Vol 16, No 1 ,2015, African Scientist

The pluripotency of embryonic stem (ES) cells is the result of a highly dynamic equilibrium that is controlled by a complex network of transcription factors that confer unique transcriptional properties to ES cells. Regulation of gene expression appears to correlate with the presence of dual chromatin marks called bivalent domains at the promoters of poised developmental genes. These marks keep differentiation genes silenced but poised and ready to be activated or permanently repressed during differentiation.

The directed differentiation of human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hiPSCs) into hepatocytes could facilitate a rational study of the molecular mechanisms underlying human liver development as well as provide a renewable source of exogenous hepatocytes for drug toxicity testing and cell-based therapeutics. Moreover, if hepatocytes were produced from hiPSCs originating from patients with inborn errors of hepatic metabolism, such cells could be used for modeling liver disease.

Prolonged culture of pluripotent and multipotent stem cells exposes the cells to strong selection pressures, often resulting in genomic alterations. Any genetic manipulation of the cells may further jeopardize their genomic stability. Genomic aberrations affect the differentiation capacity of stem cells, their stem cell identity and their tumorigenicity, and should thus be routinely evaluated for their proper use in basic research and in clinical trials.

Genome editing is used to make targeted modifications to the genome of eukaryotic cells. There are many potential applications of genome editing in human pluripotent stem cells (hPSCs) including the generation of knockout and reporter cell lines. This protocol describes a system for efficient genome editing in hPSCs using engineered transcription activator-like effector nucleases (TALENs) or clustered regularly interspaced short palindromic repeat (CRISPR) technology.