Role of PDGF-B/PDGFR: signalling in definitive haematopoiesis

The first haematopoietic stem cells (HSCs) are generated in the dorsal aorta (DA) of the midgestation mouse embryo. Signals from the microenvironment are required for HSC generation. However, the signals and identity of cells releasing them in vivo remain unknown. In the present work, we identified at least three populations of perivascular cells surrounding the DA based on the expression of the perivascular cell markers NG2, PDGFRβ and αSMA. NG2+ PDGFRβ+ αSMA+ pericytes/vascular smooth muscle cells (PCs/vSMCs) and NG2- PDGFRβ+ αSMA- sub-pericytes (Sub-PCs) were found to be enriched in HSC-supportive genes described in the adult bone marrow (BM). As both populations express PDGFRβ, which has recently been shown to mediate HSC specification in zebrafish, and PDGF-B/PDGFRβ signalling is also required for the recruitment of pericytes to the developing blood vessel wall, we hypothesised that PDGF-B/PDGFRβ signalling is required to generate the first HSCs in vivo. To answer this question, we used PDGFRβ knock-out (KO) and PDGF-Bret KO mice, both of which have a defective pericyte recruitment to blood vessels and defective or absent PDGF-B/PDGFRβ signalling. Results from our haematopoietic progenitor assays (CFU-Cs) and transplantations show that the germline deletion of PDGFRβ affects both haematopoietic progenitor numbers and HSC activity in the E11 AGM. HSPCs in other haematopoietic organs are not affected at this stage. PDGF-Bret KO mice showed no defects in midgestation HSPCs, but AGM HSCs failed to reconstitute secondary recipients. Together, these data suggest that PDGFB/PDGFRβ signalling is required for AGM haematopoiesis. We found that perivascular stromal cells surrounding the DA are not affected by these mutations, nor the integrity of the blood vessel, suggesting that PDGFB/PDGFRβ signalling is not required for PC/vSMCs recruitment to the DA. We therefore hypothesised that PDGF-B/PDGFRβ signalling is either required in the niche for HSC specification and/or generation, and/or that PDGFRβ+ cells are precursors of HSCs. Tracing experiments using PDGFRβ-Cre;TdTomato mice found that a subset of AGM HSPCs derive from PDGFRβ-Cre precursors and that both Tomato- and Tomato+ E14 foetal liver (FL) and BM cells reconstitute irradiated recipients. Together these data suggest that adult HSCs have distinct developmental origins, one of them deriving from PDGFRβ+ cells. In conclusion, our results define PDGFRβ signalling as a key component of the HSC generating niche in the mouse embryo, and that a subset of HSCs derive from PDGFRβ+ precursors

Palynotaxonomy of the genus Gladiopappus (Dicomeae, Asteraceae) with special emphasis on the exine ultrastructure and mesoapertures

The pollen morphology of Gladiopappus vernonioides was studied with transmission (TEM) and scanning (SEM) electron microscopy and with light microscopy (LM). An Anthemoid pattern of exine ultrastructure was found. The pollen morphology of Gladiopappus supports the inclusion of this genus in the tribe Dicomeae and subtribe Dicominae but not in the Mutisieae s.str. The apertural system of G. vernonioides includes a mesoaperture that intersects the foot layer and the upper layer of the endexine, a condition already pointed out for several tribes of Asteroideae (Helenieae, Gnaphaliinae, Heliantheae, Inuleae, Senecioneae) and Carduoideae (Cardueae, Dicomeae). It is suggested that the existence of an intermediate aperture could characterize the apertural system of the Asteraceae as a synapomorphyS

Runx1+ vascular smooth muscle cells are essential for hematopoietic stem and progenitor cell development in vivo

Hematopoietic stem cells (HSCs) produce all essential cellular components of the blood. Stromal cell lines supporting HSCs follow a vascular smooth muscle cell (vSMC) differentiation pathway, suggesting that some hematopoiesis-supporting cells originate from vSMC precursors. These pericyte-like precursors were recently identified in the aorta-gonad-mesonephros (AGM) region; however, their role in the hematopoietic development in vivo remains unknown. Here, we identify a subpopulation of NG2 +Runx1 + perivascular cells that display a sclerotome-derived vSMC transcriptomic profile. We show that deleting Runx1 in NG2 + cells impairs the hematopoietic development in vivo and causes transcriptional changes in pericytes/vSMCs, endothelial cells and hematopoietic cells in the murine AGM. Importantly, this deletion leads also to a significant reduction of HSC reconstitution potential in the bone marrow in vivo. This defect is developmental, as NG2 +Runx1 + cells were not detected in the adult bone marrow, demonstrating the existence of a specialised pericyte population in the HSC-generating niche, unique to the embryo. </p

Runx1+ vascular smooth muscle cells are essential for hematopoietic stem and progenitor cell development in vivo

