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An essential aspect of stem cell culture is the successful maintenance of the undifferentiated state. Many types of stem cells are FGF2 dependent,and pluripotent stem cells are maintained by replacing FGF2-containing media daily,while tissue-specific stem cells are typically fed every 3rd day. Frequent feeding,however,results in significant variation in growth factor levels due to FGF2 instability,which limits effective maintenance due to spontaneous differentiation. We report that stabilization of FGF2 levels using controlled release PLGA microspheres improves expression of stem cell markers,increases stem cell numbers and decreases spontaneous differentiation. The controlled release FGF2 additive reduces the frequency of media changes needed to maintain stem cell cultures,so that human embryonic stem cells and induced pluripotent stem cells can be maintained successfully with biweekly feedings. View Publication

The mammalian central nervous system (CNS) undergoes significant expansion postnatally,producing astrocytes,oligodendrocytes and inhibitory neurons to modulate the activity of neural circuits. This is coincident in humans with the emergence of pediatric epilepsy,a condition commonly treated with valproate/valproic acid (VPA),a potent inhibitor of histone deacetylases (HDACs). The sequential activity of specific HDACs,however,may be essential for the differentiation of distinct subpopulations of neurons and glia. Here,we show that different subsets of CNS neural stem cells (NSCs) and progenitors switch expression of HDAC1 and HDAC2 as they commit to a neurogenic lineage in the subventricular zone (SVZ) and dentate gyrus (DG). The administration of VPA for only one week from P7-P14,combined with sequential injections of thymidine analogs reveals that VPA stimulates a significant and differential decrease in the production and differentiation of progeny of NSCs in the DG,rostral migratory stream (RMS),and olfactory bulb (OB). Cross-fostering VPA-treated mice revealed,however,that a postnatal failure to thrive induced by VPA treatment had a greater effect on DG neurogenesis than VPA action directly. By one month after VPA,OB interneuron genesis was significantly and differentially reduced in both periglomerular and granule neurons. Using neurosphere assays to test if VPA directly regulates NSC activity,we found that short term treatment with VPA in vivo reduced neurosphere numbers and size,a phenotype that was also obtained in neurospheres from control mice treated with VPA and an alternative HDAC inhibitor,Trichostatin A (TSA) at 0 and 3 days in vitro (DIV). Collectively,these data show that clinically used HDAC inhibitors like VPA and TSA can perturb postnatal neurogenesis; and their use should be carefully considered,especially in individuals whose brains are actively undergoing key postnatal time windows of development. View Publication

Identification and quantification of the characteristics of stem cell preparations is critical for understanding stem cell biology and for the development and manufacturing of stem cell based therapies. We have developed image analysis and visualization software that allows effective use of time-lapse microscopy to provide spatial and dynamic information from large numbers of human embryonic stem cell colonies. To achieve statistically relevant sampling,we examined textgreater 680 colonies from 3 different preparations of cells over 5 days each,generating a total experimental dataset of 0.9 terabyte (TB). The 0.5 Giga-pixel images at each time point were represented by multi-resolution pyramids and visualized using the Deep Zoom Javascript library extended to support viewing Giga-pixel images over time and extracting data on individual colonies. We present a methodology that enables quantification of variations in nominally-identical preparations and between colonies,correlation of colony characteristics with Oct4 expression,and identification of rare events. View Publication

Human coronaviruses (HCoVs) enter cells via two distinct pathways: the endosomal pathway using cathepsins to activate spike protein and the cell-surface or early endosome pathway using extracellular proteases such as transmembrane protease serine 2 (TMPRSS2). We previously reported that clinical isolates of HCoV-229E preferred cell-surface TMPRSS2 to endosomal cathepsin for cell entry,and that they acquired the ability to use cathepsin L by repeated passage in cultured cells and were then able to enter cells via the endosomal pathway. Here,we show that clinical isolates of HCoV-OC43 and -HKU1 preferred the cell-surface TMRRSS2 to endosomal cathepsins for cell entry,similar to HCoV-229E. In addition,the cell-culture-adapted HCoV-OC43 lost the ability to infect and replicate in air-liquid interface cultures of human bronchial tracheal epithelial cells. These results suggest that circulating HCoVs in the field generally use cell-surface TMPRSS2 for cell entry,not endosomal cathepsins,in human airway epithelial cells. View Publication

