Search

Epigenetic mechanisms regulate the multilineage differentiation capacity of hematopoietic stem cells (HSCs) into a variety of blood and immune cells. Mapping the chromatin dynamics of functionally defined cell populations will shed mechanistic insight into 2 major, unanswered questions in stem cell biology: how does epigenetic identity contribute to a cell type’s lineage potential, and how do cascades of chromatin remodeling dictate ensuing fate decisions? Our recent work revealed evidence of multilineage gene priming in HSCs, where open cis-regulatory elements (CREs) exclusively shared between HSCs and unipotent lineage cells were enriched for DNA binding motifs of known lineage-specific transcription factors. Oligopotent progenitor populations operating between the HSCs and unipotent cells play essential roles in effecting hematopoietic homeostasis. To test the hypothesis that selective HSC-primed lineage-specific CREs remain accessible throughout differentiation, we used ATAC-seq to map the temporal dynamics of chromatin remodeling during progenitor differentiation. We observed epigenetic-driven clustering of oligopotent and unipotent progenitors into distinct erythromyeloid and lymphoid branches, with multipotent HSCs and MPPs associating with the erythromyeloid lineage. We mapped the dynamics of lineage-primed CREs throughout hematopoiesis and identified both unique and shared CREs as potential lineage reinforcement mechanisms at fate branch points. Additionally, quantification of genome-wide peak count and size revealed overall greater chromatin accessibility in HSCs, allowing us to identify HSC-unique peaks as putative regulators of self-renewal and multilineage potential. Finally, CRISPRi-mediated targeting of ATACseq-identified putative CREs in HSCs allowed us to demonstrate the functional role of selective CREs in lineage-specific gene expression. These findings provide insight into the regulation of stem cell multipotency and lineage commitment throughout hematopoiesis and serve as a resource to test functional drivers of hematopoietic lineage fate.

We investigate the importance of spatial, material, and organisational factors to gendered peer relations on the school football pitch. The study is part of an ethnographic research project exploring the relations between school bullying and the institutional context of schooling, focusing on the perspectives of teachers and pupils from preschool class up to grade eight (approximately ages 5-13). The findings in this study are based on participant observations and semi-structured interviews with pupils at three schools in Sweden. Our findings illustrate how social-ecological elements of spatial, material, and organisational factors such as school design, the material construction of the pitches, and the temporal organisation of the space through scheduling promote gendered positioning and fevered interactions which influence peer relations and sometimes contribute to degrading treatment, harassment and bullying. Our study demonstrates how these processes need to be understood as complexly related to social-ecological factors beyond the football pitch setting.

School climate is crucial for understanding everyday school life. For pupils, breaktime seems to be associated with how they feel about their school climate. To better understand school climate and what social processes pupils address, this study explores pupils perspectives on school climate with attention on how they perceive their breaktimes. The study was based on 29 focus group interviews (n = 164) with pupils from two public schools in grades 1-9 (i.e. 7-15 years old). Constructivist grounded theory guided data gathering and analysis. Findings revealed how breaktime was an indicator of how pupils perceived their school climate, but their perceptions were dynamic. We conceptualised breaktime as a social process influenced by three main categories: peer climate, levels of unsafe incidents, and availability of activities. We adopted a social-ecological perspective to conceptualise how pupils perceptions of breaktimes varied due to how breaktimes were nested within different social-ecological systems. Funding: Swedish Institute for Educational Research [2017-00038]

Constructivist grounded theory has earned a place in research worldwide and been applied in diverse fields. However, in educational research of teachers’ work in the classroom from the perspective of the teacher, it has had a lesser impact on research methodology. We argue for the benefits to educational research when using a constructivist grounded theory methodology. Our arguments focus on three concrete benefits: (1) Constructivist grounded theory focuses on participants’ perspectives, or main concerns, (2) by using an open, exploratory approach, and, (3) could involve investigating the relationships between the focused codes, preferably by using theoretical coding. We argue that constructivist grounded theory adds an analytical edge to work in classrooms, when skilfully deployed. These benefits with constructivist grounded theory differentiate the approach against other qualitative methods. Another important feature is focusing on the actions, and social processes, and thus making use of several theoretical codes. As we will outline in this paper, these features of constructivist grounded theory could help produce theoretical insights that could be valuable additions to educational research and educational practices

