Decreased PGC1β expression results in disrupted human erythroid differentiation, impaired hemoglobinization and cell cycle exit.

Production of red blood cells relies on proper mitochondrial function, both for their increased energy demands during differentiation and for proper heme and iron homeostasis. Mutations in genes regulating mitochondrial function have been reported in patients with anemia, yet their pathophysiological role often remains unclear. PGC1β is a critical coactivator of mitochondrial biogenesis, with increased expression during terminal erythroid differentiation.

Yippee like 4 (Ypel4) is essential for normal mouse red blood cell membrane integrity.

The YPEL family genes are highly conserved across a diverse range of eukaryotic organisms and thus potentially involved in essential cellular processes. Ypel4, one of five YPEL family gene orthologs in mouse and human, is highly and specifically expressed in late terminal erythroid differentiation (TED). In this study, we investigated the role of Ypel4 in murine erythropoiesis, providing for the first time an in-depth description of a Ypel4-null phenotype in vivo.

Prospective isolation of radiation induced erythroid stress progenitors reveals unique transcriptomic and epigenetic signatures enabling increased erythroid output.

Massive expansion of erythroid progenitor cells is essential for surviving anemic stress. Research towards understanding this critical process, referred to as stress-erythropoiesis, has been hampered due to lack of specific marker-combinations enabling analysis of the distinct stress-progenitor cells capable of providing radioprotection and enhanced red blood cell production. Here we present a method for precise identification and in vivo validation of progenitor cells contributing to both steady-state and stress-erythropoiesis, enabling for the first time in-depth molecular characterization of these cells.

Technical considerations for the use of CRISPR/Cas9 in hematology research.

The hematopoietic system is responsible for transporting oxygen and nutrients, fighting infections, and repairing tissue damage. Hematopoietic system dysfunction therefore causes a range of serious health consequences. Lifelong hematopoiesis is maintained by repopulating multipotent hematopoietic stem cells (HSCs) that replenish shorter-lived, mature blood cell types.

The evolving view of the hematopoietic stem cell niche.

Hematopoietic stem cells (HSCs) reside in specialized microenvironments known as niches. The niche is essential to support HSC function and to maintain a correct balance between self-renewal and differentiation. Recent advances in defining different mesenchymal and endothelial bone marrow cell populations, as well as hematopoietic stem and progenitor cells, greatly enhanced our understanding of these niches and of the molecular mechanisms by which they regulate HSC function.

Defining the Minimal Factors Required for Erythropoiesis through Direct Lineage Conversion.

Erythroid cell commitment and differentiation proceed through activation of a lineage-restricted transcriptional network orchestrated by a group of well characterized genes. However, the minimal set of factors necessary for instructing red blood cell (RBC) development remains undefined. We employed a screen for transcription factors allowing direct lineage reprograming from fibroblasts to induced erythroid progenitors/precursors (iEPs).

Gene expression profiling to define the cell intrinsic role of the SKI proto-oncogene in hematopoiesis and myeloid neoplasms.

The proto-oncogene SKI is highly expressed in human myeloid leukemia and also in murine hematopoietic stem cells. However, its operative relevance in these cells remains elusive. We have over-expressed SKI to define its intrinsic role in hematopoiesis and myeloid neoplasms, which resulted in a robust competitive advantage upon transplantation, a complete dominance of the stem and progenitor compartments, and a marked enhancement of myeloid differentiation at the expense of other lineages.

Two new routes to make blood: Hematopoietic specification from pluripotent cell lines versus reprogramming of somatic cells.

Transplantation of hematopoietic stem cells (HSCs) to treat hematologic disorders is routinely used in the clinic. However, HSC therapy is hindered by the requirements of finding human leukocyte antigen (HLA)-matched donors and attaining sufficient numbers of long-term HSCs in the graft. Therefore, ex vivo expansion of transplantable HSCs remains one of the "holy grails" of hematology.

Oncostatin M acting via OSMR, augments the actions of IL-1 and TNF in synovial fibroblasts.

Objective: To identify how the gp130-signaling cytokine oncostatin M (OSM), acting alone or in concert with IL-1β or TNFα, affects synovial fibroblast expression of genes relevant to inflammation and bone erosion in inflammatory arthritis.