Type I Interferons (IFN-I) are central to host protection against viral infections,with plasmacytoid dendritic cells (pDC) being the most significant source,yet pDCs lose their IFN-I production capacity following an initial burst of IFN-I,resulting in susceptibility to secondary infections. The underlying mechanisms of these dynamics are not well understood. Here we find that viral infection reduces the capacity of pDCs to engage both oxidative and glycolytic metabolism. Mechanistically,we identify lactate dehydrogenase B (LDHB) as a positive regulator of pDC IFN-I production in mice and humans; meanwhile,LDHB deficiency is associated with suppressed IFN-I production,pDC metabolic capacity,and viral control following infection. In addition,preservation of LDHB expression is sufficient to partially retain the function of otherwise exhausted pDCs,both in vitro and in vivo. Furthermore,restoring LDHB in vivo in pDCs from infected mice increases IFNAR-dependent,infection-associated pathology. Our work thus identifies a mechanism for balancing immunity and pathology during viral infections,while also providing insight into the highly preserved infection-driven pDC inhibition. Plasmacytoid dendritic cells (pDC) are the major IFN-I-producing cells,but this production returns to baseline soon after viral infection. Here the authors show that this decrease in IFN-I production and related pDC functions may be attributed to suppressed oxidative and glycolytic metabolism of pDCs,with lactate dehydrogenase B identified as a regulator. View Publication

Acute myeloid leukemia (AML) is primarily driven by leukemic stem cells (LSCs),the main cause of relapse and therapy resistance. Here,we discover that LSCs are predominantly small and mechanically soft. These mechanical properties enable their selective isolation using microfluidic chips. Single-cell RNA-sequencing of primary human AML bone marrow identifies enrichment of LSCs within the FSClow ALDH1A1+ subpopulation,which exhibits long-term stemness in functional assays. Notably,inhibiting ALDH1A1 in these cells promotes F-actin polymerization and increases cellular stiffness,reducing their stemness while enhancing their susceptibility to natural killer (NK) cell-mediated cytotoxicity. In AML patient-derived xenograft models,the combination of ALDH1A1 inhibition with NK cell therapy markedly suppresses leukemia progression. These findings suggest that targeting the mechanical properties of LSC offers a promising strategy to overcome AML treatment resistance,providing insights into stem cell mechanobiology and paving the way for combining targeted therapies with immunotherapy to improve clinical outcomes. Leukemic stem cells (LSCs) drive relapse and therapy resistance in acute myeloid leukemia (AML). Here,the authors show that increasing the stiffness of LSCs reduces their stemness and enhances their susceptibility to natural killer cell-mediated immunotherapy in AML. View Publication

The differentiation of human pluripotent stem cells toward the hepatocyte lineage can potentially provide an unlimited source of functional hepatocytes for transplantation and extracorporeal bioartificial liver applications. It is anticipated that the quantities of cells needed for these applications will be in the order of 10(9)-10(10) cells,because of the size of the liver. An ideal differentiation protocol would be to enable directed differentiation to the hepatocyte lineage with simultaneous cell expansion. We introduced a cell expansion stage after the commitment of human embryonic stem cells to the endodermal lineage,to allow for at least an eightfold increase in cell number,with continuation of cell maturation toward the hepatocyte lineage. The progressive changes in the transcriptome were measured by expression array,and the expression dynamics of certain lineage markers was measured by mass cytometry during the differentiation and expansion process. The findings revealed that while cells were expanding they were also capable of progressing in their differentiation toward the hepatocyte lineage. In addition,our transcriptome,protein and functional studies,including albumin secretion,drug-induced CYP450 expression and urea production,all indicated that the hepatocyte-like cells obtained with or without cell expansion are very similar. This method of simultaneous cell expansion and hepatocyte differentiation should facilitate obtaining large quantities of cells for liver cell applications. View Publication

