Question

In the production of iPSCs, transcription factors are injected into differentiated cells to induce pluripotency. However, the efficiency of de-differentiation (ie: returning to a stem-cell like state) is typically less than 1%. Give 4 reasons why injecting the transcription factor proteins into the cell may not be enough to lead to pluripotency. Then, choose one of your 4 reasons and give a solution that would solve that problem.

Answer 1

* Most of the somatic cells are terminally differentiated cells. These cells have some of the genes or segments of chromosomes that are either selectively lost or selectively amplifiied. Loss of certain regions of chromosomes or genes lead to inefficient dedifferentiation of cells

* Epigenetic mecanisms such as DNA methylation and histone modifications pose a problem in transcriptional and epigenetic landscape that define the pluripotent stem cells. The modifications are barriers to the reprogramming process of dedifferentiation

* Reprogramming (or dedifferentiation) activates DNA damage response pathway, which activates p⁵³ or p²¹genes, which lead to apoptosis or programmed cell death. The process of reporgramming induce stress on cells and this activates stress related DNA damage response.

* Trimethylation of H3K9me3, imprinted genes, constitutive heterochromatin prevent reprogramming of cells

Suggested solutions: Knockdown of p⁵³ and p²¹, inhibition of DNA methylation using inhibitors like 5-azacytidine, ow downregulation of DNA methyltransferease increases reprogramming of cells