Biology subjects

Speck, N. A.

Publications and source records attributed to Speck, N. A..

9 recordsLinked to original sources

bioRxiv2026

In situ identification of pre-hematopoietic stem cells and their niche

Definitive hematopoietic stem cells (HSCs) emerge predominantly along the ventral surface of the dorsal aorta in the embryonic aorta-gonad-mesonephros (AGM) region, yet the spatial organization of the niche underlying this developmental asymmetry remains poorly understood. Defining the native niche of pre-HSCs has also been hindered by their rarity, transient nature and lack of a single definitive marker for their identification in situ. Here, we integrated single-cell and spatial transcriptomics to construct a spatiotemporal atlas of the niche in the AGM. Neural cells and chondrogenic mesenchyme predominated dorsally, whereas N-cadherin mesenchymal stromal cells (N-cad+ MSCs) formed a ventral layer between the aortic endothelium and mesonephric cells. BMP and SHH signaling showed overall dorsal enrichment, whereas WNT, NOTCH and KIT signaling were enriched ventrally, with these cellular and signaling patterns dynamically remodeled across HSC ontogeny. Imaging-based spatial transcriptomics validated the findings and further enabled the identification of individual pre-HSCs in situ and revealed a multicellular niche comprising endothelial cells, N-cad+ MSCs, intra-aortic hematopoietic cluster cells and macrophages. TGF{beta} and NOTCH signals were primarily supplied locally, whereas major sources of BMP and WNT were more distant. Functional perturbation identified niche-derived CD200 as an immune-regulatory signal promoting HSC development, validating a spatially predicted niche interaction. Together, our findings link tissue-scale spatial organization with the local multicellular niche supporting the preferential development of HSCs along the ventral aorta.

developmental biology↗

bioRxiv2025

Human length telomeres restrict the regenerative potential of hematopoietic stem cells in mice

Extremely short telomeres cause bone marrow failure in telomere biology disorder (TBDs) patients. Here, we employed the recently developed Telomouse with human-length telomeres resulting from a single amino acid substitution in the helicase Rtel1 (Rtel1M492K/M492K) to determine the effects of the short telomeres on the bone marrow and hematopoiesis. Under homeostatic conditions, Telomice have notably short telomeres but normal hematopoiesis. However, when forced to repopulate following repeated treatment with 5-fluoro-uracil or upon bone marrow transplantation into lethally irradiated mice, bone marrow progenitor cells are significantly depleted in Telomice compared to wild-type controls. This effect is associated with increased frequency of telomere repeat arrays too short to be detected by fluorescence in situ hybridization in the bone marrow of Telomice.

genetics↗

bioRxiv2025

Restraint of TGFβ family signaling by SMAD7 is necessary for hematopoietic stem cell maturation in the embryo.

Hematopoietic stem cells (HSCs), defined as cells that can engraft an adult when transplanted, mature from precursors (pre-HSCs) that differentiate from hemogenic endothelial cells (HECs) in the embryo. Many signaling pathways required to generate the first hematopoietic stem and progenitor cells in the embryo are well-characterized, but how HSCs mature from pre-HSCs is poorly understood. Here we show that "mothers against decapentaplegic homolog 7" (SMAD7), a negative regulator of transforming growth factor beta (TGF{beta}) and bone morphogenetic protein (BMP) signaling, is required for pre-HSC to HSC maturation. Deletion of Smad7 in endothelial cells allows the formation of pre-HSCs from HECs but impairs their maturation into HSCs. The data indicate that although TGF{beta} and BMP signaling are required for the generation of HECs and for HECs to undergo an endothelial-to-hematopoietic transition to generate pre-HSCs, one or both pathways must be subsequently down-regulated for effective pre-HSC to HSC maturation.

developmental biology↗

bioRxiv2025

E2f coordinates the cell cycle and cell fate of hematopoietic progenitors to drive stress myelopoiesis

