Summary Induced pluripotent stem cells (iPSCs) are commonly generated by transduction of Oct4, Sox2, Klf4, and Myc (OSKM) into cells. Although iPSCs are pluripotent, they frequently exhibit high variation in terms of quality, as measured in mice by chimera contribution and tetraploid complementation. Reliably high-quality iPSCs will be needed for future therapeutic applications. Here, we show that one major determinant of iPSC quality is the combination of reprogramming factors used. Based on tetraploid complementation, we found that ectopic expression of Sall4, Nanog, Esrrb, and Lin28 (SNEL) in mouse embryonic fibroblasts (MEFs) generated high-quality iPSCs more efficiently than other combinations of factors including OSKM. Although differentially methylated regions, transcript number of master regulators, establishment of specific superenhancers, and global aneuploidy were comparable between high- and low-quality lines, aberrant gene expression, trisomy of chromosome 8, and abnormal H2A.X deposition were distinguishing features that could potentially also be applicable to human.

Brown adipose tissue (BAT) is responsible for thermogenesis that is not associated with shivering through the process of converting chemical energy into heat through uncoupling protein 1 (UCP1) in the mitochondria. Thus, expanding or activating BAT could be a potential tool against obesity. To analyze the effect of kinase signaling on brown adipocyte formation, a process that describes the acquisition of the ability to dissipate energy as heat, we performed lentiviral-mediated short hairpin knockdown or used pharmacological inhibitors in a high-content and high-throughput in vitro image-based screen. We identified 190 kinases that either stimulated or inhibited brown adipocyte proliferation, differentiation, or formation. Among these kinases, we found that 5' AMP-activated protein kinase (AMPK) promoted the formation of brown adipocytes abundant inUCP1. Together, our results provide insight into the kinases, particularly AMPK, that regulate brown adipocyte formation.

Highlights d Generation of a mouse model to ablate UCP1 + cells in mice using diphtheria toxin d Deletion of UCP1 + cells does not change energy expenditure at room temperature d UCP1 + cells do not contribute to circulating FGF21 levels after cold exposure d FGF21-dependent increase in EE and glucose tolerance is dependent on UCP1 + cells

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