective pro-platelet formation and markedly impaired platelet aggregation. DKO megakaryocytes, but not single knockouts, had reduced expression of Gata1, Fli1, Nfe2 and many other genes that cause inherited thrombocytopenia. These gene expression changes were significantly associated with shared Scl and Lyl1 E-box binding sites that were also enriched for Gata1, Ets and Runx1 motifs. Thus, Scl and Lyl1 share functional roles in platelet production and function by regulating expression of partner proteins including Gata1 and Fli1. We propose that this functional redundancy provides one explanation for the absence of Scl and Lyl1 mutations as a cause of inherited thrombocytopenia.
Project description:The SCL and LMO1 oncogenic transcription factors reprogram thymocytes into self-renewing pre-leukemic stem cells (pre-LSCs). Here we report that SCL directly interacts with LMO1 to activate the transcription of a self-renewal program coordinated by LYL1.
Project description:The bHLH transcription factor stem cell leukemia gene (Scl) is a master regulator for hematopoiesis essential for hematopoietic specification and proper differentiation of the erythroid and megakaryocyte lineages. However, the critical downstream targets of Scl remain undefined. Here, we identified a novel Scl target gene, transcription factor myocyte enhancer factor 2 C (Mef2C) from Sclfl/fl fetal liver progenitor cell lines. Analysis of Mef2C-/- embryos showed that Mef2C, in contrast to Scl, is not essential for specification into primitive or definitive hematopoietic lineages. However, adult VavCre+Mef2Cfl/fl mice exhibited platelet defects similar to those observed in Scl deficient mice. The platelet counts were reduced, while platelet size was increased and the platelet shape and granularity was altered. Furthermore, megakaryopoiesis was severely impaired in vitro. ChIP-on-chip analysis revealed that Mef2C is directly regulated by Scl in megakaryocytic cells, but not in erythroid cells. In addition, an Scl independent requirement for Mef2C in B-lymphoid homeostasis was observed in Mef2C-deficient mice, characterized as severe age-dependent reduction of specific B cell progenitor populations reminiscent of premature aging. In summary, this work identifies Mef2C as an integral member of hematopoietic transcription factors with distinct upstream regulatory mechanisms and functional requirements in megakaryocyte and B-lymphoid lineages.
Project description:The SCL and LMO1 oncogenic transcription factors reprogram thymocytes into self-renewing pre-leukemic stem cells (pre-LSCs). Here we report that SCL directly interacts with LMO1 to activate the transcription of a self-renewal program coordinated by LYL1. Gene expression profiles of thymocytes from SCL-LMO1 transgenic and age-matched non transgenic Cd3ε-/- mice were compared to identify candidate genes that confer self-renewal capability to pre-leukemic thymocytes.
Project description:Stem Cell Leukemia (Scl or Tal1) and Lymphoblastic Leukemia 1 (Lyl1) are highly related members of the basic helix-loop-helix (bHLH) family of transcription factors that are co- expressed in hematopoietic stem cells and the erythro-megakaryocytic lineages. Previous studies suggest that Scl is essential for hematopoietic development including primitive erythropoiesis. However, analysis of single-cell RNA-sequencing data of early embryos showed that primitive erythroid cells express both Scl and Lyl1. Therefore, to determine whether Lyl1 has a functional role in erythropoiesis, we crossed conditional Scl mice with transgenic mice expressing a Cre recombinase under the control of the Epo receptor, active in erythroid progenitors. Surprisingly, embryos with markedly reduced expression of Scl from E9.5 survived to adulthood. In contrast, mice with reduced expression of Scl and absence of Lyl1 (double knockout; DKO) died at E10.5 due to progressive loss of erythropoiesis. Consistent with a phenocopy of Gata1-null mice, gene expression profiling of DKO yolk sacs prior to the loss of erythrocytes (E9.5) revealed loss of Gata1 and many of the known target genes of the SCL-GATA1 complex. ChIP-seq analyses showed that LYL1 exclusively bound a small subset of SCL targets including GATA1. Together, these data show for the first time that Scl and Lyl1 share functional roles in primitive erythropoiesis.
Project description:Collagen is a potent agonist for platelet activation, presenting itself as a key contributor to coagulation via interactions with platelet glycoproteins. The fine-details dictating platelet-collagen interactions are poorly understood. In particular, glycosylation could be a key determinant in the platelet-collagen interaction. Here we report an affinity purification coupled to mass spectrometry-based approach to elucidate the function of N-glycans in dictating platelet-collagen interactions. By integrative proteomic and glycoproteomic analysis of collagen-platelet interactive proteins with N-glycan manipulation, we demonstrate that the interaction of platelet adhesive receptors with collagen are highly N-glycan regulated, with glycans on many receptors playing positive roles on collagen binding, with glycans on other platelet glycoproteins exhibiting inhibitory roles on the binding to collagen. Our results significantly enhance our understanding of the details of glycans influencing the platelet-collagen interaction.
Project description:Serine/arginine-rich (SR) proteins are important splicing factors which play significant roles in spliceosome assembly and splicing regulation. However, little is known regarding their biological functions in plants. Here, we analyzed the phenotypes of mutants upon depleting different subfamilies of Arabidopsis SR proteins. We found that loss of the functions of SC35 and SC35-like (SCL) proteins cause pleiotropic changes in plant morphology and development, including serrated leaves, late flowering, shorter roots and abnormal silique phyllotaxy. Using RNA-seq, we found that SC35 and SCL proteins play roles in the pre-mRNA splicing. Motif analysis revealed that SC35 and SCL proteins preferentially bind to a specific RNA sequence containing the AGAAGA motif. In addition, the transcriptions of a subset of genes are affected by the deletion of SC35 and SCL proteins which interact with NRPB4, a specific subunit of RNA polymerase II. The splicing of FLOWERING LOCUS C (FLC) intron1 and transcription of FLC were significantly regulated by SC35 and SCL proteins to control Arabidopsis flowering. Therefore, our findings provide mechanistic insight into the functions of plant SC35 and SCL proteins in the regulation of splicing and transcription to maintain the proper expression of genes and development.
Project description:Double anti-platelet therapy (DAPT) has wide inter-individual variabilities in coronary heart disease (CHD) patients’ responses, which undermines the prognosis effect in clinical practice. Noncoding RNAs are present in platelets, albeit their potential roles in platelet responses to DAPT largely remains in the realm of the unknown. This study aims to screen differential noncoding RNAs responsible for low residual platelet reactivities under DAPT. We enrolled 144 CHD patients that received DAPT and assigned them to high platelet reactivity (HPR) group and baseline group according to their residual platelet reactivities. Through microarray analysis, we detected a total of 22,424 kinds of co-expressed lncRNAs in three pairs of the patients between the HPR and baseline groups.