Cellular reprogramming by transcription factor engineering

Engineering mouse cell fate controller by rational design

Cell fate is likely regulated by a common machinery, while components of this machine remain to be identified. Here we report the design and testing of engineered cell fate controller NanogBiD, fusing BiD or BRG1 interacting domain of SS18 with Nanog. NanogBiD promotes mouse somatic cell reprogramming efficiently in contrast to the ineffective native protein under multiple testing conditions. Mechanistic studies further reveal that it facilitates cell fate transition by recruiting the intended Brg/Brahma-associated factor (BAF) complex to modulate chromatin accessibility and reorganize cell state specific enhancers known to be occupied by canonical Nanog, resulting in precocious activation of multiple genes including Sall4, miR-302, Dppa5a and Sox15 towards pluripotency. Although we have yet to test our approach in other species, our findings suggest that engineered chromatin regulators may provide much needed tools to engineer cell fate in the cells as drugs era.

Structurally-discovered KLF4 variants accelerate and stabilize reprogramming to pluripotency

Non-genetically modified somatic cells can only be inefficiently and stochastically reprogrammed to pluripotency by exogenous expression of reprogramming factors. Low competence of natural reprogramming factors may prevent the majority of cells to successfully and synchronously reprogram. Here we screened DNA-interacting amino acid residues in the zinc-finger domain of KLF4 for enhanced reprogramming efficiency using alanine-substitution scanning methods. Identified KLF4 L507A mutant accelerated and stabilized reprogramming to pluripotency in both mouse and human somatic cells. By testing all the variants of L507 position, variants with smaller amino acid residues in the KLF4 L507 position showed higher reprogramming efficiency. L507A bound more to promoters or enhancers of pluripotency genes, such as KLF5, and drove gene expression of these genes during reprogramming. Molecular dynamics simulations predicted that L507A formed additional interactions with DNA. Our study demonstrates how modifications in amino acid residues of DNA-binding domains enable next-generation reprogramming technology with engineered reprogramming factors.

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KLF4 L507A variant accelerates and stabilizes reprogramming to pluripotency

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KLF4 L507A has distinctive features of transcriptional binding and activation

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KLF4 L507A may acquire a unique conformation with additional DNA interaction

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Smaller amino acid residues in L507 position cause higher reprogramming efficiency

Advances in reprogramming-based study of neurologic disorders

The technology to convert adult human non-neural cells into neural lineages, through induced pluripotent stem cells (iPSCs), somatic cell nuclear transfer, and direct lineage reprogramming or transdifferentiation has progressed tremendously in recent years. Reprogramming-based approaches aimed at manipulating cellular identity have enormous potential for disease modeling, high-throughput drug screening, cell therapy, and personalized medicine. Human iPSC (hiPSC)-based cellular disease models have provided proof of principle evidence of the validity of this system. However, several challenges remain before patient-specific neurons produced by reprogramming can provide reliable insights into disease mechanisms or be efficiently applied to drug discovery and transplantation therapy. This review will first discuss limitations of currently available reprogramming-based methods in faithfully and reproducibly recapitulating disease pathology. Specifically, we will address issues such as culture heterogeneity, interline and inter-individual variability, and limitations of two-dimensional differentiation paradigms. Second, we will assess recent progress and the future prospects of reprogramming-based neurologic disease modeling. This includes three-dimensional disease modeling, advances in reprogramming technology, prescreening of hiPSCs and creating isogenic disease models using gene editing.

Bacterial-induced cell reprogramming to stem cell-like cells: new premise in host-pathogen interactions

Bacterial pathogens employ a myriad of strategies to alter host tissue cell functions for bacterial advantage during infection. Recent advances revealed a fusion of infection biology with stem cell biology by demonstrating developmental reprogramming of lineage committed host glial cells to progenitor/stem cell-like cells by an intracellular bacterial pathogen Mycobacterium leprae. Acquisition of migratory and immunomodulatory properties of such reprogrammed cells provides an added advantage for promoting bacterial spread. This presents a previously unseen sophistication of cell manipulation by hijacking the genomic plasticity of host cells by a human bacterial pathogen. The rationale for such extreme fate conversion of host cells may be directly linked to the exceedingly passive obligate life style of M. leprae with a degraded genome and host cell dependence for both bacterial survival and dissemination, particularly the use of host-derived stem cell-like cells as a vehicle for spreading infection without being detected by immune cells. Thus, this unexpected link between cell reprogramming and infection opens up a new premise in host-pathogen interactions. Furthermore, such bacterial ingenuity could also be harnessed for developing natural ways of reprogramming host cells for repairing damaged tissues from infection, injury and diseases.