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas genome engineering has emerged as a powerful tool to modify precise genomic sequences with unparalleled accuracy and efficiency. Major advances in CRISPR technologies over the last 5 years have fueled the development of novel techniques in hematopoiesis research to interrogate the complexities of hematopoietic stem cell (HSC) biology. In particular, high throughput CRISPR based screens using various "flavors" of Cas coupled with sequencing and/or functional outputs are becoming increasingly efficient and accessible. In this review, we discuss recent achievements in CRISPR-mediated genomic engineering and how these new tools have advanced the understanding of HSC heterogeneity and function throughout life. Additionally, we highlight how these techniques can be used to answer previously inaccessible questions and the challenges to implement them. Finally, we focus on their translational potential to both model and treat hematological diseases in the clinic.

Hematopoietic stem cells (HSCs) have been studied extensively since their initial functional description in 1961 when Dr. James Till and Dr. Ernest McCulloch developed the first in vivo clonal strategy, termed the "spleen colony-forming unit" (CFU-S) assay, to assess the functional capacity of bone marrow–derived hematopoietic progenitors at the single-cell level. Through transplantation of bone marrow cells and analysis of the resulting cellular nodules in the spleen, the CFU-S assay revealed both the self-renewal and clonal differentiation capacity of hematopoietic progenitors. Further development and use of this assay have identified highly proliferative, self-renewing, and differentiating HSCs that possess clonal, multilineage differentiation. The CFU-S strategy has also been adapted to interrogating single purified hematopoietic stem and progenitor cell populations, advancing our knowledge of the hematopoietic hierarchy. In this review, we explore the major discoveries made with the CFU-S assay, consider its modern use and recent improvements, and compare it with commonly used long-term transplantation assays to determine the continued value of the CFU-S assay for understanding HSC biology and hematopoiesis.

Simple Summary E-cigarettes have gained popularity as alternatives to traditional tobacco products over the past several decades. Despite being marketed as safer, they still contain several highly toxic compounds, which pose as dangers to human health. Nicotine is one of those toxic compounds and is known to have many deleterious effects on human health and disease susceptibility. Hematopoietic stem cells (HSCs) are the stem cells that give rise to the entire immune system and therefore serve as a compelling point of interrogation for the source of altered health and disease susceptibility in exposed individuals. Here we discuss how nicotine influences HSCs and the immune cells they make, as well as highlight potential mechanisms of altered immunity for life. Abstract Hematopoiesis is a tightly regulated process orchestrated by cell-intrinsic and cell-extrinsic cues. Over the past several decades, much effort has been focused on understanding how these cues regulate hematopoietic stem cell (HSC) function. Many endogenous key regulators of hematopoiesis have been identified and extensively characterized. Less is known about the mechanisms of long-term effects of environmental toxic compounds on hematopoietic stem and progenitor cells (HSPCs) and their mature immune cell progeny. Research over the past several decades has demonstrated that tobacco products are extremely toxic and pose huge risks to human health by causing diseases like cancer, respiratory illnesses, strokes, and more. Recently, electronic cigarettes have been promoted as a safer alternative to traditional tobacco products and have become increasingly popular among younger generations. Nicotine, the highly toxic compound found in many traditional tobacco products, is also found in most electronic cigarettes, calling into question their purported “safety”. Although it is known that nicotine is toxic, the pathophysiology of disease in exposed people remains under investigation. One plausible contributor to altered disease susceptibility is altered hematopoiesis and associated immune dysfunction. In this review, we focus on research that has addressed how HSCs and mature blood cells respond to nicotine, as well as identify remaining questions.

