A genetic disorder reveals a hematopoietic stem cell regulatory network co-opted in leukemia

The molecular regulation of human hematopoietic stem cell (HSC) self-renewal is therapeutically important, but limitations in experimental systems and interspecies variation have constrained our knowledge of this process. Here, we have studied a rare genetic disorder due to MECOM haploinsufficiency, characterized by an early-onset absence of HSCs in vivo. By generating a faithful model of this disorder in primary human HSCs and coupling functional studies with integrative single-cell genomic analyses, we uncover a key transcriptional network involving hundreds of genes that is required for HSC self-renewal. Through our analyses, we nominate cooperating transcriptional regulators and identify how MECOM prevents the CTCF-dependent genome reorganization that occurs as HSCs exit quiescence. Strikingly, we show that this transcriptional network is co-opted in high-risk leukemias, thereby enabling these cancers to acquire stem cell properties. Collectively, we illuminate a regulatory network necessary for HSC self-renewal through the study of a rare experiment of nature.

Whole transcriptome-sequencing and network analysis of CD1c+ human dendritic cells identifies cytokine-secreting subsets linked to type I IFN-negative autoimmunity to the eye

Background: Inflammatory subsets of CD1c+ conventional dendritic cells (CD1c+ DCs) are promoted by type I interferons (IFN), but the molecular basis for CD1c+ DCs involvement in conditions not driven by type I IFNs is unknown. Methods: Our objective was to use RNA-sequencing of blood CD1c+ DCs and high-dimensional flow cytometry of two cohorts of autoimmune uveitis patients and healthy donors to characterize the CD1c+ DCs population of type I IFN-negative autoimmune uveitis. Results: We report that the CD1c+ DCs pool from patients with autoimmune uveitis (n=45) is skewed towards a transcriptional network characterized by surface receptor genes CX3CR1, CCR2, and CD36. We confirmed the association of the transcriptional network with autoimmune uveitis by RNA-sequencing in another case-control cohort (n=35) and demonstrated that this network was governed by NOTCH2-RUNX3 signaling. Unbiased flow cytometry analysis based on the transcriptional network identified blood CD1c+ DC subsets that can be distinguished by CX3CR1 and CD36 surface expression. A CD36+CX3CR1+CD1c+ DC subset within the novel DC3 population was diminished in peripheral blood of patients, while CD1c+ DCs expressing CD36 and CX3CR1 accumulate locally in the inflamed eye. The CD36+CX3CR1+CD1c+ DC subset showed a differential capacity to produce cytokines, including TNF-alpha, IL-6, and VEGF, but not IL-23. Conclusion: These results show that CD1c+ DC subsets defined on the basis of surface expression of CD36 and CX3CR1 are linked to type I IFN-negative human autoimmune uveitis and show a differential capacity to secrete proinflammatory mediators that drive its pathophysiology.

BBX16 mediates the repression of seedling photomorphogenesis downstream of the GUN1-GLK1 module during retrograde signaling

Plastid-to-nucleus retrograde signals (RS) initiated by dysfunctional chloroplasts impact photomorphogenic development. We previously showed that the transcription factor GLK1 acts downstream of the RS-regulator GUN1 in photodamaging conditions to regulate not only the well-established expression of photosynthesis-associated nuclear genes (PhANGs) but also to regulate seedling morphogenesis. Specifically, the GUN1/GLK1 module inhibits the light-induced PIF-repressed transcriptional network to suppress cotyledon development when chloroplast integrity is compromised, modulating the area exposed to potentially damaging high light. However, how the GUN1/GLK1 module inhibits photomorphogenesis upon chloroplast damage remained undefined. Here, we report the identification of BBX16 as a novel direct target of GLK1. BBX16 is induced and promotes photomorphogenesis in moderate light and it is repressed via GUN1/GLK1 after chloroplast damage. Additionally, we show that BBX16 represents a regulatory branching point downstream of GUN1/GLK1 in the regulation of PhANG expression and seedling development upon RS activation. The gun1 phenotype in lincomycin and the gun1-like phenotype of GLK1OX are markedly suppressed in gun1bbx16 and GLK1OXbbx16. This study identifies BBX16 as the first member of the BBX family involved in RS, and defines a molecular bifurcation mechanism operated by GLK1/BBX16 to optimize seedling deetiolation, and to ensure photoprotection in unfavorable light conditions.