During inflammation, cytokines such as Tnf, Il1{beta} and Il6 stimulate hematopoietic stem and progenitor cells (HSPCs) to proliferate and accelerate the production of inflammatory cells from the myeloid lineage through a process called stress myelopoiesis. Genetic inactivation of repressors of cell cycle activity in HSPCs is sufficient to recapitulate stress myelopoiesis, suggesting that the cell cycle activity and cell fate decision of proliferative HSPCs are coordinated by a cell intrinsic mechanism. However, the nature of this mechanism remains unknown. Here, we show that E2f simultaneously regulates proliferation of HSPCs, repression of alternative cell fates via the activation of Suz12/Ezh2-containing PRC2 complex and promotion of the myeloid fate by enhancing the signaling activity of CD131, the common {beta}chain receptor for {beta}cytokines (i.e. Il3 and Gm-Csf). Accordingly, dual inhibition of Ezh2 and {beta}cytokine signaling activity in a preclinical model of colitis represses stress myelopoiesis and restores colon homeostasis. Our results suggest that dual targeting of {beta}cytokine signaling and Ezh2 activity represents a novel therapeutic strategy to repress the production of pro-inflammatory myeloid cells in a wide spectrum of inflammatory diseases.

cell biology↗

bioRxiv2023

Tropomyosin 1 deficiency facilitates cell state transitions and enhances hemogenic endothelial cell specification during hematopoiesis

Tropomyosins coat actin filaments and impact actin-related signaling and cell morphogenesis. Genome-wide association studies have linked Tropomyosin 1 (TPM1) with human blood trait variation. Prior work suggested that TPM1 regulated blood cell formation in vitro, but it was unclear how or when TPM1 affected hematopoiesis. Using gene-edited induced pluripotent stem cell (iPSC) model systems, TPM1 knockout was found to augment developmental cell state transitions, as well as TNF and GTPase signaling pathways, to promote hemogenic endothelial (HE) cell specification and hematopoietic progenitor cell (HPC) production. Single-cell analyses showed decreased TPM1 expression during human HE specification, suggesting that TPM1 regulated in vivo hematopoiesis via similar mechanisms. Indeed, analyses of a TPM1 gene trap mouse model showed that TPM1 deficiency enhanced the formation of HE during embryogenesis. These findings illuminate novel effects of TPM1 on developmental hematopoiesis.

cell biology↗

bioRxiv2023

RUNX1 is required in granulocyte-monocyte progenitors to attenuate inflammatory cytokine production by neutrophils

The transcription factor RUNX1 is mutated in familial platelet disorder with associated myeloid malignancies (FPDMM) and in sporadic myelodysplastic syndrome and leukemia. RUNX1 regulates inflammation in multiple cell types. Here we show that RUNX1 is required in granulocyte-monocyte progenitors (GMPs) to restrict the inflammatory response of neutrophils to toll-like receptor 4 (TLR4) signaling. Loss of RUNX1 in GMPs increased the TLR4 coreceptor CD14 on neutrophils, which contributed to neutrophils increased inflammatory cytokine production in response to the TLR4 ligand lipopolysaccharide. RUNX1 loss increased the chromatin accessibility of retrotransposons in GMPs and neutrophils and induced a type I interferon signature characterized by enriched footprints for signal transducer and activator of transcription (STAT1::STAT2) and interferon regulatory factors (IRF) in opened chromatin, and increased expression of interferon-stimulated genes. The overproduction of inflammatory cytokines by neutrophils was reversed by inhibitors of type I IFN signaling. We conclude that RUNX1 restrains the chromatin accessibility of retrotransposons in GMPs and neutrophils, and that loss of RUNX1 increases proinflammatory cytokine production by elevating tonic type I interferon signaling.

developmental biology↗

bioRxiv2021

MyD88-dependent TLR signaling oppositely regulates hematopoietic progenitor and stem cell formation in the embryo

