Induction of human pluripotent stem cells into kidney tissues by synthetic mRNAs encoding transcription factors

The derivation of kidney tissues from human pluripotent stem cells (hPSCs) and its application for replacement therapy in end-stage renal disease have been widely discussed. Here we report that consecutive transfections of two sets of synthetic mRNAs encoding transcription factors can induce rapid and efficient differentiation of hPSCs into kidney tissues, termed induced nephron-like organoids (iNephLOs). The first set - FIGLA, PITX2, ASCL1 and TFAP2C, differentiated hPSCs into SIX2+SALL1+ nephron progenitor cells with 92% efficiency within 2 days. Subsequently, the second set - HNF1A, GATA3, GATA1 and EMX2, differentiated these cells into PAX8+LHX1+ pretubular aggregates in another 2 days. Further culture in both 2-dimensional and 3-dimensional conditions produced iNephLOs containing cells characterized as podocytes, proximal tubules, and distal tubules in an additional 10 days. Global gene expression profiles showed similarities between iNephLOs and the human adult kidney, suggesting possible uses of iNephLOs as in vitro models for kidneys.

Establishment of a rapid and footprint-free protocol for differentiation of human embryonic stem cells into pancreatic endocrine cells with synthetic mRNAs encoding transcription factors

BACKGROUND

Transplantation of pancreatic β cells generated in vitro from pluripotent stem cells (hPSCs) such as embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs) has been proposed as an alternative therapy for diabetes. Though many differentiation protocols have been developed for this purpose, lentivirus-mediated forced expression of transcription factors (TF)-PDX1 and NKX6.1-has been at the forefront for its relatively fast and straightforward approach. However, considering that such cells will be used for therapeutic purposes in the future, it is desirable to develop a procedure that does not leave any footprint on the genome, as any changes of DNAs could potentially be a source of unintended, concerning effects such as tumorigenicity. In this study, we attempted to establish a novel protocol for rapid and footprint-free hESC differentiation into a pancreatic endocrine lineage by using synthetic mRNAs (synRNAs) encoding PDX1 and NKX6.1. We also tested whether siPOU5F1, which reduces the expression of pluripotency gene POU5F1 (also known as OCT4), can enhance differentiation as reported previously for mesoderm and endoderm lineages.

METHODS

synRNA-PDX1 and synRNA-NKX6.1 were synthesized in vitro and were transfected five times to hESCs with a lipofection reagent in a modified differentiation culture condition. siPOU5F1 was included only in the first transfection. Subsequently, cells were seeded onto a low attachment plate and aggregated by an orbital shaker. At day 13, the degree of differentiation was assessed by quantitative RT-PCR (qRT-PCR) and immunohistochemistry for endocrine hormones such as insulin, glucagon, and somatostatin.

RESULTS

Both PDX1 and NKX6.1 expression were detected in cells co-transfected with synRNA-PDX1 and synRNA-NKX6.1 at day 3. Expression levels of insulin in the transfected cells at day 13 were 450 times and 14 times higher by qRT-PCR compared to the levels at day 0 and in cells cultured without synRNA transfection, respectively. Immunohistochemically, pancreatic endocrine hormones were not detected in cells cultured without synRNA transfection but were highly expressed in cells transfected with synRNA-PDX1, synRNA-NKX6.1, and siPOU5F1 at as early as day 13.

CONCLUSIONS

In this study, we report a novel protocol for rapid and footprint-free differentiation of hESCs to endocrine cells.

Efficient differentiation of human pluripotent stem cells into skeletal muscle cells by combining RNA-based MYOD1-expression and POU5F1-silencing

Direct generation of skeletal muscle cells from human pluripotent stem cells (hPSCs) would be beneficial for drug testing, drug discovery, and disease modelling in vitro. Here we show a rapid and robust method to induce myogenic differentiation of hPSCs by introducing mRNA encoding MYOD1 together with siRNA-mediated knockdown of POU5F1 (also known as OCT4 or OCT3/4). This integration-free approach generates functional skeletal myotubes with sarcomere-like structure and a fusion capacity in several days. The POU5F1 silencing facilitates MYOD1 recruitment to the target promoters, which results in the significant activation of myogenic genes in hPSCs. Furthermore, deep sequencing transcriptome analyses demonstrated that POU5F1-knockdown upregulates the genes associated with IGF- and FGF-signaling and extracellular matrix that may also support myogenic differentiation. This rapid and direct differentiation method may have potential applications in regenerative medicine and disease therapeutics for muscle disorders such as muscular dystrophy.