Multi-omic approach identifies a transcriptional network coupling innate immune response to proliferation in the blood of COVID-19 cancer patients

Clinical outcomes of COVID-19 patients are worsened by the presence of co-morbidities, especially cancer leading to elevated mortality rates. SARS-CoV-2 infection is known to alter immune system homeostasis. Whether cancer patients developing COVID-19 present alterations of immune functions which might contribute to worse outcomes have so far been poorly investigated. We conducted a multi-omic analysis of immunological parameters in peripheral blood mononuclear cells (PBMCs) of COVID-19 patients with and without cancer. Healthy donors and SARS-CoV-2-negative cancer patients were also included as controls. At the infection peak, cytokine multiplex analysis of blood samples, cytometry by time of flight (CyTOF) cell population analyses, and Nanostring gene expression using Pancancer array on PBMCs were performed. We found that eight pro-inflammatory factors (IL-6, IL-8, IL-13, IL-1ra, MIP-1a, IP-10) out of 27 analyzed serum cytokines were modulated in COVID-19 patients irrespective of cancer status. Diverse subpopulations of T lymphocytes such as CD8+T, CD4+T central memory, Mucosal-associated invariant T (MAIT), natural killer (NK), and γδ T cells were reduced, while B plasmablasts were expanded in COVID-19 cancer patients. Our findings illustrate a repertoire of aberrant alterations of gene expression in circulating immune cells of COVID-19 cancer patients. A 19-gene expression signature of PBMCs is able to discriminate COVID-19 patients with and without solid cancers. Gene set enrichment analysis highlights an increased gene expression linked to Interferon α, γ, α/β response and signaling which paired with aberrant cell cycle regulation in cancer patients. Ten out of the 19 genes, validated in a real-world consecutive cohort, were specific of COVID-19 cancer patients independently from different cancer types and stages of the diseases, and useful to stratify patients in a COVID-19 disease severity-manner. We also unveil a transcriptional network involving gene regulators of both inflammation response and proliferation in PBMCs of COVID-19 cancer patients.

Excessive fetal growth affects HSC quiescence maintenance through epigenetic programming of EGR1 transcriptional network

Fetal development is a critical period to shape stem cell identity and functions. Detrimental environments during this period are associated with epigenetics alteration of hematopoietic stem and progenitor cells (HSPC) with unknown functional impacts. We implemented a single-cell resolution integrative analysis combining epigenomics, transcriptomics, and functional data to elucidate the epigenetic influence associated with excessive fetal growth on HSPCs. We showed that hematopoietic stem cells (HSC) from large for gestational age neonates present a coordinated DNA hypermethylation and decrease expression for genes of the EGR1 transcriptional network including SOCS3, KLF2, and JUNB known to sustain stem cell quiescence and pluripotency. Furthermore, these changes were associated with a decreased ability for HSCs to stay undifferentiated and a decreased ability to expand in response to stimulation. Taken together, these results show that fetal overgrowth affects hematopoietic stem cells quiescence maintenance program through an epigenetic programming of the EGR1 related transcriptional network.

A hierarchical transcriptional network activates specific CDK inhibitors that regulate G2 to control cell size and number in Arabidopsis

How cell size and number are determined during organ development remains a fundamental question in cell biology. Here, we identified a GRAS family transcription factor, called SCARECROW-LIKE28 (SCL28), with a critical role in determining cell size in Arabidopsis. SCL28 is part of a transcriptional regulatory network downstream of the central MYB3Rs that regulate G2 to M phase cell cycle transition. We show that SCL28 forms a dimer with the AP2-type transcription factor, AtSMOS1, which defines the specificity for promoter binding and directly activates transcription of a specific set of SIAMESE-RELATED (SMR) family genes, encoding plant-specific inhibitors of cyclin-dependent kinases and thus inhibiting cell cycle progression at G2 and promoting the onset of endoreplication. Through this dose-dependent regulation of SMR transcription, SCL28 quantitatively sets the balance between cell size and number without dramatically changing final organ size. We propose that this hierarchical transcriptional network constitutes a cell cycle regulatory mechanism that allows to adjust cell size and number to attain robust organ growth.