Megakaryocytes Regulate Hematopoietic Stem Cell Quiescence through CXCL4 Secretion Researchers show that megakaryocytes (MKs) can directly regulate hematopoietic stem cell (HSC) pool size in mice. Three-dimensional whole-mount imaging revealed that endogenous HSCs are frequently located adjacent to MKs in a nonrandom fashion. [Nat Med] Abstract Myeloproliferative Neoplasms Can Be Initiated from a Single Hematopoietic Stem Cell Expressing JAK2-V617F Researchers demonstrate by limiting dilution and single-cell transplantations that myeloproliferative neoplasm (MPN) disease, manifesting either as erythrocytosis or thrombocytosis, can be initiated clonally from a single cell carrying JAK2-V617F. However, only a subset of mice reconstituted from single hematopoietic stem cells displayed MPN phenotype. [J Exp Med] Abstract Dynamic Shifts in Occupancy by TAL1 Are Guided by GATA Factors and Drive Large-Scale Reprogramming of Gene Expression during Hematopoiesis Scientists combined ChIP-seq and RNA-seq data in six mouse cell types representing a progression from multilineage precursors to differentiated erythroblasts and megakaryocytes. They found that sites of occupancy shift dramatically during commitment to the erythroid lineage, vary further during terminal maturation, and are strongly associated with changes in gene expression. [Genome Res] Abstract | Full Article Determining C-Myb Protein Levels Can Isolate Functional Hematopoietic Stem Cell Subtypes Scientists generated a novel c-myb allele in mice that allows direct observation of c-Myb protein levels in single cells. Using this reporter line they demonstrate that subtypes of hematopoietic stem cells can be isolated based upon their respective c-Myb protein expression levels. [Stem Cells] Abstract Medicarpin, a Legume Phytoalexin Sensitizes Myeloid Leukemia Cells to TRAIL-Induced Apoptosis through the Induction of DR5 and Activation of the ROS-JNK-CHOP Pathway Researchers report that medicarpin, a naturally occurring phytoalexin, sensitizes myeloid leukemia cells to tumor necrosis factor α-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. [Cell Death Dis] Full Article Small Molecule Inhibitor of Glycogen Synthase Kinase 3β 6-Bromoindirubin-3-Oxime Inhibits Hematopoietic Regeneration in Stem Cell Recipient Mice Scientists investigated the effect of glycogen synthase kinase 3β inhibitor 6-bromoindirubin-3-oxime previously shown to inhibit leukemia cell growth in vitro and animal models on hematopoietic regeneration in recipients of stem cell transplant. [Stem Cells Dev] Abstract Upregulation of CD11A on Hematopoietic Stem Cells Denotes the Loss of Long-Term Reconstitution Potential Researchers describe a marker, CD11A, which allows for the enhanced purification of mouse hematopoietic stem cells (HSCs). They show through in vivo transplantations that upregulation of CD11A on HSCs denotes the loss of their long-term reconstitution potential. [Stem Cells Rep] Full Article Chaetocin Antileukemia Activity against Chronic Myelogenous Leukemia Cells Is Potentiated by Bone Marrow Stromal Factors and Overcomes Innate Imatinib Resistance Scientists show that chaetocin suppressed viability and colony formation, and induced apoptosis of the murine hematopoietic cell line TonB210 with and without Bcr-Abl expression, and these effects were potentiated by bone marrow stromal cytokines and growth factors. [Oncogenesis] Full Article CLINICAL RESEARCH HLA-C Expression Levels Define Permissible Mismatches in Hematopoietic Cell Transplantation Researchers examined the role for HLA-C expression levels to identify permissible HLA-C mismatches. The median fluorescence intensity, a proxy of HLA-C expression, was assigned to each HLA-C allotype in 1975 patients and their HLA-C-mismatched unrelated transplant donors. [Blood] Abstract Elevated Fluoride Levels and Periostitis in Pediatric Hematopoietic Stem Cell Transplant Recipients Receiving Long-Term Voriconazole Scientists review fluoride levels, clinical, and laboratory data in five pediatric hematopoietic stem cell transplant recipients on long-term voriconazole therapy, all found to have elevated serum fluoride levels. [Pediatr Blood Cancer] Abstract |