B-lymphoid potential in pre-liver mouse embryo

Assessing Work-Family Conflict Experienced by Chinese Parents of Young Children: Validation of the Chinese Version of the Work and Family Conflict Scale

While there a number of measures to assess work-family conflict already exist, there are no well-validated measures exist for clinical use with Chinese parents. This study sought to validate a Chinese version of the work and family conflict scale (WAFCS), a brief 10-item scale developed for clinical and research use with parents. Relying on a sample of 447 Chinese parents in Hong Kong, this study examined the psychometric properties of the Chinese version of the WAFCS. Results showed that a two-factor model, similar to that of the original scale, fit the data well. The scale had concurrent and discriminant validity, while the scale's measurement invariance across gender and its internal consistency were also supported. Such robust psychometric properties suggest that the WAFCS is a promising tool that can be applied in a variety of research and clinical settings to examine work-family conflict experienced by Chinese parents.

Pro-inflammatory Aorta-Associated Macrophages Are Involved in Embryonic Development of Hematopoietic Stem Cells

Hematopoietic stem cells (HSCs) are generated from specialized endothelial cells of the embryonic aorta. Inflammatory factors are implicated in regulating mouse HSC development, but which cells in the aorta-gonad-mesonephros (AGM) microenvironment produce these factors is unknown. In the adult, macrophages play both pro- and anti-inflammatory roles. We sought to examine whether macrophages or other hematopoietic cells found in the embryo prior to HSC generation were involved in the AGM HSC-generative microenvironment. CyTOF analysis of CD45⁺ AGM cells revealed predominance of two hematopoietic cell types, mannose-receptor positive macrophages and mannose-receptor negative myeloid cells. We show here that macrophage appearance in the AGM was dependent on the chemokine receptor Cx3cr1. These macrophages expressed a pro-inflammatory signature, localized to the aorta, and dynamically interacted with nascent and emerging intra-aortic hematopoietic cells (IAHCs). Importantly, upon macrophage depletion, no adult-repopulating HSCs were detected, thus implicating a role for pro-inflammatory AGM-associated macrophages in regulating the development of HSCs.

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Yolk-sac-derived macrophages are the most abundant hematopoietic cells in the AGM

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Cx3cr1 mediates yolk-sac macrophage progenitor recruitment to the AGM niche

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AGM macrophages dynamically interact with emerging intra-aortic hematopoietic cells

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Pro-inflammatory AGM macrophages are positive regulators of HSC generation

Many layers of embryonic hematopoiesis: new insights into B-cell ontogeny and the origin of hematopoietic stem cells

In adult hematopoiesis, the hematopoietic stem cell (HSC) sits at the top of a hierarchy of hematopoietic progenitors responsible for generating the diverse repertoire of blood and immune cells. During embryonic development, however, the initial waves of hematopoiesis provide the first functioning blood cells of the developing embryo, such as primitive erythrocytes arising in the yolk sac, independently of HSCs. In the field of developmental immunology, it has been recognized that some components of the immune system, such as B-1a lymphocytes, are uniquely produced during the embryonic and neonatal period, suggesting a "layered" development of immunity. Several recent studies have shed new light on the developmental origin of the layered immune system, suggesting complex and sometimes multiple contributions to unique populations of innate-like immune cells from both fetal HSCs and earlier HSC-independent progenitors. In this review, we will attempt to synthesize these studies to provide an integrated model of developmental hematopoiesis and layered immunity that may offer new insights into the origin of HSCs.

B-1 B cell development in the fetus and adult

Models of hematopoiesis often depict lymphocyte production as a uniform process in which a homogenous population of hematopoietic stem cells (HSCs) generates progenitors from which all types of lymphocytes are derived. However, it is increasingly evident that these schemes are too simplistic and that the lymphoid potential of HSCs and precursors arising in the embryo, fetus, neonate, and adult is remarkably distinct. We review recent findings regarding the development of B lymphocytes, and the B-1 B cell lineage in particular, as a case in point. These studies show that B-1 and B-2 B cells involved in innate and adaptive immune responses, respectively, arise in staggered waves of development from distinct progenitors. We discuss the implications of this layered model of B cell development for understanding normal and dysregulated B lymphopoiesis.

