Appearance of iPSCs–Different Reprogramming Stages within the Same Well

From AlleleBlog

Previously scientists at Allele Biotech have reported near uniform conversion of human fibroblasts using our proprietary mRNA mixtures. The first picture below shows a well of cells after 7 days of growing fibroblasts with the new Allele mRNA mix.

This month, by adjusting the mRNA dose while testing Allele’s own reprogramming medium formulation, we observed various stages of cells going through the transition in the same well (see pictures 2 to 5). All stages of reprogramming typically observed over a span of weeks can actually be seen within 1 well of a 6-well plate when we treated human fibroblasts at half the dose of our standard mRNA mix, on day 10, and using Allele Biotech’s new formulation of reprogramming medium.

(1) Warren, Ni, Wang, and Guo 2012 (pdf download)

Previous bulk conversion on Day 7 of reprogramming at full dose mRNA, improved upon our published efficiency (1)

iPSCs forming small colonies from single cells within a 24-hour time frame

Reprogramming en masse: post mesenchymal-to-epithelial (MET) transition cells start to become iPSCs without surrounding fibroblasts (as opposed to the above figure)

Large patches of cells that became iPSCs in what we call bulk-conversion

Large colonies become highly compact, with sharp edges, and composed of mature stem cells of small cell body and tight bundling

Picture Blog: How Do You Like Your iPSCs, Clonal or Bulk-Conversion?

Weekly update on an ongoing NIH project for improving mRNA reprogramming at AlleleBlog

Reprogramming of differentiated cells into induced pluripotent stem cells (iPSCs) is commonly considered a stochastic process, i.e. with randomness, which could offer a convenient excuse for the historical inefficiency and inconstancy of making iPSCs. We have demonstrated time and again that by using potent mRNA cocktails, the majority of the fibroblasts seeded in a well can be converted into pluripotent stage in a nearly synchronized manner (Warren et al. 2012, Warren and Wang 2013, and this Allele Picture Blog series). mRNA molecules can function robustly yet transiently while avoiding the need of entering the nucleus, a bottle-neck for all DNA-based vehicles.

Other researchers are used to the idea of clonal expansion partly because isolating iPSCs from “clones” was a common step during reprogramming using viruses or other low efficiency methods, even though those clones were not necessarily from single precursor cells. This week, the Allele iPSC team developed a new way of managing our mRNA reprogramming that allowed us to achieve clonal iPSCs that appear to be a lot purer and more likely true clones compared to previous reports, without compromising any of the main benefits of our protocol, e.g. feeder-free, xeno-free, footprint-free, very fast and highly efficient. This work is currently supported by an NIDA/NIH grant to Dr. Jiwu Wang at Allele Biotech.

Traditional bulk-conversion by the Allele mRNA reprogramming protocol developed by Warren et al. The picture shows large patches of cells becoming stem cells almost overnight around the 9th day of adding mRNA-cocktail supplement to the media.

Clonal iPSC formation using a modified mRNA reprogramming protocol. The picture shows a typical clone of stem cells that originated from likely single cells.

Warren, Ni, Wang, and Guo, Scientific Reports, 2012
Warren and Wang, Current Protocols, 2013, in press