Production of High-Titer Lentiviral Particles for Stable Genetic Modification of Mammalian Cells

Wnt dose escalation during the exit from pluripotency identifies tranilast as a regulator of cardiac mesoderm

Wnt signaling is a critical determinant of cell lineage development. This study used Wnt dose-dependent induction programs to gain insights into molecular regulation of stem cell differentiation. We performed single-cell RNA sequencing of hiPSCs responding to a dose escalation protocol with Wnt agonist CHIR-99021 during the exit from pluripotency to identify cell types and genetic activity driven by Wnt stimulation. Results of activated gene sets and cell types were used to build a multiple regression model that predicts the efficiency of cardiomyocyte differentiation. Cross-referencing Wnt-associated gene expression profiles to the Connectivity Map database, we identified the small-molecule drug, tranilast. We found that tranilast synergistically activates Wnt signaling to promote cardiac lineage differentiation, which we validate by in vitro analysis of hiPSC differentiation and in vivo analysis of developing quail embryos. Our study provides an integrated workflow that links experimental datasets, prediction models, and small-molecule databases to identify drug-like compounds that control cell differentiation.

Reprogramming the spleen into a functioning 'liver' in vivo

OBJECTIVE

Liver regeneration remains one of the biggest clinical challenges. Here, we aim to transform the spleen into a liver-like organ via directly reprogramming the splenic fibroblasts into hepatocytes in vivo.

DESIGN

In the mouse spleen, the number of fibroblasts was through silica particles (SiO₂) stimulation, the expanded fibroblasts were converted to hepatocytes (iHeps) by lentiviral transfection of three key transcriptional factors (Foxa3, Gata4 and Hnf1a), and the iHeps were further expanded with tumour necrosis factor-α (TNF-α) and lentivirus-mediated expression of epidermal growth factor (EGF) and hepatocyte growth factor (HGF).

RESULTS

SiO₂ stimulation tripled the number of activated fibroblasts. Foxa3, Gata4 and Hnf1a converted SiO₂-remodelled spleen fibroblasts into 2×10⁶ functional iHeps in one spleen. TNF-α protein and lentivirus-mediated expression of EGF and HGF further enabled the total hepatocytes to expand to 8×10⁶ per spleen. iHeps possessed hepatic functions-such as glycogen storage, lipid accumulation and drug metabolism-and performed fundamental liver functions to improve the survival rate of mice with 90% hepatectomy.

CONCLUSION

Direct conversion of the spleen into a liver-like organ, without cell or tissue transplantation, establishes fundamental hepatic functions in mice, suggesting its potential value for the treatment of end-stage liver diseases.

Optimized protocol for gene editing in adipocytes using CRISPR-Cas9 technology

We present a detailed protocol for gene editing in adipocytes using the CRISPR-Cas technology. This protocol describes sgRNA design, preparation of lentiCRISPR-sgRNA vectors, functional validation of sgRNAs, preparation of lentiviruses, and lentiviruses transduction in adipocytes. Moreover, an optimized method of gene editing using the lentiCRISPRv2 vector expressing two sgRNAs targeting two different genes has also been described. For complete details on the use and execution of this protocol, please refer to Qiu et al. (2020).

Reprogramming roadmap reveals route to human induced trophoblast stem cells

The reprogramming of human somatic cells to primed or naive induced pluripotent stem cells recapitulates the stages of early embryonic development^1-6. The molecular mechanism that underpins these reprogramming processes remains largely unexplored, which impedes our understanding and limits rational improvements to reprogramming protocols. Here, to address these issues, we reconstruct molecular reprogramming trajectories of human dermal fibroblasts using single-cell transcriptomics. This revealed that reprogramming into primed and naive pluripotency follows diverging and distinct trajectories. Moreover, genome-wide analyses of accessible chromatin showed key changes in the regulatory elements of core pluripotency genes, and orchestrated global changes in chromatin accessibility over time. Integrated analysis of these datasets revealed a role for transcription factors associated with the trophectoderm lineage, and the existence of a subpopulation of cells that enter a trophectoderm-like state during reprogramming. Furthermore, this trophectoderm-like state could be captured, which enabled the derivation of induced trophoblast stem cells. Induced trophoblast stem cells are molecularly and functionally similar to trophoblast stem cells derived from human blastocysts or first-trimester placentas⁷. Our results provide a high-resolution roadmap for the transcription-factor-mediated reprogramming of human somatic cells, indicate a role for the trophectoderm-lineage-specific regulatory program during this process, and facilitate the direct reprogramming of somatic cells into induced trophoblast stem cells.

Mouse Hematopoietic Stem Cell Modification and Labelling by Transduction and Tracking Posttransplantation

The tracking of the hematopoietic potential of genetically manipulated fluorescent hematopoietic stem cells (HSC) in the bone marrow (BM) allows the assessment of regulatory processes involved in the re-establishment of hematopoiesis posttransplant. Herein, we describe the means to assess the consequence of expressing specific genes in HSC on their engraftment potential posttransplant.

Generation of Mouse-Induced Pluripotent Stem Cells by Lentiviral Transduction

Terminally differentiated somatic cells can be reprogrammed into an embryonic stem cell-like state by the forced expression of four transcription factors: Oct4, Klf4, Sox2, and c-Myc (OKSM). These so-called induced pluripotent stem (iPS) cells can give rise to any cell type of the body and thus have tremendous potential for many applications in research and regenerative medicine. Herein, we describe (1) a protocol for the generation of iPS cells from mouse embryonic fibroblasts (MEFs) using a doxycycline (Dox)-inducible lentiviral transduction system; (2) the derivation of clonal iPS cell lines; and (3) the characterization of the pluripotent potential of iPS cell lines using alkaline phosphatase staining, flow cytometry, and the teratoma formation assays.