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Key Points KAT2A is required at different stages of human cord blood erythroid development with ATAC and SAGA complex specificity.KAT2A regulates leukemia cell maintenance and identity through specific participation in ATAC and SAGA complexes., Visual Abstract, Epigenetic histone modifiers are key regulators of cell fate decisions in normal and malignant hematopoiesis. Their enzymatic activities are of particular significance as putative therapeutic targets in leukemia. In contrast, less is known about the contextual role in which those enzymatic activities are exercised and specifically how different macromolecular complexes configure the same enzymatic activity with distinct molecular and cellular consequences. We focus on KAT2A, a lysine acetyltransferase responsible for histone H3 lysine 9 acetylation, which we recently identified as a dependence in acute myeloid leukemia stem cells and that participates in 2 distinct macromolecular complexes: Ada two-A-containing (ATAC) and Spt-Ada-Gcn5-Acetyltransferase (SAGA). Through analysis of human cord blood hematopoietic stem cells and progenitors, and of myeloid leukemia cells, we identify unique respective contributions of the ATAC complex to regulation of biosynthetic activity in undifferentiated self-renewing cells and of the SAGA complex to stabilization or correct progression of cell type–specific programs with putative preservation of cell identity. Cell type and stage-specific dependencies on ATAC and SAGA-regulated programs explain multilevel KAT2A requirements in leukemia and in erythroid lineage specification and development. Importantly, they set a paradigm against which lineage specification and identity can be explored across developmental stem cell systems.

International audience; Group 3 innate lymphoid cells (ILC3) have been detected in both murine and human decidual tissues where they are thought to play a relevant role in the induction and maintenance of pregnancy. However, limited information exists on the molecular mechanisms that regulate these cells, including immune checkpoints. Here, we show that ILC3 express the inhibitory checkpoints programmed cell death (PD-1) and T cell immunoglobulin and mucin domain containing protein 3 (TIM-3) during the first trimester of pregnancy and that these receptors could regulate production of cytokines, including IL-22, IL-8, and TNF-α, induced by IL-23. We also show that the intermediate extravillous trophoblast (iEVT) expresses high levels of the PD-1-ligand PD-L1, suggesting that PD-1/PD-L1 interaction may regulate ILC3 function at the feto-maternal interface. Our present data provide the first evidence that human decidual ILC3 express a functional PD-1. It is possible that an altered expression or function of PD-1 may break the immune-tolerance resulting in pregnancy failure.

Due to their osteoconductive and inductive properties, a variety of calcium phosphate (CaP) scaffolds are commonly used in orthopaedics as graft material to heal bone defects. In this study, we have used two CaP scaffolds with different hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) ratios (MBCP®; 60/40 and MBCP+ ®; 20/80) to investigate their intrinsic capacity to favour human bone marrow stem cells (hBMSCs) osteogenic differentiation capacity. We report that MBCP+ ® showed in in vitro culture model a higher rate of calcium ion release in comparison with MBCP®. In two defined coculture systems, the hBMSC seeded onto MBCP+ ® presented an increased amount of VEGF secretion, resulting in an enhanced endothelial cell proliferation and capillary formation compared with hBMSC seeded onto MBCP®. When both ceramics combined with hBMSC were implanted in a nude mouse model, we observed a faster osteogenic differentiation and enhancement mature bone deposition sustained by the presence of a vast host vasculature within the MBCP+ ® ceramics. Bone formation was observed in samples highly positive to the activation of calcium sensing receptor protein (CaSr) on the surface of seeded hBMSC that also shown higher BMP-2 protein expression. With these data we provide valuable insights in the possible mechanisms of ossification and angiogenesis by hBMSC that we believe to be primed by calcium ions released from CaP scaffolds. Evidences could lead to an optimization of ceramic scaffolds to prime bone repair.

