Ezh2 is essential for the generation of functional yolk sac derived erythro-myeloid progenitors

Hematopoietic cluster formation: an essential prelude to blood cell genesis

Adult blood cells are produced in the bone marrow by hematopoietic stem cells (HSCs), the origin of which can be traced back to fetal developmental stages. Indeed, during mouse development, at days 10-11 of gestation, the aorta-gonad-mesonephros (AGM) region is a primary site of HSC production, with characteristic cell clusters related to stem cell genesis observed in the dorsal aorta. Similar clusters linked with hematopoiesis are also observed in the other sites such as the yolk sac and placenta. In this review, I outline the formation and function of these clusters, focusing on the well-characterized intra-aortic hematopoietic clusters (IAHCs).

Fosl2 Deficiency Predisposes Mice to Osteopetrosis, Leading to Bone Marrow Failure

Arthritis causes Fos-like 2 (Fosl2) inactivation, and various immune cells contribute to its pathogenesis. However, little is known about the role of Fosl2 in hematopoiesis and the possible pathological role of Fosl2 inactivation in the hematopoietic system in arthritis. In this study, we show that Fosl2 maintains hematopoietic stem cell (HSC) quiescence and differentiation while controlling the inflammatory response via macrophages. Fosl2-specific deletion in the hematopoietic system caused the expansion of HSCs and myeloid cell growth while affecting erythroid and B cell differentiation. Fosl2 inactivation enhanced macrophage M1 polarization and stimulated proinflammatory cytokines and myeloid growth factors, skewing HSCs toward myeloid cell differentiation, similar to hematopoietic alterations in arthritic mice. Loss of Fosl2 mediated by Vav-iCre also displays an unexpected deletion in embryonic erythro-myeloid progenitor-derived osteoclasts, leading to osteopetrosis and anemia. The reduced bone marrow cellularity in Vav-iCreFosl2f/f mice is a consequence of the reduced bone marrow space in osteopetrotic mice rather than a direct role of Fosl2 in hematopoiesis. Thus, Fosl2 is indispensable for erythro-myeloid progenitor-derived osteoclasts to maintain the medullary cavity to ensure normal hematopoiesis. These findings improve our understanding of the pathogenesis of bone-destructive diseases and provide important implications for developing therapeutic approaches for these diseases.

Development of the hematopoietic system: expanding the concept of hematopoietic stem cell-independent hematopoiesis

Hematopoietic stem cells (HSCs) give rise to nearly all blood cell types and play a central role in blood cell production in adulthood. For many years it was assumed that these roles were similarly responsible for driving the formation of the hematopoietic system during the embryonic period. However, detailed analysis of embryonic hematopoiesis has revealed the presence of hematopoietic cells that develop independently of HSCs both before and after HSC generation. Furthermore, it is becoming increasingly clear that HSCs are less involved in the production of functioning blood cells during the embryonic period when there is a much higher contribution from HSC-independent hematopoietic processes. We outline the current understanding and arguments for HSC-dependent and -independent hematopoiesis, mainly focusing on mouse ontogeny.

Haematopoietic development and HSC formation in vitro: promise and limitations of gastruloid models

Haematopoietic stem cells (HSCs) are the most extensively studied adult stem cells. Yet, six decades after their first description, reproducible and translatable generation of HSC in vitro remains an unmet challenge. HSC production in vitro is confounded by the multi-stage nature of blood production during development. Specification of HSC is a late event in embryonic blood production and depends on physical and chemical cues which remain incompletely characterised. The precise molecular composition of the HSC themselves is incompletely understood, limiting approaches to track their origin in situ in the appropriate cellular, chemical and mechanical context. Embryonic material at the point of HSC emergence is limiting, highlighting the need for an in vitro model of embryonic haematopoietic development in which current knowledge gaps can be addressed and exploited to enable HSC production. Gastruloids are pluripotent stem cell-derived 3-dimensional (3D) cellular aggregates which recapitulate developmental events in gastrulation and early organogenesis with spatial and temporal precision. Gastruloids self-organise multi-tissue structures upon minimal and controlled external cues, and are amenable to live imaging, screening, scaling and physicochemical manipulation to understand and translate tissue formation. In this review, we consider the haematopoietic potential of gastruloids and review early strategies to enhance blood progenitor and HSC production. We highlight possible strategies to achieve HSC production from gastruloids, and discuss the potential of gastruloid systems in illuminating current knowledge gaps in HSC specification.