Unique Properties of Fetal Lymphoid Progenitors Identified According to RAG1 Gene Expression

RAG1/GFP knockin mice were exploited to isolate and characterize fetal lymphoid progenitors. CD11b and IL-7Ralpha are expressed in a developmental stage-dependent fashion, revealing how substantial numbers of early lymphoid progenitors were discarded or neglected in previous studies. The myeloerythroid potential of fetal progenitors in clonal assays declined in synchrony with activation of the RAG1 locus but was not completely extinguished. Lymphoid differentiation corresponded to patterns of gene expression previously found for adult marrow, but no fraction of fetal liver was enriched with respect to B + T progenitors. Also, unlike adults, fetal lymphoid progenitors transiently expressed endothelial cell markers. These findings help to reconcile discrepancies in previous reports and suggest that the fetal immune system arises via unique mechanisms.

Hematopoietic stem cells and their precursors: developmental diversity and lineage relationships

Within the context of the developing embryo, restrictions in cell lineage potential occur through cell-cell interactions and signaling molecules, leading to changes in genetic programs and to the emergence of disparate tissues containing functionally distinct cell types including somatic stem cells. Tissue maintenance in the adult is thought to occur through specific stem cells, and in the case of the hematopoietic system, through hematopoietic stem cells (HSCs). These cells arise in midgestation within the region of the embryo containing the dorsal aorta, gonads, and mesonephros (AGM) and are thought to maintain a distinct hematopoietic lineage-restricted fate. However, recent transplantation experiments suggest that within the adult, HSCs previously thought to be restricted can, under certain circumstances, display unexpected lineage potentials. With these surprising and controversial results, it is becoming apparent that a better understanding of the developmental processes, molecular programs and lineage relationships leading to the emergence of adult stem cells will provide insight into the incremental steps involved in lineage determination, and perhaps possibilities for the manipulated differentiation of stem cells. The most widely studied, accessible stem cell and cellular differentiation hierarchy is that of the hematopoietic system. With the issue of stem cell potential in the forefront, the focus of this review is on the development of the hematopoietic system: how HSCs arise in the embryo, the lineage relationships of hematopoietic cells as they are generated, and the identification of precursor cells fated to the hematopoietic lineage throughout ontogeny.

Expression of 4-Integrin Defines the Earliest Precursor of Hematopoietic Cell Lineage Diverged From Endothelial Cells

Embryonic stem cells can differentiate in vitro into hematopoietic cells through two intermediate stages; the first being FLK1+ E-cadherin− proximal lateral mesoderm and the second being CD45− VE-cadherin+endothelial cells. To further dissect the CD45−VE-cadherin+ cells, we have examined distribution of 4-integrin on this cell population, because 4-integrin is the molecule expressed on hematopoietic stem cells. During culture of FLK1+ E-cadherin− cells, CD45− VE-cadherin+4-integrin− cells differentiate first, followed by 4-integrin+ cells appearing in both CD45− VE-cadherin+ and CD45−VE-cadherin− cell populations. In the CD45−VE-cadherin+ cell population, 4-integrin+ subset but not 4-integrin− subset had the potential to differentiate to hematopoietic lineage cells, whereas endothelial cell progenitors were present in both subsets. The CD45−VE-cadherin− 4-integrin+ cells also showed hematopoietic potential. Reverse transcription-polymerase chain reaction analyses showed that differential expression of the Gata2 and Myb genes correlated with the potential of the 4-integrin+ cells to give rise to hematopoietic cell differentiation. Hematopoietic CD45−VE-cadherin+ 4-integrin+ cells were also present in the yolk sac and embryonic body proper of 9.5 day postcoitum mouse embryos. Our results suggest that the expression of 4-integrin is a marker of the earliest precursor of hematopoietic cell lineage that was diverged from endothelial progenitors.

