Project description:During the step-wise specification and differentiation of tissue specific multipotent progenitor cells, lineage-specific transcriptional networks are either activated or repressed to orchestrate progenitor cell commitment. The gas exchange niche in the lung contains two major epithelial cell types, alveolar type 1 (AT1) and type 2 (AT2) cells, and the timing of lineage commitment of these cells is critical for correct formation of this niche and postnatal survival. To define the ontogeny of alveolar cell fate in the lung, we used lineage tracing studies combined with spatially specific mRNA transcript and protein expression combined with single cell RNA-seq analysis. These studies reveal that commitment to alveolar epithelial cell fate occurs far earlier than previously appreciated, concomitant with the proximal-distal specification of epithelial progenitors and branching morphogenesis. Using a novel dual lineage tracing system, we show that a small population of alveolar cells express markers of both AT1 and AT2 cells, whose fate is ultimately restricted to a single lineage. However, these bi-transcriptional cells generate only a minor portion of the mature alveolar epithelium. These data reveal a new paradigm of organ formation where early lineage commitment occurs during the nascent stages of development coincident with broad tissue patterning processes including axial patterning of the endoderm and branching morphogenesis.
Project description:Alveolar epithelial cell fate decisions drive lung development and regeneration. Using transcriptomic and epigenetic profiling coupled with genetic mouse and organoid models, we identified Klf5 as a critical regulator of alveolar epithelial cell fate across the lifespan. During prenatal lung development and alveologenesis, Klf5 enforces alveolar epithelial type 1 (AT1) cell lineage fidelity. While it is dispensable for both adult AT1 and alveolar epithelial type 2 (AT2) cell homeostasis, Klf5 regulates AT2 cell plasticity after injury. Klf5 represses AT2 cell proliferation and enhances AT2-AT1 cell differentiation in a spatially restricted manner in both infectious and non-infectious models of acute respiratory distress syndrome. Moreover, ex vivo organoid assays reveal that Klf5 modulates AT2 cell fate decisions through reducing AT2 cell sensitivity to inflammatory signaling. These data highlight a major transcriptional regulator of AT1 cell lineage commitment and of the AT2 cell response to inflammatory crosstalk during lung regeneration.
Project description:During the stepwise specification and differentiation of tissue-specific multipotent progenitors, lineage-specific transcriptional networks are activated or repressed to orchestrate cell specification. The gas-exchange niche in the lung contains two major epithelial cell types, alveolar type 1 (AT1) and AT2 cells, and the timing of lineage specification of these cells is critical for the correct formation of this niche and postnatal survival. Integrating cell-specific lineage tracing studies, spatially specific mRNA transcript and protein expression, and single-cell RNA-sequencing analysis, we demonstrate that specification of alveolar epithelial cell fate begins concomitantly with the proximal-distal specification of epithelial progenitors and branching morphogenesis earlier than previously appreciated. By using a newly developed dual-lineage tracing system, we show that bipotent alveolar cells that give rise to AT1 and AT2 cells are a minor contributor to the alveolar epithelial population. Furthermore, single-cell assessment of the transcriptome identifies specified AT1 and AT2 progenitors rather than bipotent cells during sacculation. These data reveal a paradigm of organ formation whereby lineage specification occurs during the nascent stages of development coincident with broad tissue-patterning processes, including axial patterning of the endoderm and branching morphogenesis.
Project description:Multipotent Nkx2-1-positive lung epithelial primordial progenitors of the foregut endoderm are thought to be the developmental precursors to all adult lung epithelial lineages. However, little is known about the global transcriptomic programs or gene networks that regulate these gateway progenitors in vivo due to their rarity and transient presence during a narrow developmental window, embryonic day E9.0 in mice. Here we describe the unique genetic program of in vivo lung primordial progenitors and computationally identify the signaling pathways that are involved in their cell-fate determination from pre-specified embryonic foregut. We integrate this information in computational models to generate in vitro engineered lung primordial progenitors from mouse pluripotent stem cells, improving the fidelity of the resulting cells through unbiased, easy-to-interpret similarity scores and modulation of cell culture conditions, including biomechanical cues. As the genetic characterization of early in vivo embryonic progenitors is rapidly expanding, the methodology proposed here can have wide applicability to the in vitro derivation of bona fide tissue progenitors of all germ layers.
Project description:Khajuria RK, Munschauer M, Ulirsch JC, Fiorini C, Leif S. Ludwig LS, McFarland SK, Abdulhay NJ, Specht H, Keshishian H, Mani DR, Jovanovic M, Ellis SR, Fulco CP, Engreitz JM, Schütz S, Lian J, Gripp KW,Weinberg OK, Pinkus GS, Gehrke L, Regev A, Lander ES, Gazda HT, Lee WY, Panse VG, Carr SA, Sankaran VG. Cell 2018, 173, 90–103. https://doi.org/10.1016/j.cell.2018.02.036.
Blood cell formation is classically thought to occur through a hierarchical differentiation process, although recent studies have shown that lineage commitment may occur earlier in hematopoietic stem and progenitor cells (HSPCs). The relevance to human blood diseases and the underlying regulation of these refined models remain poorly understood. By studying a genetic blood disorder, Diamond-Blackfan anemia (DBA), where the majority of mutations affect ribosomal proteins and the erythroid lineage is selectively perturbed, we are able to gain mechanistic insight into how lineage commitment is programmed normally and disrupted in disease. We show that in DBA, the pool of available ribosomes is limited, while ribosome composition remains constant. Surprisingly, this global reduction in ribosome levels more profoundly alters translation of a select subset of transcripts. We show how the reduced translation of select transcripts in HSPCs can impair erythroid lineage commitment, illuminating a regulatory role for ribosome levels in cellular differentiation.
Project description:B lymphopoiesis is a key developmental event orchestrated by a complex combinatorial action of lineage-specific transcription factors. In early B cell progenitors, lineage commitment is directly mediated by the master regulator PAX5, whose deficiency is commonly associated with B cell Acute Lymphoblastic Leukemia (B-ALL). Despite its essential role in mammalian immunity, the regulatory mechanisms that control PAX5 function remain largely unknown. Here we show that NAD+-dependent enzyme SIRT7 coordinates B cell development progression through PAX5. We have identified a SIRT7-dependent regulatory switch based on dynamic deacetylation of a single PAX5 residue, which controls its activity and thereby B cell fate. While a PAX5K198 acetylated mimic is incapable of inducing both B cell development and identity due to reduced protein stability and impaired binding to chromatin, deacetylation of this residue boosts PAX5 activity, leading to massive gene repression and in vivo restoration of B cell commitment but not differentiation. These findings suggest an unexpected uncoupling of hematopoietic differentiation and lineage commitment. Further supporting the functional relevance of the SIRT7-PAX5 axis, the interplay between both factors is conserved in human B-ALL, where high SIRT7 expression is an independent good prognostic factor. Our findings unveil a crucial mechanism in the regulation of B cell production based on the control of PAX5 function and underscore the key role of Sirtuins in the regulation of the immune system.