Engineered hematopoietic and immune cells derived from human pluripotent stem cells

For the past decade, significant advances have been achieved in human hematopoietic stem cell (HSC) transplantation for treating various blood diseases and cancers. However, challenges remain with the quality control, amount, and cost of HSCs and HSC-derived immune cells. The advent of human pluripotent stem cells (hPSCs) may transform HSC transplantation and cancer immunotherapy by providing a cost-effective and scalable cell source for fundamental studies and translational applications. In this review, we discuss the current developments in the field of stem cell engineering for hematopoietic stem and progenitor cell (HSPC) differentiation and further differentiation of HSPCs into functional immune cells. The key advances in stem cell engineering include the generation of HSPCs from hPSCs, genetic modification of hPSCs, and hPSC-derived HSPCs for improved function, further differentiation of HPSCs into functional immune cells, and applications of cell culture platforms for hematopoietic cell manufacturing. Current challenges impeding the translation of hPSC-HSPCs and immune cells as well as further directions to address these challenges are also discussed.

The CUT&RUN suspect list of problematic regions of the genome

BACKGROUND

Cleavage Under Targets and Release Using Nuclease (CUT&RUN) is an increasingly popular technique to map genome-wide binding profiles of histone modifications, transcription factors, and co-factors. The ENCODE project and others have compiled blacklists for ChIP-seq which have been widely adopted: these lists contain regions of high and unstructured signal, regardless of cell type or protein target, indicating that these are false positives. While CUT&RUN obtains similar results to ChIP-seq, its biochemistry and subsequent data analyses are different. We found that this results in a CUT&RUN-specific set of undesired high-signal regions.

RESULTS

We compile suspect lists based on CUT&RUN data for the human and mouse genomes, identifying regions consistently called as peaks in negative controls. Using published CUT&RUN data from our and other labs, we show that the CUT&RUN suspect regions can persist even when peak calling is performed with SEACR or MACS2 against a negative control and after ENCODE blacklist removal. Moreover, we experimentally validate the CUT&RUN suspect lists by performing reiterative negative control experiments in which no specific protein is targeted, showing that they capture more than 80% of the peaks identified.

CONCLUSIONS

We propose that removing these problematic regions can substantially improve peak calling in CUT&RUN experiments, resulting in more reliable datasets.

Translational Comparison of the Human and Mouse Yolk Sac Development and Function

The yolk sac (YS) is the oldest of the extraembryonic membranes in vertebrates. Considered a transitory structure in the human species, the importance of the YS for a successful pregnancy is often overlooked. Due to the general inaccessibility of healthy human YS tissue for research, the use of experimental animal models is of great value. In order to better understand whether the mouse could be used as a translational model for the study of the human YS under normal and pathological conditions, this review comprehensively describes key developmental aspects of the human and mouse YS, detailing their development and function. YS major similarities in both species comprise the following: (1) histological composition (both being composed of endoderm, mesoderm, and mesothelium layers); (2) endoderm endocytosis, synthesis, secretion, and transport capabilities; and (3) mesoderm onset of haematopoiesis and angiogenesis. Examples of main dissimilarities include (1) persistence across pregnancy (i.e. early pregnancy in humans vs term pregnancy in mice); (2) the existence of a secondary YS in humans; (3) the presence of proliferative primordial germ cells (PGCs) in the human versus their absence in mice; and (4) eversion of histological layers in the mouse. Although these differences should be considered when interpreting data from mouse-based studies, the overall morphofunctional similarities in the YS between these species indicate that the mouse can be potentially used as a translational model for the study of the human YS.