Neural differentiation of human embryonic stem cells induced by the transgene-mediated overexpression of single transcription factors

Pluripotent human embryonic stem cells (hESCs) can differentiate into multiple cell lineages, thus, providing one of the best platforms to study molecular mechanisms during cell differentiation. Recently, we have reported rapid and efficient differentiation of hESCs into functional neurons by introducing a cocktail of synthetic mRNAs encoding five transcription factors (TFs): NEUROG1, NEUROG2, NEUROG3, NEUROD1, and NEUROD2. Here we further tested a possibility that even single transcription factors, when expressed ectopically, can differentiate hESCs into neurons. To this end, we established hESC lines in which each of these TFs can be overexpressed by the doxycycline-inducible piggyBac vector. The overexpression of any of these five TFs indeed caused a rapid and rather uniform differentiation of hESCs, which were identified as neurons based on their morphologies, qRT-PCR, and immunohistochemistry. Furthermore, calcium-imaging analyses and patch clamp recordings demonstrated that these differentiated cells are electrophysiologically functional. Interestingly, neural differentiations occurred despite the cell culture conditions that rather promote the maintenance of the undifferentiated state. These results indicate that over-expression of each of these five TFs can override the pluripotency-specific gene network and force hESCs to differentiate into neurons.

Identification of transcription factors that promote the differentiation of human pluripotent stem cells into lacrimal gland epithelium-like cells

Dry eye disease is the most prevalent pathological condition in aging eyes. One potential therapeutic strategy is the transplantation of lacrimal glands, generated in vitro from pluripotent stem cells such as human embryonic stem cells, into patients. One of the preceding requirements is a method to differentiate human embryonic stem cells into lacrimal gland epithelium cells. As the first step for this approach, this study aims to identify a set of transcription factors whose overexpression can promote the differentiation of human embryonic stem cells into lacrimal gland epithelium-like cells. We performed microarray analyses of lacrimal glands and lacrimal glands-related organs obtained from mouse embryos and adults, and identified transcription factors enriched in lacrimal gland epithelium cells. We then transfected synthetic messenger RNAs encoding human orthologues of these transcription factors into human embryonic stem cells and examined whether the human embryonic stem cells differentiate into lacrimal gland epithelium-like cells by assessing cell morphology and marker gene expression. The microarray analysis of lacrimal glands tissues identified 16 transcription factors that were enriched in lacrimal gland epithelium cells. We focused on three of the transcription factors, because they are expressed in other glands such as salivary glands and are also known to be involved in the development of lacrimal glands. We tested the overexpression of various combinations of the three transcription factors and PAX6, which is an indispensable gene for lacrimal glands development, in human embryonic stem cells. Combining PAX6, SIX1, and FOXC1 caused significant changes in morphology, i.e., elongated cell shape and increased expression (both RNAs and proteins) of epithelial markers such as cytokeratin15, branching morphogenesis markers such as BARX2, and lacrimal glands markers such as aquaporin5 and lactoferrin. We identified a set of transcription factors enriched in lacrimal gland epithelium cells and demonstrated that the simultaneous overexpression of these transcription factors can differentiate human embryonic stem cells into lacrimal gland epithelium-like cells. This study suggests the possibility of lacrimal glands regeneration from human pluripotent stem cells.

Transient ectopic expression of the histone demethylase JMJD3 accelerates the differentiation of human pluripotent stem cells

Harnessing epigenetic regulation is crucial for the efficient and proper differentiation of pluripotent stem cells (PSCs) into desired cell types. Histone H3 lysine 27 trimethylation (H3K27me3) functions as a barrier against cell differentiation through the suppression of developmental gene expression in PSCs. Here, we have generated human PSC (hPSC) lines in which genome-wide reduction of H3K27me3 can be induced by ectopic expression of the catalytic domain of the histone demethylase JMJD3 (called JMJD3c). We found that transient, forced demethylation of H3K27me3 alone triggers the upregulation of mesoendodermal genes, even when the culture conditions for the hPSCs are not changed. Furthermore, transient and forced expression of JMJD3c followed by the forced expression of lineage-defining transcription factors enabled the hPSCs to activate tissue-specific genes directly. We have also shown that the introduction of JMJD3c facilitates the differentiation of hPSCs into functional hepatic cells and skeletal muscle cells. These results suggest the utility of the direct manipulation of epigenomes for generating desired cell types from hPSCs for cell transplantation therapy and platforms for drug screenings.

Zscan4 is expressed specifically during late meiotic prophase in both spermatogenesis and oogenesis

Mouse zinc finger and SCAN domain containing 4 (Zscan4) proteins, which are encoded by multiple copies of Zscan4 genes, are expressed specifically in preimplantation embryos in vivo and embryonic stem (ES) cells in vitro. However, the expression patterns of mouse Zscan4 in vivo have been largely elusive. Here, we show that Zscan4 proteins are expressed in adult ovaries and testes. In ovaries, Zscan4 proteins were detected in germinal vesicle (GV) stage oocytes in antral follicles, indicating that Zscan4 genes are activated during the diplotene/dictyate stage in meiotic prophase I. Remarkably, Zscan4 showed different spatial localization patterns between two distinct GV oocytes, which can be distinguished by global chromatin organization—surrounded nucleolus (SN) and non-surrounded nucleolus (NSN). These spatiotemporal differences in Zscan4 localizations correlated with the transition of RNA polymerase II-mediated transcriptional status during GV oocyte maturation. In testes, Zscan4 proteins were detected in spermatocytes at late pachytene/diplotene stages and in Sertoli cells. These results suggest that Zscan4 may play critical roles during late meiotic prophase in both males and females.