Somatic cells can be reprogrammed to induced pluripotent stem cells (iPSCs) by expression of defined embryonic factors. However, little is known of the molecular mechanisms underlying the reprogramming process. Here we explore somatic cell reprogramming by exploiting a secondary mouse embryonic fibroblast model that forms iPSCs with high efficiency upon inducible expression of Oct4, Klf4, c-Myc, and Sox2. Temporal analysis of gene expression revealed that reprogramming is a multistep process that is characterized by initiation, maturation, and stabilization phases. Functional analysis by systematic RNAi screening further uncovered a key role for BMP signaling and the induction of mesenchymal-to-epithelial transition (MET) during the initiation phase. We show that this is linked to BMP-dependent induction of miR-205 and the miR-200 family of microRNAs that are key regulators of MET. These studies thus define a multistep mechanism that incorporates a BMP-miRNA-MET axis during somatic cell reprogramming. PAPERCLIP:

Functional genomics reveals a bmp driven mesenchymal-to-epithelial transition in the initiation of somatic cell reprogramming (oral presentation)

Facilitators and Impediments of the Pluripotency Reprogramming Factors' Initial Engagement with the Genome

Pioneer transcription factors target partial DNA motifs on nucleosomes to initiate reprogramming

The generation of induced pluripotent stem cells (iPSCs) provides the opportunity to use patient-specific somatic cells, which are a valuable source for disease modeling and drug discovery. To promote research involving these cells, it is important to make iPSCs from easily accessible and less invasive tissues, like blood. We have recently reported the efficient generation of human iPSCs from adult fibroblasts using a combination of plasmids encoding OCT3/4, SOX2, KLF4, L-MYC, LIN28, and shRNA for TP53. We herein report a modified protocol enabling efficient iPSC induction from CD34+ cord blood cells and from peripheral blood isolated from healthy donors using these plasmid vectors. The original plasmid mixture could induce iPSCs; however, the efficiency was low. The addition of EBNA1, an essential factor for episomal amplification of the vectors, by an extra plasmid greatly increased the efficiency of iPSC induction, especially when the induction was performed from αβT cells. This improvement enabled the establishment of blood-derived iPSCs from seven healthy donors ranging in age from their 20s to their 60s. This induction method will be useful for the derivation of patient-specific integration-free iPSCs and would also be applicable to the generation of clinical-grade iPSCs in the future.

https://stemcellsjournals.onlinelibrary.wiley.com/doi/epdf/10.1002/stem.1293

An Efficient Nonviral Method to Generate Integration-Free Human-Induced Pluripotent Stem Cells from Cord Blood and Peripheral Blood Cells†‡§

Conversion of somatic cells to pluripotency by defined factors is a long and complex process that yields embryonic-stem-cell-like cells that vary in their developmental potential. To improve the quality of resulting induced pluripotent stem cells (iPSCs), which is important for potential therapeutic applications, and to address fundamental questions about control of cell identity, molecular mechanisms of the reprogramming process must be understood. Here we discuss recent discoveries regarding the role of reprogramming factors in remodelling the genome, including new insights into the function of MYC, and describe the different phases, markers and emerging models of reprogramming.

/pdf/mechanisms-and-models-of-somatic-cell-reprogramming-54dwxv305y.pdf

Mechanisms and models of somatic cell reprogramming

Reprogramming of differentiated somatic cells to induced pluripotent stem (iPS) cells by exogenous expression of key transcription factors (Oct4, Sox2, Klf4 and c-Myc) has potential therapeutic applications. c-Myc enhances the efficiency of reprogramming, but the safety of using this oncogene has long been a concern. Now, Shinya Yamanaka and colleagues have found that the transcription factor Glis1 effectively and specifically promotes reprogramming of human and mouse somatic cells to iPS cells. Glis1 is highly enriched in unfertilized eggs and one-cell-stage embryos, and might be a link between reprogramming during iPS cell generation and after nuclear transfer into zygotes. Induced pluripotent stem cells (iPSCs) are generated from somatic cells by the transgenic expression of three transcription factors collectively called OSK: Oct3/4 (also called Pou5f1), Sox2 and Klf41. However, the conversion to iPSCs is inefficient. The proto-oncogene Myc enhances the efficiency of iPSC generation by OSK but it also increases the tumorigenicity of the resulting iPSCs2. Here we show that the Gli-like transcription factor Glis1 (Glis family zinc finger 1) markedly enhances the generation of iPSCs from both mouse and human fibroblasts when it is expressed together with OSK. Mouse iPSCs generated using this combination of transcription factors can form germline-competent chimaeras. Glis1 is enriched in unfertilized oocytes and in embryos at the one-cell stage. DNA microarray analyses show that Glis1 promotes multiple pro-reprogramming pathways, including Myc, Nanog, Lin28, Wnt, Essrb and the mesenchymal–epithelial transition. These results therefore show that Glis1 effectively promotes the direct reprogramming of somatic cells during iPSC generation.