Background: School climate is crucial: its character can affect pupils academic achievement, teachers working conditions and the wellbeing of everyone at school. A major concern for teachers is how to prevent and manage disruptive behaviours. Against this backdrop, there is a need for thorough investigation of pupils perspectives to better understand their perceptions of the climate at their schools and their views about why disruptive behaviours occur. Purpose: In this small-scale, qualitative study, we aimed to contribute to the body of school climate research by exploring pupils perspectives on school climate, teachers and relationships at school. Method: We conducted an in-depth qualitative analysis, exploring pupils perspectives on these issues through focus group interviews. Eighteen semi-structured interviews were conducted (n = 104) with grade 1-9 (7- to 15-year-old) pupils from a school in Sweden. The interview guide included questions about sense of safety, relationships at school and in classrooms, and pupils views of teachers. Constructivist grounded theory was used as the analytical framework. Findings: A recurrent pattern identified in the data was the focus on disruptive behaviours and how these were connected to the pupils learning environment, sense of safety and teachers. Three core categories were conceptualised from the pupils perspectives: (a) within-pupil explanations, (b) teaching style explanations and (c) peer group process explanations. We adopted a social-ecological approach to conceptualise the complexities and interplay of factors addressed by the pupils in their perspectives on disruptive behaviours. Conclusions: Our findings provide insight into the way that different factors interplay in the emergence of disruptive behaviours in the classroom, nested within both contextual and structural aspects. This analysis of pupil perspectives also points to the importance of a whole-school approach in which teachers establish a warm, responsive and confident teaching style in the classroom and in the playground to influence the social dynamics.

Summary Age-related morbidity is associated with a decline in hematopoietic stem cell (HSC) function, but the mechanisms of HSC aging remain unclear. We performed heterochronic HSC transplants followed by quantitative analysis of cell reconstitution. Although young HSCs outperformed old HSCs in young recipients, young HSCs unexpectedly failed to outcompete the old HSCs of aged recipients. Interestingly, despite substantial enrichment of megakaryocyte progenitors (MkPs) in old mice in situ and reported platelet (Plt) priming with age, transplanted old HSCs were deficient in reconstitution of all lineages, including MkPs and Plts. We therefore performed functional analysis of young and old MkPs. Surprisingly, old MkPs displayed unmistakably greater regenerative capacity compared with young MkPs. Transcriptome analysis revealed putative molecular regulators of old MkP expansion. Collectively, these data demonstrated that aging affects HSCs and megakaryopoiesis in fundamentally different ways: whereas old HSCs functionally decline, MkPs gain expansion capacity upon aging., Graphical abstract, Highlights • Reconstitution deficit by old HSCs was observed by chimerism and absolute cell numbers • Young HSCs did not outcompete resident HSCs in aged recipient mice • Old MkPs display remarkable capacity to engraft, expand, and reconstitute platelets • Aging is associated with changes in MkP genome-wide expression signatures, Poscablo et al. explored age-related changes to hematopoietic stem cell and megakaryocyte progenitor (MkP) function. They found an unexpected gain of in vitro expansion and in vivo reconstitution potential of MkPs upon aging. These functional changes were accompanied by differences in transcriptome profiles between young and old MkPs, suggesting progenitor cell mechanisms contributing to hematopoietic aging.

The overall objective of this study was to examine the links between teacher–student relationship quality and student engagement, delimited to affective and behavioural engagement. We used a sequen...

Adult hematopoietic stem and progenitor cells (HSPCs) respond directly to inflammation and infection, resulting in both acute and persistent changes to quiescence, mobilization, and differentiation. Here we show that fetal HSPCs respond to prenatal inflammation in utero, and that the fetal response shapes postnatal hematopoiesis and immunity. Heterogenous fetal HSPCs showed divergent responses to maternal immune activation (MIA), including changes in quiescence, expansion, and lineage-biased output. Single cell transcriptomic analysis of fetal HSPCs in response to MIA revealed specific upregulation of inflammatory gene profiles in discrete, transient HSC populations, that propagated expansion of lymphoid-biased progenitors. Beyond fetal development, MIA caused the inappropriate expansion and persistence of fetal lymphoid-biased progenitors postnatally, concomitant with increased cellularity and hyperresponsiveness of fetal-derived innate-like lymphocytes. Our investigation demonstrates how inflammation in utero can direct the trajectory of output and function of fetal-derived immune cells by reshaping fetal HSC establishment.

