Generation of a CRISPR/Cas edited human induced pluripotent stem cell line DHMi005-A-1 carrying a patient-specific disease-causing point mutation in the TBX5 gene

The benign nature and rare occurrence of cardiac myxoma as a possible consequence of the limited cardiac proliferative/ regenerative potential: a systematic review

BACKGROUND

Cardiac Myxoma is a primary tumor of heart. Its origins, rarity of the occurrence of primary cardiac tumors and how it may be related to limited cardiac regenerative potential, are not yet entirely known. This study investigates the key cardiac genes/ transcription factors (TFs) and signaling pathways to understand these important questions.

METHODS

Databases including PubMed, MEDLINE, and Google Scholar were searched for published articles without any date restrictions, involving cardiac myxoma, cardiac genes/TFs/signaling pathways and their roles in cardiogenesis, proliferation, differentiation, key interactions and tumorigenesis, with focus on cardiomyocytes.

RESULTS

The cardiac genetic landscape is governed by a very tight control between proliferation and differentiation-related genes/TFs/pathways. Cardiac myxoma originates possibly as a consequence of dysregulations in the gene expression of differentiation regulators including Tbx5, GATA4, HAND1/2, MYOCD, HOPX, BMPs. Such dysregulations switch the expression of cardiomyocytes into progenitor-like state in cardiac myxoma development by dysregulating Isl1, Baf60 complex, Wnt, FGF, Notch, Mef2c and others. The Nkx2-5 and MSX2 contribute predominantly to both proliferation and differentiation of Cardiac Progenitor Cells (CPCs), may possibly serve roles based on the microenvironment and the direction of cell circuitry in cardiac tumorigenesis. The Nkx2-5 in cardiac myxoma may serve to limit progression of tumorigenesis as it has massive control over the proliferation of CPCs. The cardiac cell type-specific genetic programming plays governing role in controlling the tumorigenesis and regenerative potential.

CONCLUSION

The cardiomyocytes have very limited proliferative and regenerative potential. They survive for long periods of time and tightly maintain the gene expression of differentiation genes such as Tbx5, GATA4 that interact with tumor suppressors (TS) and exert TS like effect. The total effect such gene expression exerts is responsible for the rare occurrence and benign nature of primary cardiac tumors. This prevents the progression of tumorigenesis. But this also limits the regenerative and proliferative potential of cardiomyocytes. Cardiac Myxoma develops as a consequence of dysregulations in these key genes which revert the cells towards progenitor-like state, hallmark of CM. The CM development in carney complex also signifies the role of TS in cardiac cells.

Efficient gene editing in induced pluripotent stem cells enabled by an inducible adenine base editor with tunable expression

The preferred method for disease modeling using induced pluripotent stem cells (iPSCs) is to generate isogenic cell lines by correcting or introducing pathogenic mutations. Base editing enables the precise installation of point mutations at specific genomic locations without the need for deleterious double-strand breaks used in the CRISPR-Cas9 gene editing methods. We created a bulk population of iPSCs that homogeneously express ABE8e adenine base editor enzyme under a doxycycline-inducible expression system at the AAVS1 safe harbor locus. These cells enabled fast, efficient and inducible gene editing at targeted genomic regions, eliminating the need for single-cell cloning and screening to identify those with homozygous mutations. We could achieve multiplex genomic editing by creating homozygous mutations in very high efficiencies at four independent genomic loci simultaneously in AAVS1-iABE8e iPSCs, which is highly challenging with previously described methods. The inducible ABE8e expression system allows editing of the genes of interest within a specific time window, enabling temporal control of gene editing to study the cell or lineage-specific functions of genes and their molecular pathways. In summary, the inducible ABE8e system provides a fast, efficient and versatile gene-editing tool for disease modeling and functional genomic studies.