Developmental regulation of endothelial-to-hematopoietic transition from induced pluripotent stem cells.

Hematopoietic stem cells (HSCs) arise in embryogenesis from a specialized hemogenic endothelium (HE). In this process, HE cells undergo a unique fate change termed endothelial-to-hematopoietic transition, or EHT. While induced pluripotent stem cells (iPSCs) give rise to HE with robust hemogenic potential, the generation of bona fide HSCs from iPSCs remains a challenge.

p65 signaling dynamics drive the developmental progression of hematopoietic stem and progenitor cells through cell cycle regulation.

Most gene functions have been discovered through phenotypic observations under loss of function experiments that lack temporal control. However, cell signaling relies on limited transcriptional effectors, having to be re-used temporally and spatially within the organism. Despite that, the dynamic nature of signaling pathways have been overlooked due to the difficulty on their assessment, resulting in important bottlenecks.

Nod1-dependent NF-kB activation initiates hematopoietic stem cell specification in response to small Rho GTPases.

Uncovering the mechanisms regulating hematopoietic specification not only would overcome current limitations related to hematopoietic stem and progenitor cell (HSPC) transplantation, but also advance cellular immunotherapies. However, generating functional human induced pluripotent stem cell (hiPSC)-derived HSPCs and their derivatives has been elusive, necessitating a better understanding of the developmental mechanisms that trigger HSPC specification. Here, we reveal that early activation of the Nod1-Ripk2-NF-kB inflammatory pathway in endothelial cells (ECs) primes them to switch fate towards definitive hemogenic endothelium, a pre-requisite to specify HSPCs.

Identification of Transcription Factor Binding Sites by Cleavage Under Target and Release Using Nuclease in Zebrafish.

Cleavage Under Targets and Release Using Nuclease (CUT&RUN) has emerged as a chromatin profiling strategy that excels traditional methods. Although CUT&RUN has been widely utilized in mammalian cells, its use in the zebrafish is at its early stages. In this study, we have developed a protocol to successfully perform CUT&RUN to map transcription factor (TF) binding sites in embryonic, adult tissues, and FACS-sorted zebrafish cells.

A zebrafish model of granulin deficiency reveals essential roles in myeloid cell differentiation.

Granulin is a pleiotropic protein involved in inflammation, wound healing, neurodegenerative disease, and tumorigenesis. These roles in human health have prompted research efforts to use granulin to treat rheumatoid arthritis and frontotemporal dementia and to enhance wound healing. But how granulin contributes to each of these diverse biological functions remains largely unknown.

Proinflammatory Signals as Fuel for the Fire of Hematopoietic Stem Cell Emergence.

Hematopoietic stem cells (HSCs) have the extraordinary ability to both self-renew and generate all mature blood cell lineages. The ability to produce or expand patient-derived HSCs in vitro would greatly improve the outcome for patients with blood disorders that are currently treated with allogeneic HSC transplantation. Many laboratories have been working to identify the signals required for HSC emergence in their native environments to apply this knowledge in vitro.

Wnt9a Is Required for the Aortic Amplification of Nascent Hematopoietic Stem Cells.

All mature blood cell types in the adult animal arise from hematopoietic stem and progenitor cells (HSPCs). However, the developmental cues regulating HSPC ontogeny are incompletely understood. In particular, the details surrounding a requirement for Wnt/β-catenin signaling in the development of mature HSPCs are controversial and difficult to consolidate.

TNFα Impairs Rhabdoviral Clearance by Inhibiting the Host Autophagic Antiviral Response.

TNFα is a pleiotropic pro-inflammatory cytokine with a key role in the activation of the immune system to fight viral infections. Despite its antiviral role, a few viruses might utilize the host produced TNFα to their benefit. Some recent reports have shown that anti-TNFα therapies could be utilized to treat certain viral infections.

The NF-κB family: Key players during embryonic development and HSC emergence.

The nuclear factor-κB (NF-κB) family is a crucial transcription factor group known mainly for its role in the regulation of the immune system and its response to infection in vertebrates. The signaling pathway leading to NF-κB activation and translocation to the nucleus to exert its function as a transcription factor is well conserved among Kingdom Animalia, which has helped to elucidate other roles that NF-κB plays in other biological contexts such as developmental biology. The manipulation of NF-κB members in a diverse range of animal models results in severe developmental defects during embryogenesis, very often leading to embryonic lethality.

Gata2b is a restricted early regulator of hemogenic endothelium in the zebrafish embryo.

The adult blood system is established by hematopoietic stem cells (HSCs), which arise during development from an endothelial-to-hematopoietic transition of cells comprising the floor of the dorsal aorta. Expression of aortic runx1 has served as an early marker of HSC commitment in the zebrafish embryo, but recent studies have suggested that HSC specification begins during the convergence of posterior lateral plate mesoderm (PLM), well before aorta formation and runx1 transcription. Further understanding of the earliest stages of HSC specification necessitates an earlier marker of hemogenic endothelium.

Md1 and Rp105 regulate innate immunity and viral resistance in zebrafish.

TLR4 was the first TLR family member identified in mammals and is responsible for the activation of the immune response by bacterial LPS. Later, MD1 and RP105 were shown to form complexes that directly interact with the MD2-TLR4 complex, acting as physiological negative regulators of LPS signaling. Despite the general conservation of various TLR families from fish to mammals, several differences can be appreciated, such as the high tolerance of fish to LPS, the absence of the crucial accessory molecules Md2 and Cd14 for Tlr4 signaling in fish, the absence of Tlr4 in some fish species, and the confirmation that LPS does not signal through Tlr4 in zebrafish.

Proinflammatory signaling regulates hematopoietic stem cell emergence.

Hematopoietic stem cells (HSCs) underlie the production of blood and immune cells for the lifetime of an organism. In vertebrate embryos, HSCs arise from the unique transdifferentiation of hemogenic endothelium comprising the floor of the dorsal aorta during a brief developmental window. To date, this process has not been replicated in vitro from pluripotent precursors, partly because the full complement of required signaling inputs remains to be determined.

Tnfa signaling through tnfr2 protects skin against oxidative stress-induced inflammation.

TNFα overexpression has been associated with several chronic inflammatory diseases, including psoriasis, lichen planus, rheumatoid arthritis, and inflammatory bowel disease. Paradoxically, numerous studies have reported new-onset psoriasis and lichen planus following TNFα antagonist therapy. Here, we show that genetic inhibition of Tnfa and Tnfr2 in zebrafish results in the mobilization of neutrophils to the skin.

The zebrafish granulocyte colony-stimulating factors (Gcsfs): 2 paralogous cytokines and their roles in hematopoietic development and maintenance.

Granulocyte colony-stimulating factor (Gcsf) drives the proliferation and differentiation of granulocytes, monocytes, and macrophages (mφs) from hematopoietic stem and progenitor cells (HSPCs). Analysis of the zebrafish genome indicates the presence of 2 Gcsf ligands, likely resulting from a duplication event in teleost evolution. Although Gcsfa and Gcsfb share low sequence conservation, they share significant similarity in their predicted ligand/receptor interaction sites and structure.