Our respiratory system is vital to protect us from the surrounding nonsterile environment; therefore, it is critical for a state of homeostasis to be maintained through a balance of inflammatory cues. Recent studies have shown that actively transcribed noncoding regions of the genome are emerging as key regulators of biological processes, including inflammation. lincRNA-Cox2 is one such example of an inflammatory inducible long intergenic noncoding RNA functioning to fine-tune immune gene expression. Using bulk and single-cell RNA sequencing, in addition to FACS, we find that lincRNA-Cox2 is most highly expressed in the lung and is most upregulated after LPS-induced lung injury (acute lung injury [ALI]) within alveolar macrophages, where it functions to regulate inflammation. We previously reported that lincRNA-Cox2 functions to regulate its neighboring protein Ptgs2 in cis, and in this study, we use genetic mouse models to confirm its role in regulating gene expression more broadly in trans during ALI. Il6, Ccl3, and Ccl5 are dysregulated in the lincRNA-Cox2–deficient mice and can be rescued to wild type levels by crossing the deficient mice with our newly generated lincRNA-Cox2 transgenic mice, confirming that this gene functions in trans. Many genes are specifically regulated by lincRNA-Cox2 within alveolar macrophages originating from the bone marrow because the phenotype can be reversed by transplantation of wild type bone marrow into the lincRNA-Cox2–deficient mice. In conclusion, we show that lincRNA-Cox2 is a trans-acting long noncoding RNA that functions to regulate immune responses and maintain homeostasis within the lung at baseline and on LPS-induced ALI.

Adult hematopoietic stem and progenitor cells (HSPCs) respond directly to inflammation and infection, causing both acute and persistent changes to quiescence, mobilization, and differentiation. Here we show that murine fetal HSPCs respond to prenatal inflammation in utero and that the fetal response shapes postnatal hematopoiesis and immune cell function. Heterogeneous fetal HSPCs show divergent responses to maternal immune activation (MIA), including changes in quiescence, expansion, and lineage-biased output. Single-cell transcriptomic analysis of fetal HSPCs in response to MIA reveals specific upregulation of inflammatory gene profiles in discrete, transient hematopoietic stem cell (HSC) populations that propagate expansion of lymphoid-biased progenitors. Beyond fetal development, MIA causes the inappropriate expansion and persistence of fetal lymphoid-biased progenitors postnatally, concomitant with increased cellularity and hyperresponsiveness of fetal-derived innate-like lymphocytes. Our investigation demonstrates how inflammation in utero can direct the output and function of fetal-derived immune cells by reshaping fetal HSC establishment.

Recovery from pneumococcal pneumonia remodels the pool of alveolar macrophages so that they exhibit new surface marker profiles, transcriptomes, metabolomes, and responses to infection. Mechanisms mediating alveolar macrophage phenotypes after pneumococcal pneumonia have not been delineated. IFN-γ and its receptor on alveolar macrophages were essential for certain, but not all, aspects of the remodeled alveolar macrophage phenotype. IFN-γ was produced by CD4+ T cells plus other cells, and CD4+ cell depletion did not prevent alveolar macrophage remodeling. In mice infected or recovering from pneumococcus, monocytes were recruited to the lungs, and the monocyte-derived macrophages developed characteristics of alveolar macrophages. CCR2 mediated the early monocyte recruitment but was not essential to the development of the remodeled alveolar macrophage phenotype. Lineage tracing demonstrated that recovery from pneumococcal pneumonias converted the pool of alveolar macrophages from being primarily of embryonic origin to being primarily of adult hematopoietic stem cell origin. Alveolar macrophages of either origin demonstrated similar remodeled phenotypes, suggesting that ontogeny did not dictate phenotype. Our data reveal that the remodeled alveolar macrophage phenotype in lungs recovered from pneumococcal pneumonia results from a combination of new recruitment plus training of both the original cells and the new recruits.

C-X-C motif chemokine ligand 12 (CXCL12; aka SDF1α) is a major regulator of a number of cellular systems, including hematopoiesis, where it influences hematopoietic cell trafficking, proliferation, and survival during homeostasis and upon stress and disease. A variety of constitutive, temporal, ubiquitous, and cell-specific loss-of-function models have documented the functional consequences on hematopoiesis upon deletion of Cxcl12. Here, in contrast to loss-of-function experiments, we implemented a gain-of-function approach by generating a doxycycline-inducible transgenic mouse model that enables spatial and temporal overexpression of Cxcl12. We demonstrated that ubiquitous CXCL12 overexpression led to an increase in multipotent progenitors in the bone marrow and spleen. The CXCL12+ mice displayed reduced reconstitution potential as either donors or recipients in transplantation experiments. Additionally, we discovered that Cxcl12 overexpression improved hematopoietic stem and progenitor cell mobilization into the blood, and conferred radioprotection by promoting quiescence. Thus, this new CXCL12+ mouse model provided new insights into major facets of hematopoiesis and serves as a versatile resource for studying CXCL12 function in a variety of contexts.