Abstract Hematopoietic stem cells (HSCs) produce all essential cellular components of the blood. Stromal cell lines supporting HSCs follow a vascular smooth muscle cell (vSMC) differentiation pathway, suggesting that some hematopoiesis-supporting cells originate from vSMC precursors. These pericyte-like precursors were recently identified in the aorta-gonad-mesonephros (AGM) region; however, their role in the hematopoietic development in vivo remains unknown. Here, we identify a subpopulation of NG2+Runx1+ perivascular cells that display a sclerotome-derived vSMC transcriptomic profile. We show that deleting Runx1 in NG2+ cells impairs the hematopoietic development in vivo and causes transcriptional changes in pericytes/vSMCs, endothelial cells and hematopoietic cells in the murine AGM. Importantly, this deletion leads also to a significant reduction of HSC reconstitution potential in the bone marrow in vivo. This defect is developmental, as NG2+Runx1+ cells were not detected in the adult bone marrow, demonstrating the existence of a specialised pericyte population in the HSC-generating niche, unique to the embryo

PDGFRβ+ cells play a dual role as hematopoietic precursors and niche cells during mouse ontogeny

Hematopoietic stem cell (HSC) generation in the aorta-gonad-mesonephros region requires HSC specification signals from the surrounding microenvironment. In zebrafish, PDGF-B/PDGFR beta signaling controls hematopoietic stem/progenitor cell (HSPC) generation and is required in the HSC specification niche. Little is known about murine HSPC specification in vivo and whether PDGF-B/PDGFR beta is involved. Here, we show that PDGFR beta is expressed in distinct perivascular stromal cell layers surrounding the mid-gestation dorsal aorta, and its deletion impairs hematopoiesis. We demonstrate that PDGFR beta(+) cells play a dual role in murine hematopoiesis. They act in the aortic niche to support HSPCs, and in addition, PDGFR beta(+) embryonic precursors give rise to a subset of HSPCs that persist into adulthood. These findings provide crucial information for the controlled production of HSPCs in vitro

Percursos DE educação linguística: uma homenagem a Maria Helena Ançã

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Comparative pollen morphology of the Iberian species of Pulicaria (Asteraceae, Inuleae, Inulinae) and its taxonomic significance

To better understand the taxonomy of Pulicaria, the pollen wall architecture of the six Iberian species were investigated using light (LM) and scanning electron microscopy (SEM). The exine structure of Pulicaria odora was also investigated using transmission electron microscopy (TEM). Statistical analysis was performed to distinguish taxonomically significant morphometric information from all the measured parameters of pollen grains. It was found that the exine sculpture characters, with special importance paid to the spines, were the most useful of all characters to define Pulicaria pollen types and separate the species. Three pollen types distinguishable through the spines morphology and the inter-spinular sculpture are described: P. microcephala pollen type (incl. P. microcephala), P. vulgaris pollen type (incl. P. vulgaris), and P. dysenterica pollen type (incl. P. dysenterica, P. odora, P. paludosa and P. sicula). A dichotomous key to these Pulicaria pollen types is proposed. The distribution of P. dysenterica, P. odora, P. paludosa and P. sicula in more than one leaf node in the classification tree reveals that the pollen grains of these species are difficult to segregate. Therefore, the construction of a satisfactory dichotomous key to the P. dysenterica pollen type species is not feasible. Yet, the different spines apex morphology between P. microcephala and P. paludosa and the existence of significant differences in five of the eight studied quantitative pollen characters of these two taxa, supports the opinion that the Berlengas Islands endemic P. microcephala should be accepted as a separate species. In addition, the differences among the spines morphology of P. vulgaris, P. microcephala, and the other four Iberian (and European) species, strengthen the conclusion that the section Pulicaria is non-monophyletic

The surgical safety checklist and patient outcomes after surgery: a prospective observational cohort study, systematic review and meta-analysis

© 2017 British Journal of Anaesthesia Background: The surgical safety checklist is widely used to improve the quality of perioperative care. However, clinicians continue to debate the clinical effectiveness of this tool. Methods: Prospective analysis of data from the International Surgical Outcomes Study (ISOS), an international observational study of elective in-patient surgery, accompanied by a systematic review and meta-analysis of published literature. The exposure was surgical safety checklist use. The primary outcome was in-hospital mortality and the secondary outcome was postoperative complications. In the ISOS cohort, a multivariable multi-level generalized linear model was used to test associations. To further contextualise these findings, we included the results from the ISOS cohort in a meta-analysis. Results are reported as odds ratios (OR) with 95% confidence intervals. Results: We included 44 814 patients from 497 hospitals in 27 countries in the ISOS analysis. There were 40 245 (89.8%) patients exposed to the checklist, whilst 7508 (16.8%) sustained ≥1 postoperative complications and 207 (0.5%) died before hospital discharge. Checklist exposure was associated with reduced mortality [odds ratio (OR) 0.49 (0.32–0.77); P\u3c0.01], but no difference in complication rates [OR 1.02 (0.88–1.19); P=0.75]. In a systematic review, we screened 3732 records and identified 11 eligible studies of 453 292 patients including the ISOS cohort. Checklist exposure was associated with both reduced postoperative mortality [OR 0.75 (0.62–0.92); P\u3c0.01; I2=87%] and reduced complication rates [OR 0.73 (0.61–0.88); P\u3c0.01; I2=89%). Conclusions: Patients exposed to a surgical safety checklist experience better postoperative outcomes, but this could simply reflect wider quality of care in hospitals where checklist use is routine