The platelet glycoprotein IIb (αIIb; CD41) constitutes the alpha subunit of a highly expressed platelet surface integrin protein. We demonstrate that CD41 serves as the earliest marker of primitive erythroid progenitor cells in the embryonic day 7 (E7.0) yolk sac and high-level expression identifies essentially all E8.25 yolk sac definitive hematopoietic progenitors. Some definitive hematopoietic progenitor cells in the fetal liver and bone marrow also express CD41. Hematopoietic stem cell competitive repopulating ability is present in CD41 dim and CD41 lo/-cells isolated from bone marrow and fetal liver cells, however, activity is enriched in the CD41 lo/-cells. CD41 bright yolk sac definitive progenitor cells co-express CD61 and bind fibrinogen, demonstrating receptor function. Thus, CD41 expression marks the onset of primitive and definitive hematopoiesis in the murine embryo and persists as a marker of some stem and progenitor cell populations in the fetal liver and adult marrow, suggesting novel roles for this integrin.

The majority of B lymphocytes in the adult mouse are generated in the bone marrow from hematopoietic stem cells (HSCs) that first appear in the aorta-gonado-mesonephros region of the fetus on embryonic day (E) 10.5-11. Comparatively less is known about B-cell development during embryogenesis. For example, which specific embryonic tissues participate in B lymphopoiesis and whether hematopoietic differentiation is skewed toward specific B-cell subsets in the embryo are unanswered questions, because the systemic circulation is initiated early during embryogenesis, resulting in an admixture of cells potentially originating from multiple sites. We demonstrate, using Ncx1 −/− mice that lack systemic blood circulation, that the E9 yolk sac (YS) and the intra-embryonic para-aortic splanchnopleura (P-Sp) tissues independently give rise to AA4.1lo-neg B progenitor cells that preferentially differentiate into innate type B-1 and marginal zone (MZ) B cells but not into B-2 cells upon transplantation. We have further demonstrated that these B-1 progenitor cells arise directly from YS and P-Sp hemogenic endothelium. These results document the initial wave of innate B lymphopoietic progenitor cells available for seeding the fetal liver at E11. The results of these studies expand our knowledge of hemogenic endothelial sites specifying distinct B-1 and MZ cell fates apart from B-2 cells and independent of an HSC origin during development.B-1 cell | marginal zone B cell | OP9 stromal cells | hematopoiesis

Background Bronchopulmonary dysplasia and emphysema are life-threatening diseases resulting from impaired alveolar development or alveolar destruction. Both conditions lack effective therapies. Angiogenic growth factors promote alveolar growth and contribute to alveolar maintenance. Endothelial colony-forming cells (ECFCs) represent a subset of circulating and resident endothelial cells capable of self-renewal and de novo vessel formation. We hypothesized that resident ECFCs exist in the developing lung, that they are impaired during arrested alveolar growth in experimental bronchopulmonary dysplasia, and that exogenous ECFCs restore disrupted alveolar growth. Methods and Results Human fetal and neonatal rat lungs contain ECFCs with robust proliferative potential, secondary colony formation on replating, and de novo blood vessel formation in vivo when transplanted into immunodeficient mice. In contrast, human fetal lung ECFCs exposed to hyperoxia in vitro and neonatal rat ECFCs isolated from hyperoxic alveolar growth–arrested rat lungs mimicking bronchopulmonary dysplasia proliferated less, showed decreased clonogenic capacity, and formed fewer capillary-like networks. Intrajugular administration of human cord blood–derived ECFCs after established arrested alveolar growth restored lung function, alveolar and lung vascular growth, and attenuated pulmonary hypertension. Lung ECFC colony- and capillary-like network-forming capabilities were also restored. Low ECFC engraftment and the protective effect of cell-free ECFC-derived conditioned media suggest a paracrine effect. Long-term (10 months) assessment of ECFC therapy showed no adverse effects with persistent improvement in lung structure, exercise capacity, and pulmonary hypertension. Conclusions Impaired ECFC function may contribute to arrested alveolar growth. Cord blood–derived ECFC therapy may offer new therapeutic options for lung diseases characterized by alveolar damage.