Background Research suggests that negative peer interactions that compromise student safety and wellbeing often occur in spaces at school that are not easily visible, not adequately monitored, overcrowded and/or relatively unstructured. In a large online survey conducted in Swedish schools by the anti-bullying organisation, Friends, a small proportion of students indicated that they felt unsafe in the school canteen and responded to a question about why they felt unsafe there. As the canteen is often reported to be a space where negative peer interactions, such as harassment, bullying and other forms of school violence, occur, but little is known about why negative peer interactions occur there, we were particularly interested in exploring why some students perceived their school canteen to be an unsafe space. Purpose Taking a social-ecological perspective, our aim was to investigate why students reported feeling unsafe in the environment of the school canteen. Method In order to investigate this question, we analysed 1,547 responses from students in Swedish schools in grades 3-6 (ages 9-12). The responses were from the anti-bullying organisation Friends online questionnaires from 2011 to 2016. In the responses, students who indicated that they felt unsafe in the school canteen explained why they felt this way. Data were analysed qualitatively, using a six-step thematic approach. Findings The analysis identified four key themes: Space constraints, Time restrictions, The risk of social blunders and The negative actions of others. We discuss the findings in terms of the macrosystem, exosystem, mesosystem and microsystem. Conclusions In matters of student safety and wellbeing, we argue that it is not only important to consider the social context, but also how that context is interconnected with environmental and structural elements.

Hematopoietic stem cell (HSC) multipotency and self-renewal are typically defined through serial transplantation experiments. Host conditioning is necessary for robust HSC engraftment, likely by reducing immune-mediated rejection and by clearing limited HSC niche space. Because irradiation of the recipient mouse is non-specific and broadly damaging, there is a need to develop alternative models to study HSC performance at steady-state and in the absence of radiation-induced stress. We have generated and characterized two new mouse models where either all hematopoietic cells or only HSCs can be specifically induced to die in vivo or in vitro. Hematopoietic-specific Vav1-mediated expression of a loxP-flanked diphtheria-toxin receptor (DTR) renders all hematopoietic cells sensitive to diphtheria toxin (DT) in “Vav-DTR” mice. Crossing these mice to Flk2-Cre mice results in “HSC-DTR” mice which exhibit HSC-selective DT sensitivity. We demonstrate robust, rapid, and highly selective cell ablation in these models. These new mouse models provide a platform to test whether HSCs are required for long-term hematopoiesis in vivo, for understanding the mechanisms regulating HSC engraftment, and interrogating in vivo hematopoietic differentiation pathways and mechanisms regulating hematopoietic homeostasis.

While the efforts of teachers are crucial for preventing and stopping degrading treatment, harassment, and bullying in schools, research has found that teachers’ understandings of such terms may vary significantly. In this qualitative study, we take a social-ecological perspective to investigate Swedish schoolteachers’ understandings of the terms degrading treatment, harassment, and bullying. The study is based on ethnographic research, which included participant observations and interviews conducted at three schools. The findings demonstrate not only the ways in which teachers blurred the conceptual boundaries between degrading treatment, harassment, and bullying, but also how such blurring was influenced by factors within the microsystem, mesosystem, exosystem, macrosystem, and chronosystem, and how the juridification of degrading treatment and harassment encouraged teachers to construct hierarchies of what they perceived to be more or less serious incidents. Funding: Vetenskapsradet [2017-03604] Bullying arenas: A social-ecological investigation of school bullying

