SummaryHematopoiesis is a multistage process involving the differentiation of stem and progenitor cells into distinct mature cell lineages. Here we present Haemopedia, an atlas of murine gene-expression data containing 54 hematopoietic cell types, covering all the mature lineages in hematopoiesis. We include rare cell populations such as eosinophils, mast cells, basophils, and megakaryocytes, and a broad collection of progenitor and stem cells. We show that lineage branching and maturation during hematopoiesis can be reconstructed using the expression patterns of small sets of genes. We also have identified genes with enriched expression in each of the mature blood cell lineages, many of which show conserved lineage-enriched expression in human hematopoiesis. We have created an online web portal called Haemosphere to make analyses of Haemopedia and other blood cell transcriptional datasets easier. This resource provides simple tools to interrogate gene-expression-based relationships between hematopoietic cell types and genes of interest.

Down syndrome is characterized by multiple phenotypic manifestations associated with trisomy of chromosome 21. The transient myeloproliferative disorder and acute megakaryocytic leukemia associated with Down syndrome are uniquely associated with mutations in the transcription factor GATA1; however, the identity of trisomic genes on chromosome 21 that predispose to these hematologic disorders remains unknown. IntroductionDown syndrome (DS) is uniquely associated with a transient myeloproliferative disorder (DS-TMD) and acute megakaryocytic leukemia (DS-AMKL). 1 Increased dosage of genes within chromosome 21 (Hsa21), including AML1/RUNX1, ETS2, and ERG, has been postulated to cooperate with an acquired GATA1 mutation to generate DS-TMD and DS-AMKL, 2 although direct evidence identifying critical genes is lacking.A member of the ETS family of transcription factors, 3 ERG is necessary for normal platelet development and stem cell function 4 and has been implicated in the pathogenesis of human leukemia. [5][6][7] Located on the long arm of Hsa21, 8 evidence for a role of ERG in the development of human DS-TMD and DS-AMKL arose from detection of ERG expression in human acute megakaryoblastic leukemia cell lines and primary human samples of DS-AMKL and DS-TMD. 2 In vitro, overexpression of ERG can induce megakaryocytic differentiation of human cell lines and murine fetal liver progenitors, 4,9,10 and can interact with GATA1 mutations to immortalize fetal liver progenitors. 9,10 The Ts(17 16 )65Dn mouse is a well-characterized model of DS containing a trisomic chromosomal Down syndrome critical region (DSCR) syntenic to Hsa21, including 94 orthologs of the 170 genes within Hsa21. 11 Ts(17 16 )65Dn mice develop a highly penetrant myeloproliferative disorder (MPD), 12 supporting the contention that trisomy of critical gene(s) within Hsa21 can lead to hyperproliferation and megakaryocytic differentiation, and may therefore predispose to the development and phenotype of the megakaryoblasts observed with human DS-TMD and DS-AMKL.To determine whether trisomy of functional Erg drives the development of the myeloproliferative phenotype observed in Ts(17 16 )65Dn mice, trisomic Ts(17 16 )65Dn mice were crossed to mice carrying the loss-of-function Erg mld2 mutation that contains a S329P nontransactivating missense mutation in the DNA-binding region of Erg, 4 to generate mice disomic for functional Erg but trisomic for all other genes within the DSCR of Ts(17 16 )65Dn. Methods MiceDerivation and genotyping of the Erg mld2 mutant allele has been described. 4 Ts(17 16 )65Dn mice (The Jackson Laboratory) were maintained on an F1 background of C57BL/6JEiJ and C3HHeSnJ. All mice were derived from the first-generation progeny of matings between Erg ϩ/mld2 and Ts (17 16 ) Hematology and histologyBlood was collected into tubes containing ethylenediaminetetraacetic acid (Becton Dickinson) and analyzed with an Advia 120 analyzer (Bayer). Singlecell suspensions from 1 femur and spleen were collected in balanced salts solution (0.15M NaC...

Navitoclax (ABT-263), an inhibitor of the pro-survival BCL-2 family proteins BCL-2, BCL-XL and BCL-W, has shown clinical efficacy in certain BCL-2-dependent haematological cancers, but causes dose-limiting thrombocytopaenia. The latter effect is caused by Navitoclax directly inducing the apoptotic death of platelets, which are dependent on BCL-XL for survival. Recently, ABT-199, a selective BCL-2 antagonist, was developed. It has shown promising anti-leukaemia activity in patients whilst sparing platelets, suggesting that the megakaryocyte lineage does not require BCL-2. In order to elucidate the role of BCL-2 in megakaryocyte and platelet survival, we generated mice with a lineage-specific deletion of Bcl2, alone or in combination with loss of Mcl1 or Bclx. Platelet production and platelet survival were analysed. Additionally, we made use of BH3 mimetics that selectively inhibit BCL-2 or BCL-XL. We show that the deletion of BCL-2, on its own or in concert with MCL-1, does not affect platelet production or platelet lifespan. Thrombocytopaenia in Bclx-deficient mice was not affected by additional genetic loss or pharmacological inhibition of BCL-2. Thus, BCL-2 is dispensable for thrombopoiesis and platelet survival in mice.