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Stem cell fate is largely determined by cellular signaling networks and is heavily dependent on the supplementation of exogenous recombinant proteins into culture media; however, uneven distribution and inconsistent stability of recombinant proteins are closely associated with the spontaneous differentiation of pluripotent stem cells (PSCs) and result in significant costs in large-scale manufacturing. Here, we report a novel PSC culture system via wirelessly controllable optical activation of the fibroblast growth factor (FGF) signaling pathway without the need for supplementation of recombinant FGF2 protein, a key molecule for maintaining pluripotency of PSCs. Using a fusion protein between the cytoplasmic region of the FGF receptor-1 and a light-oxygen-voltage domain, we achieved tunable, blue light-dependent activation of FGF signaling in human and porcine PSCs. Our data demonstrate that a highly controllable optical stimulation of the FGF signaling pathway is sufficient for long-term maintenance of PSCs, without the loss of differentiation potential into three germ layers. This culture system will be a cost-effective platform for a large-scale stem cell culture.

Histone-modifying enzymes play a pivotal role in gene expression and repression. In human, DOT1L (Dot1-like) is the only known histone H3 lysine 79 methyltransferase. hDOT1L is associated with transcriptional activation, but the general mechanism connecting hDOT1L to active transcription remains largely unknown. Here, we report that hDOT1L interacts with the phosphorylated C-terminal domain of actively transcribing RNA polymerase II (RNAPII) through a region conserved uniquely in multicellular DOT1 proteins. Genome-wide profiling analyses indicate that the occupancy of hDOT1L largely overlaps with that of RNAPII at actively transcribed genes, especially surrounding transcriptional start sites, in embryonic carcinoma NCCIT cells. We also find that C-terminal domain binding or H3K79 methylations by hDOT1L is important for the expression of target genes such as NANOG and OCT4 and a marker for pluripotency in NCCIT cells. Our results indicate that a functional interaction between hDOT1L and RNAPII targets hDOT1L and subsequent H3K79 methylations to actively transcribed genes.

A sheet resistance- and optical transmittance-tunable amorphous ZnSnO3 (ZTO) multilayer electrode created through the insertion of a nano-scale Ag layer is demonstrated as an indium-free transparent conducting electrode for cost-efficient inverted organic solar cells (IOSCs). Due to the antireflection effect, the ZTO/Ag/ZTO/glass exhibited a high transmittance of 86.29% in the absorption wavelength region of the organic active layer and a low resistivity of 3.24×10−5 Ω cm, even though the ZTO/Ag/ZTO electrode was prepared at room temperature. The metallic conductivity of the electrode indicates that its electrical conductivity is dominated by the nano-scale Ag metal layer. In addition, optimization and control of the thickness of the nano-scale Ag layer are important in obtaining highly transparent ZTO/Ag/ZTO electrodes, because antireflection is strongly influenced by Ag thickness. Moreover, IOSCs fabricated on optimized ZTO/Ag/ZTO electrodes with Ag thicknesses of 12 nm showed power conversion efficiencies (2.55%) comparable to that of an IOSC prepared on a crystalline ITO electrode (2.45%), due to the low sheet resistance and high optical transmittance in the range of 400–600 nm. The performances of ZTO/Ag/ZTO multilayer electrodes indicate that ZTO/Ag/ZTO multilayers are promising as indium-free, transparent electrode substitutes for conventional ITO electrodes in cost-efficient IOSCs.