Methods: Synovial fibroblasts (SFs) were isolated from non-arthritic wild type (WT) or OSM receptor deficient (OSMR(-/-)) mice and stimulated with OSM, IL-1β or TNFα and their combinations. Cytokine gene expression was assessed by quantitative RT-PCR.

Defining the hematopoietic stem cell niche: the chicken and the egg conundrum.

Understanding the in vivo regulation of hematopoietic stem cells (HSCs) will be critical to identifying key factors involved in the regulation of HSC self-renewal and differentiation. The niche (microenvironment) in which HSCs reside has recently regained attention accompanied by a dramatic increase in the understanding of the cellular constituents of the bone marrow HSC niche. The use of sophisticated genetic models allowing modulation of specific lineages has demonstrated roles for mesenchymal-derived elements such as osteoblasts and adipocytes, vasculature, nerves, and a range of hematopoietic progeny of the HSC as being participants in the regulation of the bone marrow microenvironment.

Erythropoietin couples erythropoiesis, B-lymphopoiesis, and bone homeostasis within the bone marrow microenvironment.

Erythropoietin (Epo) has been used in the treatment of anemia resulting from numerous etiologies, including renal disease and cancer. However, its effects are controversial and the expression pattern of the Epo receptor (Epo-R) is debated. Using in vivo lineage tracing, we document that within the hematopoietic and mesenchymal lineage, expression of Epo-R is essentially restricted to erythroid lineage cells.

Canonical BMP signaling is dispensable for hematopoietic stem cell function in both adult and fetal liver hematopoiesis, but essential to preserve colon architecture.

Numerous publications have described the importance of bone morphogenetic protein (BMP) signaling in the specification of hematopoietic tissue in developing embryos. Here we investigate the full role of canonical BMP signaling in both adult and fetal liver hematopoiesis using conditional knockout strategies because conventional disruption of components of the BMP signaling pathway result in early death of the embryo. By targeting both Smad1 and Smad5, we have generated a double-knockout mouse with complete disruption of canonical BMP signaling.

Endoglin is not critical for hematopoietic stem cell engraftment and reconstitution but regulates adult erythroid development.

Endoglin is a transforming growth factor-beta (TGF-beta) accessory receptor recently identified as being highly expressed on long-term repopulating hematopoietic stem cells (HSC). However, little is known regarding its function in these cells. We have used two complementary approaches toward understanding endoglin's role in HSC biology: one that efficiently knocks down expression via lentiviral-driven short hairpin RNA and another that uses retroviral-mediated overexpression.

Smad4 is critical for self-renewal of hematopoietic stem cells.

Members of the transforming growth factor beta (TGF-beta) superfamily of growth factors have been shown to regulate the in vitro proliferation and maintenance of hematopoietic stem cells (HSCs). Working at a common level of convergence for all TGF-beta superfamily signals, Smad4 is key in orchestrating these effects. The role of Smad4 in HSC function has remained elusive because of the early embryonic lethality of the conventional knockout.

Smad7 promotes self-renewal of hematopoietic stem cells.

The Smad-signaling pathway downstream of the transforming growth factor-beta superfamily of ligands is an evolutionarily conserved signaling circuitry with critical functions in a wide variety of biologic processes. To investigate the role of this pathway in the regulation of hematopoietic stem cells (HSCs), we have blocked Smad signaling by retroviral gene transfer of the inhibitory Smad7 to murine HSCs. We report here that the self-renewal capacity of HSCs is promoted in vivo upon blocking of the entire Smad pathway, as shown by both primary and secondary bone marrow (BM) transplantations.

Smad5 is dispensable for adult murine hematopoiesis.

Smad5 is known to transduce intracellular signals from bone morphogenetic proteins (BMPs), which belong to the transforming growth factor-beta (TGF-beta) superfamily and are involved in the regulation of hematopoiesis. Recent findings suggest that BMP4 stimulates proliferation of human primitive hematopoietic progenitors in vitro, while early progenitors from mice deficient in Smad5 display increased self-renewal capacity in murine embryonic hematopoiesis. Here, we evaluate the role of Smad5 in the regulation of hematopoietic stem cell (HSC) fate decisions in adult mice by using an inducible MxCre-mediated conditional knockout model.