Understanding the Molecular Basis of Heterogeneity in Induced Pluripotent Stem Cells

Abstract

Reprogramming of somatic cells to generate induced pluripotent stem cells (iPSCs) has considerable latency and generates epigenetically distinct partially and fully reprogrammed clones. To understand the molecular basis of reprogramming and to distinguish the partially reprogrammed iPSC clones (pre-iPSCs), we analyzed several of these clones for their molecular signatures. Using a combination of markers that are expressed at different stages of reprogramming, we found that the partially reprogrammed stable clones have significant morphological and molecular heterogeneity in their response to transition to the fully pluripotent state. The pre-iPSCs had significant levels of OCT4 expression but exhibited variable levels of mesenchymal-to-epithelial transition. These novel molecular signatures that we identified would help in using these cells to understand the molecular mechanisms in the late of stages of reprogramming. Although morphologically similar mouse iPSC clones showed significant heterogeneity, the human iPSC clones isolated initially on the basis of morphology were highly homogeneous with respect to the levels of pluripotency.

Embryonic Stem Cells: Keeping Track of the Pluripotent Status

“…The latter reference describes the comparison of mESC, mouse embryonic fibroblasts (MEF), and iPSC derived thereof: after reprogramming, the accompanying morphological changes that the iPSC undergo make them virtually indistinguishable from ESC. Nevertheless, within the population of morphologically similar miPSC colonies, there still appears to be considerable variation in terms of molecular pluripotency, in contrast to hiPSC, which show a much higher homogeneity among the colonies that are selected on analogous morphology [11]. Moreover, true hiPSC colonies have a typical hESC morphology that is very distinct from non-hiPSC colonies, hence morphology can very well serve as a criterion for identifying the real hiPSC colonies.…”