International audience; Mutations in TBC1D24 are described in patients with a spectrum of neurological diseases, including mild and severe epilepsies and complex syndromic phenotypes such as Deafness, Onycodystrophy, Osteodystrophy, Mental Retardation and Seizure (DOORS) syndrome. The product of TBC1D24 is a multifunctional protein involved in neuronal development, regulation of synaptic vesicle trafficking, and protection from oxidative stress. Although pathogenic mutations in TBC1D24 span the entire coding sequence, no clear genotype/phenotype correlations have emerged. However most patients bearing predicted loss of function mutations exhibit a severe neurodevelopmental disorder. Aim of the study is to investigate the impact of TBC1D24 knockdown during the first stages of neuronal differentiation when axonal specification and outgrowth take place. In rat cortical primary neurons silenced for TBC1D24, we found defects in axonal specification, the maturation of axonal initial segment and action potential firing. The axonal phenotype was accompanied by an impairment of endocytosis at the growth cone and an altered activation of the TBC1D24 molecular partner ADP ribosylation factor 6. Accordingly, acute knockdown of TBC1D24 in cerebrocortical neurons in vivo analogously impairs callosal projections. The axonal defect was also investigated in human induced pluripotent stem cell-derived neurons from patients carrying TBC1D24 mutations. Reprogrammed neurons from a patient with severe developmental encephalopathy show significant axon formation defect that were absent from reprogrammed neurons of a patient with mild early onset epilepsy. Our data reveal that alterations of membrane trafficking at the growth cone induced by TBC1D24 loss of function cause axonal and excitability defects. The axonal phenotype correlates with the disease severity and highlight an important role for TBC1D24 in connectivity during brain development.

International audience; Decidual and uterine natural killer (NK) cells have been shown to contribute to the successful pregnancy both in humans and mice. NK cells represent "cytotoxic" group 1 innate lymphoid cells (ILCs) and are distinct from the recently described "helper" ILC1. Here, we show that both in humans and mice the majority of group 1 ILC in endometrium/uterus and decidua express Eomesodermin (Eomes), thus suggesting that they are developmentally related to conventional NK cells. However, they differ from peripheral NK cells. In humans, Eomes(+) decidual NK (dNK) cells express CD49a and other markers of tissue residency, including CD103, integrin β7, CD9, and CD69. The expression of CD103 allows the identification of different subsets of IFNγ-producing Eomes(+) NK cells. We show that TGFβ can sustain/induce CD103 and CD9 expression in dNK cells and decidual CD34-derived NK cells, indicating that the decidual microenvironment can instruct the phenotype of Eomes(+) NK cells. In murine decidua and uterus, Eomes(+) cells include CD49a(-)CD49b(+) conventional NK cells and CD49a(+) cells. Notably, Eomes(+)CD49a(+) cells are absent in spleen and liver. Decidual and uterine Eomes(+)CD49a(+) cells can be dissected in two peculiar cell subsets according to CD49b expression. CD49a(+)CD49b ((-)) and CD49a(+)CD49b(+) cells are enriched in immature CD11b(low)CD27(high) cells, while CD49a(-)CD49b(+) cells contain higher percentages of mature CD11b(high)CD27(low) cells, both in uterus and decidua. Moreover, Eomes(+)CD49a(+)CD49b(-) cells decrease during gestation, thus suggesting that this peculiar subset may be required in early pregnancy rather than on later phases. Conversely, a minor Eomes(-)CD49a(+) ILC1 population present in decidua and uterus increases during pregnancy. CD49b(-)Eomes(\textpm) cells produce mainly TNF, while CD49a(-)CD49b(+) conventional NK cells and CD49a(+)CD49b(+) cells produce both IFNγ and TNF. Thus, human and murine decidua contains unique subsets of group 1 ILCs, including Eomes(+) and Eomes(-) cells, with peculiar phenotypic and functional features. Our study contributes to re-examination of the complexity of uterine and decidual ILC subsets in humans and mice and highlights the role of the decidual microenvironment in shaping the features of these cells.