Tissue-resident lymphoid cells (TLCs) span the spectrum of innate-to-adaptive immune function. Unlike traditional, circulating lymphocytes that are continuously generated from hematopoietic stem cells (HSCs), many TLCs are of fetal origin and poorly generated from adult HSCs. Here, we sought to further understand murine TLC development and the roles of Flk2 and IL7Rα, two cytokine receptors with known function in traditional lymphopoiesis. Using Flk2- and Il7r-Cre lineage tracing, we found that peritoneal B1a cells, splenic marginal zone B (MZB) cells, lung ILC2s and regulatory T cells (Tregs) were highly labeled. Despite high labeling, loss of Flk2 minimally affected the generation of these cells. In contrast, loss of IL7Rα, or combined deletion of Flk2 and IL7Rα, dramatically reduced the number of B1a cells, MZBs, ILC2s and Tregs, both in situ and upon transplantation, indicating an intrinsic and essential role for IL7Rα. Surprisingly, reciprocal transplants of wild-type HSCs showed that an IL7Rα−/− environment selectively impaired reconstitution of TLCs when compared with TLC numbers in situ. Taken together, our data defined Flk2- and IL7Rα-positive TLC differentiation paths, and revealed functional roles of Flk2 and IL7Rα in TLC establishment.

Summary Hematopoietic stem cell (HSC) transplantation is a curative treatment for a variety of blood and immune disorders. Currently available methods to obtain donor HSCs are suboptimal, and the limited supply of donor HSCs hampers the success and availability of HSC transplantation therapies. We recently showed that manipulation of vascular integrity can be employed to induce HSC mobilization from the bone marrow to the blood stream, facilitating non-invasive collection of HSCs. Here, we tested whether FDA-approved vasodilators are capable of mobilizing HSCs. We found that a rapid, 2-h regimen of a single oral dose of Viagra (sildenafil citrate) combined with a single injection of the CXCR4 antagonist AMD3100 leads to efficient HSC mobilization at levels rivaling the standard-of-care 5-day regimen of granulocyte-colony stimulating factor (G-CSF/Filgrastim/Neupogen). Our findings solidify vascular integrity as an essential regulator of HSC trafficking and provide an attractive, single-day regimen for HSC mobilization using already FDA-approved drugs., Graphical Abstract, Highlights • Viagra enhances AMD3100-mediated HSC mobilization • Extremely rapid and efficient HSC mobilization with two FDA-approved drugs • Vascular integrity regulates HSC trafficking, In this article, Forsberg and colleagues demonstrate that Viagra, a widely used vasodilator, enhances Plerixafor-mediated hematopoietic stem cell (HSC) mobilization from the bone marrow to the blood stream. These findings solidify vascular integrity as an essential regulator of HSC trafficking and provide an attractive, single-day regimen for HSC mobilization using already FDA-approved drugs.

Summary Hematopoiesis is arguably one of the best understood stem cell systems; however, significant challenges remain to reach a consensus understanding of the lineage potential, heterogeneity, and relationships of hematopoietic stem and progenitor cell populations. To gain new insights, we performed quantitative analyses of mature cell production from hematopoietic stem cells (HSCs) and multiple hematopoietic progenitor populations. Assessment of the absolute numbers of mature cell types produced by each progenitor cell revealed a striking erythroid dominance of all myeloid-competent progenitors assessed, accompanied by strong platelet reconstitution. All populations with myeloid potential also produced robust numbers of red blood cells and platelets in vivo. Clonal analysis by single-cell transplantation and by spleen colony assays revealed that a significant fraction of HSCs and multipotent progenitors have multilineage potential at the single-cell level. These new insights prompt an erythroid-focused model of hematopoietic differentiation., Graphical Abstract, Highlights • RBCs are the predominant cell type produced by multipotent hematopoietic progenitors • All cell types with myeloid potential also produced RBCs and platelets in vivo • Single HSCs and MPPF cells are capable of multilineage hematopoietic reconstitution • Erythroid cell production emerges as a default hematopoietic fate, In this article, Forsberg and colleagues use quantitative reconstitution assays to demonstrate that all myeloid-competent progenitor cells also contribute to erythroid and platelet production. Single-cell in vivo analyses showed that hematopoietic stem cells and multipotent progenitors are clonally multipotent. These results suggest that erythropoiesis is a default hematopoietic fate and challenges current views on hematopoietic lineage potential and fate decisions.