Lysosomal acid lipase (LAL) is a key enzyme that

SIRT1 is a founding member of a sirtuin family of 7 proteins and histone deacetylases. It is involved in cellular resistance to stress, metabolism, differentiation, aging, and tumor suppression. SIRT1 ؊/؊ mice demonstrate embryonic and postnatal development defects. We examined hematopoietic and endothelial cell differentiation of SIRT1 ؊/؊ mouse embryonic stem cells (ESCs) in vitro, and hematopoietic progenitors in SIRT1 ؉/؉ , ؉/؊ , and ؊/؊ mice. SIRT1 ؊/؊ ESCs formed fewer mature blast cell colonies. Replated SIRT1 ؊/؊ blast colony-forming cells demonstrated defective hematopoietic potential. Endothelial cell production was unaltered, but there were defects in formation of a primitive vascular network from SIRT1 ؊/؊ -derived embryoid bodies. Development of primitive and definitive progenitors derived from SIRT1 ؊/؊ ESCs were also delayed and/or defective. Differentiation delay/defects were associated with delayed capacity to switch off Oct4, Nanog and Fgf5 expression, decreased ␤-H1 globin, ␤-major globin, and Scl gene expression, and reduced activation of Erk1/2. Ectopic expression of SIRT1 rescued SIRT1 ؊/؊ ESC differentiation deficiencies. SIRT1 ؊/؊ yolk sacs manifested fewer primitive erythroid precursors. SIRT1 ؊/؊ and SIRT1 ؉/؊ adult marrow had decreased numbers and cycling of hematopoietic progenitors, effects more apparent at 5%, than at 20%, oxygen tension, and these progenitors survived less well in vitro under conditions of delayed growth factor addition. This suggests a role for SIRT1 in ESC differentiation and mouse hematopoiesis. (Blood. 2011;117(2):440-450) IntroductionMouse embryonic stem cells (ESCs) are pluripotent with capacity for unlimited self-renewal or differentiation into endoderm, ectoderm, and mesoderm. Self-renewal behavior in vitro is sustained with leukemia inhibitory factor (LIF). 1 With removal of LIF and in the absence of feeder layer cells, ESCs grow into spheres termed embryoid bodies (EBs), which generate hematopoietic and endothelial progeny recapitulating development of those populations in the yolk sac. 2 Hemangioblasts generate blast colonies in vitro displaying hematopoietic and endothelial potential. 3 The ESC/EB system provides a powerful in vitro model to explore cellular and molecular events that specify lineage choice and hematopoietic commitment.Sirtuins, or Sir2 family proteins, are conserved from bacteria to humans. 4 Sir2 modulates longevity and aging in yeast, Caenorhabditis elegans, and Drosophila. 5 Mammalian homologs of Sir2 encompass a family of 7 proteins (SIRT1-SIRT7), among which SIRT1 is the closest human homolog of the yeast Sir2 protein. 4 SIRT1 deacetylates proteins, including p53 and FOXO transcription factors, and plays many key functions including energy metabolism, differentiation, aging, and tumor suppression. [6][7][8][9][10] SIRT1 is expressed at high levels in mouse embryos with the highest SIR2␣ mRNA expression is embryonic day (E) 4.5 embryos. Although expression is down-regulated during subsequent embryogenesis, high level expression rema...

Significance All lymphoid cells are considered to be products of hematopoietic stem cells (HSCs); however, it has been suggested, but not proven, that innate immune B-1 progenitor cells develop independently of HSCs in the fetal liver. B-1 cells, especially B-1a cells, are not replaced by adult bone marrow transplantation. Thus, it is critical to understand the origin and mechanisms required to sustain these cells in vivo because B-1 cells play important roles in the first line of defense against microbial infection and in preventing organ damage in autoimmune patients and infections in some patients after bone-marrow transplantation. We demonstrate that B-1 progenitor cells can develop independently of HSCs in the fetal liver and that their development relies critically on the expression of core-binding factor beta.

Zfp36l2 KO fetal liver hematopoietic stem cells were unable to adequately reconstitute the hematopoietic system of lethally irradiated recipients. These data establish Zfp36l2 as a critical modulator of definitive hematopoiesis and suggest a novel regulatory pathway involving control of mRNA stability in the life cycle of hematopoietic stem and progenitor cells.

Hematopoietic and endothelial cells may be derived from a common precursor cell (hemangioblast) during embryogenesis; however, some evidence suggests that hematopoietic cells may emerge from endothelial cells. The onset of definitive hematopoiesis at E8.25 in the murine embryo is marked by high-level CD41 expression. We questioned whether these hematopoietic cells were derived directly from mesoderm cells or emerged from endothelium. At 8.25 days post coitus (dpc), CD41 was coexpressed with CD31, CD34, and Flk1 in some intraluminal round cells that appeared to arise from flattened endothelial cells lining yolk sac capillary vessels. Cell-sorting studies revealed that all subpopulations of cells expressing CD41 possessed hematopoietic activity. Surprisingly, Tie2(+)Flk1(+) cells, a phenotype enriched in adult endothelial progenitors, also displayed some hematopoietic progenitor activity in vitro, but this activity was restricted to the CD41(+) fraction; only endothelial cells were derived from freshly isolated Tie2 (+)Flk1(bright) CD41() cells. Tie2(+)Flk1(dim)CD41() 8.25-dpc yolk sac cells devoid of hematopoietic progenitor activity gave rise to endothelial-like capillary networks in vitro and differentiated upon co-culture with OP9 stromal cells into definitive hematopoietic progenitors. These results demonstrate that CD41-expressing definitive hematopoietic cells appear to arise from endothelial cells lining nascent capillaries in vivo.