/pdf/direct-reprogramming-of-somatic-cells-is-promoted-by-53ht4mm99q.pdf

Direct reprogramming of somatic cells is promoted by maternal transcription factor Glis1

Cationic peptides termed protein transduction domains (PTDs) have been shown to cross biological membranes efficiently. However, proteins transduced by PTDs become entrapped within the endosomal vesicles and are not delivered into organelles. We have developed a novel protein delivery system to enhance the proton sponge effect, which results in rupture of the endosomes, by using a mixture of Wr-T transporter peptide and a commercially available cationic lipid reagent. This peptide and cationic lipid reagent mixture efficiently delivers a variety of cargo proteins into living cells by releasing them from the endosomes.

/pdf/efficient-protein-transduction-method-using-cationic-3tsiqlpqrr.pdf

Efficient Protein Transduction Method Using Cationic Peptides and Lipids

TRA98 is a rat monoclonal antibody (mAb) which recognizes a specific antigen in the nuclei of germ cells. mAb TRA98 has been used to understand the mechanism of germ cell development and differentiation in many studies. In mice, the antigen recognized by mAb TRA98 or GCNA1 has been reported to be a GCNA gene product, but despite the demonstration of the immunoreactivity of this mAb in human testis and sperm in 1997, the antigen in humans remains unknown, as of date. To identify the human antigen recognized by mAb TRA98, a human comprehensive wet protein array was developed containing 19,446 proteins derived from human cDNAs. Using this array, it was found that the antigen of mAb TRA98 is not a GCNA gene product, but nuclear factor-κB activating protein (NKAP). In mice, mAb TRA98 recognized both the GCNA gene product and NKAP. Furthermore, conditional knockout of Nkap in mice revealed a phenotype of Sertoli cell-only syndrome. Although NKAP is a ubiquitously expressed protein, NKAP recognized by mAb TRA98 in mouse testis was SUMOylated. These results suggest that NKAP undergoes modifications, such as SUMOylation in the testis, and plays an important role in spermatogenesis.

Identification and characterization of the antigen recognized by the germ cell mAb TRA98 using a human comprehensive wet protein array.

Thrombopoietin (THPO) is a circulatory cytokine that plays an important role in platelet production. The presence of anti-THPO antibody relates to thrombocytopenia and is rarely seen in hematopoietic and autoimmune diseases. To date, there had been no reports that focused on the anti-THPO antibody in patients with type 2 diabetes mellitus (T2DM). To evaluate prevalence of the anti-THPO antibody in patients with T2DM and the relationship between anti-THPO antibody and platelet count, a cross-sectional study was performed on 82 patients with T2DM. The anti-THPO antibody was measured by ELISA using preserved sera and detected in 13 patients. The average platelet count was significantly lower in patients with the anti-THPO antibody than in those without the anti-THPO antibody. Multivariate linear regression analyses showed a significant relationship between the anti-THPO antibody and platelet count, after adjusting for other variables. To our best knowledge, this was the first report on the effect of the anti-THPO antibody on platelet count in patients with T2DM. Further investigation is needed to validate the prevalence and pathological significance of the anti-THPO antibody in patients with T2DM.

https://www.mdpi.com/1420-3049/25/7/1667/pdf

Kei Yamaguchi

Papers

Direct reprogramming of somatic cells is promoted by maternal transcription factor Glis1

Efficient Protein Transduction Method Using Cationic Peptides and Lipids

Identification and characterization of the antigen recognized by the germ cell mAb TRA98 using a human comprehensive wet protein array.

A Pilot Study on the Effect of Anti-Thrombopoietin Antibody on Platelet Count in Patients with Type 2 Diabetes