Hematopoietic stem cells (HSCs) have the capacity to differentiate into vastly different types of mature blood cells. The epigenetic mechanisms regulating the multilineage ability, or multipotency of HSCs are not well understood. To test the hypothesis thatcisregulatory elements that control fate decisions for all lineages are primed in HSCs, we used ATAC-seq to compare chromatin accessibility of HSCs with five unipotent cell types. We observed the highest similarity in accessibility profiles between Megakaryocyte Progenitors and HSCs, whereas B cells had the greatest number of regions withde novogain in accessibility during differentiation. Despite these differences, we identifiedcisregulatory elements from all lineages that displayed epigenetic priming in HSCs. These findings provide new insights into the regulation of stem cell multipotency, as well as a resource to identify functional drivers of lineage fate.HIGHLIGHTSHSCs have higher global chromatin accessibility than any unilineage progenyMegakaryocyte Progenitors are the most closely related unipotent cell type to HSCsB cell commitment involvesde novochromatin accessibilityEvidence ofciselement priming of lineage-specific genes in HSCs

Platelets provide life-saving functions by halting external and internal bleeding. There is also a dark side to platelet biology, however. Recent reports provide evidence for increased platelet reactivity during aging of mice and humans, making platelets main suspects in the most prevalent aging-related human pathologies, including cardiovascular diseases, stroke, and cancer. What drives this platelet hyperreactivity during aging? Here, we discuss how hematopoietic stem cell differentiation pathways into the platelet lineage offer avenues to understand the fundamental differences between young and old platelets. Recent advances begin to unravel how the cellular and molecular regulation of the parent hematopoietic stem and progenitor cells likely imbue aging characteristics on the resulting Plt progeny. The resulting mechanistic insights into intrinsic platelet reactivity will provide strategies for selectively targeting age-related pathways. This brief viewpoint focuses on current concepts on aging hematopoiesis and the implications for platelet hyperactivity during aging.

Based on analyses of six individual interviews with young people from a sixth-grade school class, this study explores how young people talk about bullying and a particular bullying case in their class from various positions. Utilising thematic analysis, three themes were conceptualised as crucial in bullying: social status, powerful positions and fragile social positions. Symbolic interactionism, emphasising perspectives as constructed in interaction, were used to understand these social dynamics and bullying as a group phenomenon. The findings demonstrate the social landscape in which young people navigate, where social positions are in process but affected by their group norms.

Hematopoietic stem cell (HSC) trafficking is regulated by a number of complex mechanisms. Among them are the transmembrane protein Robo4 and the vascular cell adhesion molecule, VCAM1. Endothelial VCAM1 is a well-known regulator of hematopoietic cell trafficking, and our previous studies revealed that germline deletion of Robo4 led to impaired HSC trafficking, with an increase in vascular endothelial cell (VEC) numbers and downregulation of VCAM1 protein on sinusoidal VECs. Here, we utilized two Robo4 conditional deletion models in parallel with Robo4 germline knockout mice (R4KO) to evaluate the effects of acute and endothelial cell-specific Robo4 deletion on HSC trafficking. Strikingly similar to the R4KO, the acute deletion of Robo4 resulted in altered HSC distribution between the bone marrow and blood compartments, despite normal numbers of VECs and wild-type levels of VCAM1 cell surface protein on sinusoidal VECs. Additionally, consistent with the R4KO mice, acute loss of Robo4 in the host perturbed long-term engraftment of donor wild-type HSCs and improved HSC mobilization to the peripheral blood. These data demonstrate the significant role that endothelial Robo4 plays in directional HSC trafficking, independent of alterations in VEC numbers and VCAM1 expression.

Hematopoietic stem and progenitor cell (HSPC) transplantation is the paradigm for stem cell therapies. The protocol described here enables quantitative assessment of the body-wide HSPC reconstitution of different mature hematopoietic cells in mice based on their presence in circulating blood. The method determines donor-derived mature cell populations per mouse, over time, by quantitatively obtaining their absolute numbers in the peripheral blood and utilizing previously assessed tissue-distribution factors. A Markov-based birth/death computational model accounts for the drastic differences in mature cell half-lives. By quantifying the number of cells produced and eliminating host variability, the protocol can be used to directly compare the lineage output of different types of HSPCs on a per cell basis, thereby clarifying the lineage potential and expansion capacity of different cell populations. These protocols were developed for hematopoiesis, but can readily be extended to other contexts by simply replacing the cell types and distributions.HighlightsQuantitative assessment of stem and progenitor cell reconstitution capacityElimination of cell-specific recipient variability for accurate donor cell potentialDirectly comparable lineage output within and between stem and progenitor cellsBlood-based absolute quantification of whole-body repopulation over timeMarkov modelling-based consideration of differential mature cell half-lives