The airways are lined by secretory and multiciliated cells which function together to remove particles and debris from the respiratory tract. The transcriptome of multiciliated cells has been extensively studied,but the function of many of the genes identified is unknown. We have established an assay to test the ability of over-expressed transcripts to promote multiciliated cell differentiation in mouse embryonic tracheal explants. Overexpression data indicated that Fibronectin type 3 and ankyrin repeat domains 1 (Fank1) and JAZF zinc finger 1 (Jazf1) promoted multiciliated cell differentiation alone,and cooperatively with the canonical multiciliated cell transcription factor Foxj1. Moreover,knock-down of Fank1 or Jazf1 in adult mouse airway epithelial cultures demonstrated that these factors are both required for ciliated cell differentiation in vitro This analysis identifies Fank1 and Jazf1 as novel regulators of multiciliated cell differentiation. Moreover,we show that they are likely to function downstream of IL6 signalling and upstream of Foxj1 activity in the process of ciliated cell differentiation. In addition,our in vitro explant assay provides a convenient method for preliminary investigation of over-expression phenotypes in the developing mouse airways.This article has an associated First Person interview with the first author of the paper. View Publication

Retinal ganglion cells (RGCs) are the projection neurons of the retina and transmit visual information to postsynaptic targets in the brain. While this function is shared among nearly all RGCs,this class of cell is remarkably diverse,comprised of multiple subtypes. Previous efforts have identified numerous RGC subtypes in animal models,but less attention has been paid to human RGCs. Thus,efforts of this study examined the diversity of RGCs differentiated from human pluripotent stem cells (hPSCs) and characterized defined subtypes through the expression of subtype-specific markers. Further investigation of these subtypes was achieved using single-cell transcriptomics,confirming the combinatorial expression of molecular markers associated with these subtypes,and also provided insight into more subtype-specific markers. Thus,the results of this study describe the derivation of RGC subtypes from hPSCs and will support the future exploration of phenotypic and functional diversity within human RGCs. View Publication

The study of induced pluripotency is complicated by the need for infection with high-titer retroviral vectors,which results in genetically heterogeneous cell populations. We generated genetically homogeneous 'secondary' somatic cells that carry the reprogramming factors as defined doxycycline (dox)-inducible transgenes. These cells were produced by infecting fibroblasts with dox-inducible lentiviruses,reprogramming by dox addition,selecting induced pluripotent stem cells and producing chimeric mice. Cells derived from these chimeras reprogram upon dox exposure without the need for viral infection with efficiencies 25- to 50-fold greater than those observed using direct infection and drug selection for pluripotency marker reactivation. We demonstrate that (i) various induction levels of the reprogramming factors can induce pluripotency,(ii) the duration of transgene activity directly correlates with reprogramming efficiency,(iii) cells from many somatic tissues can be reprogrammed and (iv) different cell types require different induction levels. This system facilitates the characterization of reprogramming and provides a tool for genetic or chemical screens to enhance reprogramming. View Publication

Wnt signalling is involved in numerous events in animal development,including the proliferation of stem cells and the specification of the neural crest. Wnt proteins are potentially important reagents in expanding specific cell types,but in contrast to other developmental signalling molecules such as hedgehog proteins and the bone morphogenetic proteins,Wnt proteins have never been isolated in an active form. Although Wnt proteins are secreted from cells,secretion is usually inefficient and previous attempts to characterize Wnt proteins have been hampered by their high degree of insolubility. Here we have isolated active Wnt molecules,including the product of the mouse Wnt3a gene. By mass spectrometry,we found the proteins to be palmitoylated on a conserved cysteine. Enzymatic removal of the palmitate or site-directed and natural mutations of the modified cysteine result in loss of activity,and indicate that the lipid is important for signalling. The purified Wnt3a protein induces self-renewal of haematopoietic stem cells,signifying its potential use in tissue engineering. View Publication

Recent studies have shown that NK-dendritic cell (DC) interaction plays an important role in the induction of immune response against tumors and certain viruses. Although the effect of this interaction is bidirectional,the mechanism or molecules involved in this cross-talk have not been identified. In this study,we report that coculture with NK cells causes several fold increase in IL-12 production by Toxoplasma gondii lysate Ag-pulsed DC. This interaction also leads to stronger priming of Ag-specific CD8+ T cell response by these cells. In vitro blockade of NKG2D,a molecule present on human and murine NK cells,neutralizes the NK cell-induced up-regulation of DC response. Moreover,treatment of infected animals with Ab to NKG2D receptor compromises the development of Ag-specific CD8+ T cell immunity and reduces their ability to clear parasites. These studies emphasize the critical role played by NKG2D in the NK-DC interaction,which apparently is important for the generation of robust CD8+ T cell immunity against intracellular pathogens. To the best of our knowledge,this is the first work that describes in vivo importance of NKG2D during natural infection. View Publication