Differentiation of functional thyroid epithelia from pluripotent stem cells (PSCs) holds the potential for application in regenerative medicine. However, progress toward this goal is hampered by incomplete understanding of the signaling pathways needed for directed differentiation without forced over-expression of exogenous transgenes. Here we use mouse PSCs to identify key conserved roles for BMP and FGF signaling in regulating thyroid lineage specification from foregut endoderm in mouse and Xenopus. Thyroid progenitors derived from mouse PSCs can be matured into thyroid follicular organoids that provide functional secretion of thyroid hormones in vivo and rescue hypothyroid mice after transplantation. Moreover, by stimulating the same pathways we were also able to derive human thyroid progenitors from normal and disease-specific iPSCs generated from patients with hypothyroidism resulting from NKX2-1 haploinsufficiency. Our studies have therefore uncovered the regulatory mechanisms that underlie early thyroid organogenesis and provide a significant step toward cell-based regenerative therapy for hypothyroidism.

SummaryEfficient differentiation of pluripotent cells to proximal and distal lung epithelial cell populations remains a challenging task. The 3D extracellular matrix (ECM) scaffold is a key component that regulates the interaction of secreted factors with cells during development by often binding to and limiting their diffusion within local gradients. Here we examined the role of the lung ECM in differentiation of pluripotent cells in vitro and demonstrate the robust inductive capacity of the native lung matrix alone. Extended culture of stem cell-derived definitive endoderm on decellularized lung scaffolds in defined, serum-free medium resulted in differentiation into mature airway epithelia, complete with ciliated cells, club cells, and basal cells with morphological and functional similarities to native airways. Heparitinase I, but not chondroitinase ABC, treatment of scaffolds revealed that the differentiation achieved is dependent on heparan sulfate proteoglycans and its bound factors remaining on decellularized scaffolds.

SummaryLung development-associated diseases are major causes of morbidity and lethality in preterm infants and children. Access to the lung progenitor/stem cell populations controlling pulmonary development during embryogenesis and early postnatal years is essential to understand the molecular basis of such diseases. Using a Nkx2-1mCherry reporter mouse, we have identified and captured Nkx2-1-expressing lung progenitor cells from the proximal lung epithelium during fetal development. These cells formed clonal spheres in semisolid culture that could be maintained in vitro and demonstrated self-renewal and expansion capabilities over multiple passages. In-vitro-derived Nkx2-1-expressing clonal spheres differentiated into a polarized epithelium comprised of multiple cell lineages, including basal and secretory cells, that could repopulate decellularized lung scaffolds. Nkx2-1 expression thus defines a fetal lung epithelial progenitor cell population that can be used as a model system to study pulmonary development and associated pediatric diseases.

Key PointsEngineered human models of high-fatality pediatric leukemia are relevant to uncover disease biomarkers and therapeutic vulnerabilities. NUP98-KDM5A–associated AMKL expresses SELP, MPIG6B, and NEO1 biomarkers and is sensitive to pharmacologic inhibition with ruxolitinib.

In a functional genomics screen of mouse embryonic stem cells (ESCs) with nested hemizygous chromosomal deletions, we reveal that ribosomal protein (RP) genes are the most significant haploinsufficient determinants for embryoid body (EB) formation. Hemizygocity for three RP genes (Rps5, Rps14, or Rps28), distinguished by the proximity of their corresponding protein to the ribosome's mRNA exit site, is associated with the most profound phenotype. This EB phenotype was fully rescued by BAC or cDNA complementation but not by the reduction of p53 levels, although such reduction was effective with most other RP-deleted clones corresponding to non-mRNA exit-site proteins. RNAsequencing studies further revealed that undifferentiated ESCs hemizygous for Rps5 showed reduced expression levels of several mesoderm-specific genes as compared with wild-type counterparts. Together, these results reveal that RP gene dosage limits the differentiation, not the self-renewal, of mouse ESCs. They also highlight two separate mechanisms underlying this process, one of which is p53 independent.embryonic stem cells | differentiation | embryoid body | ribosomal proteins E mbryonic stem cell (ESC) fate is intricately controlled at the transcriptional level by factors such as Oct4 (Pou5f1), Sox2 and Nanog (1-3), Dax1, Rex1, and SalI (reviewed in ref. 4), and the Mediator complex (3, 5, 6). Although much progress has been made on the identification of the transcriptional circuitry that defines pluripotency, the regulation of mRNA translation and posttranslational protein modifications currently are considered in this context only as fine-tuning to balance protein production and activity (7).ESC self-renewal can be assessed readily by their ability to give rise to undifferentiated progeny in a clonal fashion. Similarly, in the absence of leukemia inhibitory factor (LIF) and bone morphogenetic protein signaling, ESC pluripotent potential can be investigated in vitro by initiating differentiation of the three germ layers using an embryoid body (EB) formation assay (8, 9).To identify novel regulators of ESC fate, we developed a retrovirus-based methodology that randomly generates hemizygous chromosomal deletions with increasing size (nested) (Fig. 1A and detailed in ref. 10). Using this method, we reported the generation of a library of 1,307 ESC clones covering more than 25% of the mouse genome (the DelES library) along with an improved methodology for BAC recombineering and complementation (11). Phenotypical characteristics and a genetic map of all clones in our DelES collection are available at www.bioinfo.iric.ca/deles.Here, we report the integrative analysis linking the physical mapping to phenotype for all 1,307 clones in our library, documenting that genes involved in ribosome biogenesis and function are key players in ESC fate. We tested this hypothesis extensively in functional studies and identified a p53-independent response to ribosomal stress for mRNA exit-site ribosomal proteins (RPs). ResultsGene Ontology Term Analysis Identifies...