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Reprogramming Revealed Using a Mass-terly Strategy

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Review of “Early reprogramming regulators identified by prospective isolation and mass cytometry” from Nature by Stuart P. Atkinson

While much time and effort has been poured into the study of the generation of induced pluripotent stem cells (iPSCs), we are still trying to delineate the complex mechanisms which lie behind the early stochastic and late deterministic phases which are assumed to occur [1-3]. In a new study, and using a new strategy, the laboratory of Marius Wernig (Stanford University) have implemented a mass cytometry approach to the study of reprogramming, and have unveiled some interesting new findings [4].

The use of a mass cytometry-based assessment allowed the group to initially screen 176 antibodies on cells representing the breadth of the reprogramming process; donor cells (mouse embryonic fibroblasts), an intermediate (partially reprogrammed cell), and the eventual reprogramming target (mouse iPSCs). Surprisingly, their initial findings found that the acquisition of pluripotency markers and the loss of fibroblast markers are actually late events and do not predict for the success of the reprogramming process. Instead they found that partially reprogrammed cells likely to form fully reprogrammed iPSCs expressed the cell surface markers CD73, CD49d and CD200, and these cells represented an intermediate stage between somatic cell identity silencing and the acquisition of pluripotency. Using these markers, the group selected and analyzed this reprogramming-prone population to understand transcriptional regulatory networks which are predominant at this stage. This highlighted important roles for the transcription factors Nr0b1 and Etv5 and the knockdown of these genes in fibroblasts severely inhibited the reprogramming process, although knockdown in ESCs had not effect on survival or proliferation.

This study represents an important step forward in the understanding of the chaotic early stages of reprogramming and could impact iPSC production in two important ways. Firstly the generation of new reprogramming techniques utilizing the newly identified transcription factors and secondly the implementation of screens using the surface markers identified to select only for those few cells with the capacity to become iPSCs. This would increase efficiency and reduce costs, and if this is translatable to human iPSC production, may make this highly utile cell population even more clinically relevant.

References

  1. Buganim Y, Faddah DA, Cheng AW, et al. Single-cell expression analyses during cellular reprogramming reveal an early stochastic and a late hierarchic phase. Cell 2012;150:1209-1222.
  2. Golipour A, David L, Liu Y, et al. A late transition in somatic cell reprogramming requires regulators distinct from the pluripotency network. Cell Stem Cell 2012;11:769-782.
  3. Hanna J, Saha K, Pando B, et al. Direct cell reprogramming is a stochastic process amenable to acceleration. Nature 2009;462:595-601.
  4. Lujan E, Zunder ER, Ng YH, et al. Early reprogramming regulators identified by prospective isolation and mass cytometry. Nature 2015. [Epub ahead of print]