Expression of 4-Integrin Defines the Earliest Precursor of Hematopoietic Cell Lineage Diverged From Endothelial Cells

Embryonic stem cells can differentiate in vitro into hematopoietic cells through two intermediate stages; the first being FLK1+ E-cadherin− proximal lateral mesoderm and the second being CD45− VE-cadherin+endothelial cells. To further dissect the CD45−VE-cadherin+ cells, we have examined distribution of 4-integrin on this cell population, because 4-integrin is the molecule expressed on hematopoietic stem cells. During culture of FLK1+ E-cadherin− cells, CD45− VE-cadherin+4-integrin− cells differentiate first, followed by 4-integrin+ cells appearing in both CD45− VE-cadherin+ and CD45−VE-cadherin− cell populations. In the CD45−VE-cadherin+ cell population, 4-integrin+ subset but not 4-integrin− subset had the potential to differentiate to hematopoietic lineage cells, whereas endothelial cell progenitors were present in both subsets. The CD45−VE-cadherin− 4-integrin+ cells also showed hematopoietic potential. Reverse transcription-polymerase chain reaction analyses showed that differential expression of the Gata2 and Myb genes correlated with the potential of the 4-integrin+ cells to give rise to hematopoietic cell differentiation. Hematopoietic CD45−VE-cadherin+ 4-integrin+ cells were also present in the yolk sac and embryonic body proper of 9.5 day postcoitum mouse embryos. Our results suggest that the expression of 4-integrin is a marker of the earliest precursor of hematopoietic cell lineage that was diverged from endothelial progenitors.

Antigenic profiles of endothelial and hemopoietic lineages in murine intraembryonic hemogenic sites

Two hemogenic sites are present in mouse embryos before the onset of fetal liver hemopoiesis. While the yolk sac provides for immediate erythropoiesis, an intraembryonic region encompassing the dorsal aorta produces definitive hematopoietic stem cells, as shown experimentally. At early developmental stages this region, that we named paraaortic splanchnopleura, produces multipotent progenitors. At the time of fetal liver colonisation, the paraaortic splanchnopleura further evolves into aorta, gonads and mesonephros (AGM) and contains progenitors capable of long term multilineage reconstitution. Only then are cytologically identifiable collections of early hemopoietic cells present in various arteries and in the mesentery. The present report focuses on the antigenic characterisation of immature hemopoietic progenitors in order to trace back the intraembryonic precursors at earlier developmental stages. CD34, an antigen expressed by immature progenitors and endothelial cells, labels all potential hemopoietic sites. Markers, supposed to counterstain endothelial cells and spare CD34+ hemopoietic cells, also stain various hemopoietic cells. The meaning of these shared antigenic expressions between cells of the endothelial and hemopoietic lineages in the early embryo is discussed.

B cell development in mice

The development and establishment of the B Cell Repertoire is the net result of both genetic and environmental forces. The primary event at the genetic level is Ig gene rearrangement resulting in numerous possible combination of genes which can be further modified by somatic events such as N segment addition and somatic mutation. Environmental forces in the form of self and exogenous Ags also shape the repertoire by positively or negatively selecting B cells according to the specificity of their Ig receptors. These are dynamic processes beginning with the earliest expression of immunoglobulins in fetal life and continuing throughout life. In this review we discuss the genetic and selective mechanisms responsible for differences in the early immune system compared to that of the adult.

Lymphoid potential, probed before circulation in mouse, is restricted to caudal intraembryonic splanchnopleura

Emergence of hemopoietic stem cells in the mammalian embryo has yet to be definitively allocated. Previously, we detected multipotent hemopoietic precursors in the region surrounding the dorsal aorta (paraaortic splanchnopleura) beginning at 8.5 days postcoitum (dpc). However, as circulation is already established, it remained unclear whether hemopoietic precursors arise in situ or are blood-delivered. By adding an organotypic step to our former culture system, we now detect lymphocyte and multipotent myeloid precursors from the intraembryonic splanchnopleura as early as 7.5 dpc. Under identical conditions, yolk sacs from the same embryos are unable to generate lymphoid progeny and have a reduced potential for myeloid differentiation and maintenance. Thus, if isolated before circulation, the yolk sac does not produce multipotent precursors and therefore does not contribute to definitive hemopoiesis in the mouse.