Respiratory diseases are a leading cause of death worldwide, with highly varied vulnerability to disease between individuals. The underlying reasons of disease susceptibility are unknown, but often include a variable immune response in lungs. Recently, we identified a surprising novel role of the interleukin 7 receptor (IL7R), a primarily lymphoid-associated regulator, in fetal-specified, lung-resident macrophage development. Here, we report that traditional, hematopoietic stem cell-derived myeloid cells in the adult lung, peripheral blood, and bone marrow also depend on IL7R expression. Using single and double germline knockout models, we found that eosinophil numbers were reduced upon deletion of IL7Rα. We then employed two Cre recombinase models in lineage tracing experiments to test whether these cells developed through an IL7Rα+ pathway. Despite the impact of IL7Rα deletion, IL7R-Cre labeled only a minimal fraction of eosinophils. We therefore examined the intrinsic versus extrinsic requirement for IL7R in the production of eosinophils using reciprocal hematopoietic stem cell transplantation assays. These assays revealed that extrinsic, but not eosinophil-intrinsic, IL7R is required for eosinophil reconstitution by HSCs in the adult lung. To determine which external factors may be influencing eosinophil development and survival, we performed a cytokine array analysis between wild-type and IL7Rα-deficient mice and found several differentially regulated proteins. These findings expand upon our previous publication that IL7R is required not only for proper lymphoid cell development and homeostasis, but also for myeloid cell homeostasis in tissues.

Respiratory diseases are a leading cause of death worldwide, with highly varied vulnerability to disease between individuals. The underlying reasons of disease susceptibility are unknown, but often include a variable immune response in lungs. Recently, we identified a surprising novel role of the interleukin 7 receptor (IL7R), a primarily lymphoid-associated regulator, in fetal-specified, lung-resident macrophage development. Here, we report that traditional, hematopoietic stem cell-derived myeloid cells in the adult lung, peripheral blood, and bone marrow also depend on IL7R expression. Using single and double germline knockout models, we found that eosinophil numbers were reduced upon deletion of IL7Rα. We then employed two Cre recombinase models in lineage tracing experiments to test whether these cells developed through an IL7Rα+ pathway. Despite the impact of IL7Rα deletion, IL7R-Cre labeled only a minimal fraction of eosinophils. We therefore examined the intrinsic versus extrinsic requirement for IL7R in the production of eosinophils using reciprocal hematopoietic stem cell transplantation assays. These assays revealed that extrinsic, but not eosinophil-intrinsic, IL7R is required for eosinophil reconstitution by HSCs in the adult lung. To determine which external factors may be influencing eosinophil development and survival, we performed a cytokine array analysis between wild-type and IL7Rα-deficient mice and found several differentially regulated proteins. These findings expand upon our previous publication that IL7R is required not only for proper lymphoid cell development and homeostasis, but also for myeloid cell homeostasis in tissues.HighlightsLoss of IL7Rα resulted in significantly fewer eosinophils in adult miceIL7R-Cre lineage tracing revealed minimal labeling of eosinophilsIL7Rα-deficient HSCs robustly reconstituted eosinophils in a WT hostWT HSCs failed to fully reconstitute eosinophils in IL7Rα-/- hostsSeveral cytokines are differentially expressed in WT and IL7Rα-deficient mice

In this study, we draw on Erving Goffman’s work on the presentation of self to explore responses by 12–15-year-old (i.e. 6th–9th grade) school students to an open-ended survey question about why they think they were bullied. In doing so, we contribute to a relatively unexplored aspect of school bullying research by focussing on how those students who are subjected to bullying understand their own bullying experiences. We focus in particular on explanations that focus on themselves as individuals. Utilising thematic analysis, we identified six themes: (1) Body, (2) Manner, (3) Social structures, (4) Opinions and interests, (5) Ability, and (6) Relations. Our analysis of the students’ responses suggests that they were bullied because they were perceived as different in some sense, and that such understandings of difference are connected to broader social and societal norms. These findings have important implications for understandings of bullying as aggressive acts and suggest that rather than simply focussing on the negative behaviour of individuals, anti-bullying initiatives also need to focus on the social structures that underpin the understandings of difference that facilitate such behaviour.