Hemogenic endothelial (HE) cells in the dorsal aorta undergo an endothelial to hematopoietic transition (EHT) to form lympho-myeloid biased progenitors (LMPs), pre-hematopoietic stem cells (pre-HSCs) and adult-repopulating HSCs. These briefly accumulate in intra-arterial hematopoietic clusters (IAHCs) before being released into the circulation. It is generally assumed that the number of IAHC cells correlates with the number of HSCs. Here we show that changes in the number of IAHC cells, LMPs, and HSCs can be uncoupled. Mutations impairing MyD88-dependent toll-like receptor (TLR) signaling decreased the number of IAHC cells and LMPs but increased the number of HSCs in the aorta-gonad-mesonephros region of mouse embryos. TLR4 -deficient embryos generated normal numbers of HE cells but the proliferation of IAHC cells was decreased. Loss of MyD88-dependent TLR signaling in innate immune myeloid cells had no effect on IAHC cell numbers. Instead, TLR4 deletion in endothelial cells recapitulated the phenotype observed with germline deletion, demonstrating that MyD88-dependent TLR signaling in endothelial cells and/or in IAHCs regulates the balance between generating LMPs and HSCs. Summary StatementToll-like receptor signaling in endothelial cells restricts the number of hematopoietic stem cells but increases the number of committed progenitors and intra-arterial hematopoietic cluster cells by promoting their proliferation.

developmental biology↗

bioRxiv2020

In vivo CRISPR screening identifies Fli1 as a transcriptional safeguard that restrains effector CD8 T cell differentiation during infection and cancer

Improving effector activity of antigen specific T cells is a major goal in cancer immunotherapy. Despite the identification of several effector T cell (TEFF)-driving transcription factors (TF), the transcriptional coordination of TEFF biology remains poorly understood. We developed an in vivo T cell CRISPR screening platform and identified a novel mechanism restraining TEFF biology through the ETS family TF, Fli1. Genetic deletion of Fli1 enhanced TEFF responses without compromising memory or exhaustion precursors. Fli1 restrained TEFF lineage differentiation by binding to cis-regulatory elements of effector-associated genes. Loss of Fli1 increased chromatin accessibility at ETS:RUNX motifs allowing more efficient Runx3-driven TEFF biology. CD8 T cells lacking Fli1 provided substantially better protection against multiple infections and tumors. These data indicate that Fli1 safeguards the developing CD8 T cell transcriptional landscape from excessive ETS:RUNX-driven TEFF cell differentiation. Moreover, genetic deletion of Fli1 improves TEFF differentiation and protective immunity in infections and cancer.

immunology↗

bioRxiv2019

Transcriptional regulatory network controlling the ontogeny of hematopoietic stem cells

Hematopoietic stem cell (HSC) ontogeny is accompanied by dynamic changes in gene regulatory networks. We performed RNA-Seq and histone mark ChIP-Seq to define the transcriptomes and epigenomes of cells representing key developmental stages of HSC ontogeny in the mouse. The five populations analyzed were embryonic day 10.5 (E10.5) endothelium and hemogenic endothelium from the major arteries (dorsal aorta, umbilical and vitelline), an enriched population of pre-hematopoietic stem cells (pre-HSCs), fetal liver HSCs, and adult bone marrow HSCs. We observed dynamic and combinatorial epigenetic changes that mark regulatory DNA sequences including gene promoters and enhancers. Using epigenetic signatures, we identified enhancers for each developmental stage. Only 12% of enhancers are primed, and 78% are active, suggesting the vast majority of enhancers are established de novo at the developmental stages where they are required to control their target genes, without prior priming in earlier stages. We constructed developmental-stage-specific transcriptional regulatory networks during HSC ontogeny by linking enhancers and predicted bound transcription factors to their target promoters using a novel computational algorithm. Our computational analyses predicted known transcriptional regulators for the endothelial-to-hematopoietic transition, validating our overall approach, and identified putative novel transcription factors whose regulon activities correlate with the emergence of pre-HSCs. We validated roles for the broadly expressed transcription factors SP3 and MAZ in arterial hemogenic endothelium. Our data and computational analyses provide a useful resource for uncovering regulators of HSC formation.

developmental biology↗