Unknown,Transcriptomics,Genomics,Proteomics

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Early reprogramming stages and regulators identified by prospective isolation and single cell mass cytometry

ABSTRACT: In the context of most induced pluripotent stem (iPS) cell reprogramming methods, heterogeneous populations of nonproductive and staggered productive intermediates arise at different reprogramming time points1-11. Despite recent reports claiming substantially increased reprogramming efficiencies using genetically modified donor cells12,13 prospectively isolating distinct reprogramming intermediates remains an important goal to decipher reprogramming mechanisms. Previous attempts to identify surface markers of intermediate cell populations were based on the assumption that during reprogramming the cells progressively lose donor cell identity and gradually acquire iPS cell properties1,2,7,8,10. Here, we report that iPS cell and epithelial markers, such as SSEA1 and EpCAM, respectively, are not predictive of reprogramming during early phases. Instead, in a systematic functional surface marker screen we find that early reprogramming-prone cells express a unique set of surface markers, including CD73, CD49d and CD200 that are absent in fibroblasts and iPS cells. Single cell mass cytometry and prospective isolation show that these distinct intermediates are transient and bridge the gap between donor cell silencing and pluripotency marker acquisition during the early, presumably stochastic reprogramming phase2. Expression profiling revealed that the transcriptional regulators Nr0b1 and Etv5 are specifically expressed in this early reprogramming state, preceding activation of key pluripotency regulators such as Rex1, Dppa2, Nanog and Sox2. Both factors are required for the generation of the early intermediate state and fully reprogrammed iPS cells, and thus mark some of the earliest known regulators of iPS cell induction. Our study shows an ordered sequence of transitions during the earliest steps of iPS cell reprogramming that deconvolutes the first steps in a hierarchical series of events that lead to pluripotency acquisition. Samples for poised (CD73+ or CD49d+) and non-poised (CD73-) reprogramming samples were FACS sorted 6 and 9 days after induction of Klf4, Oct4, Sox2 and cMyc in Rosa-rtTA +/- mouse embryonic fibroblasts (MEFs). 'Total' populations are expression analyses for unsorted populations analyzed at the same time points. Control populations were also sampled: mouse embryonic fibroblasts (MEFs), partially reprogrammed cells (SC4) and mouse embryonic stem cell (ESC).

ORGANISM(S): Mus musculus

SUBMITTER: Marius Wernig

PROVIDER: E-GEOD-62957 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Direct conversion of fibroblasts to induced cardiomyocytes (iCMs) has great potential for regenerative medicine. Recent publications have reported significant progress, but the evaluation of reprogramming has relied upon non-functional measures such as flow cytometry for cardiomyocyte markers or GFP expression driven by a cardiomyocyte-specific promoter. The issue is one of practicality: the most stringent measures - electrophysiology to detect cell excitation and the presence of spontaneously contracting myocytes - are not readily quantifiable in the large numbers of cells screened in reprogramming experiments. However, excitation and contraction are linked by a third functional characteristic of cardiomyocytes: the rhythmic oscillation of intracellular calcium levels. We set out to optimize direct conversion of fibroblasts to iCMs with a quantifiable calcium reporter to rapidly assess functional transdifferentiation. We constructed a reporter system in which the calcium indicator GCaMP is driven by the cardiomyocyte-specific Troponin T promoter. Using calcium activity as our primary outcome measure, we compared several published combinations of transcription factors along with novel combinations in mouse embryonic fibroblasts. The most effective combination consisted of Hand2, Nkx2.5, Gata4, Mef2c, and Tbx5 (HNGMT). This combination is >50-fold more efficient than GMT alone and produces iCMs with cardiomyocyte marker expression, robust calcium oscillation, and spontaneous beating that persists for weeks following inactivation of reprogramming factors. HNGMT is also significantly more effective than previously published factor combinations for the transdifferentiation of adult mouse cardiac fibroblasts to iCMs. Quantification of calcium function is a convenient and effective means for the identification and evaluation of cardiomyocytes generated by direct reprogramming. Using this stringent outcome measure, we conclude that HNGMT produces iCMs more efficiently than previously published methods. Mouse embryonic fibroblasts were treated with different combinations of transcription factors to drive transdifferentiation to induced cardiomyocytes (iCMs). Putative iCMs were enriched by zeocin selection. Zeocin resistance was conferred to iCMs via the TroponinT-GCaMP5-Zeo lentiviral reporter.

Project description:Reprogramming of somatic cells is a valuable tool to understand the mechanisms of regaining pluripotency and further opens up the possibility to generate patient-specific pluripotent stem cells. Reprogramming of mouse and human somatic cells into pluripotent stem cells, designated as induced pluripotent stem (iPS) cells, has been possible with the expression of the transcription factor quartet Oct4, Sox2, c-Myc, and Klf4. Considering that ectopic expression of c-Myc causes tumourigenicity in offspring and retroviruses themselves can cause insertional mutagenesis, the generation of iPS cells with a minimal number of factors may hasten the clinical application of this approach. Here, we show that adult mouse neural stem cells (NSCs) express higher endogenous levels of Sox2 and c-Myc than ES cells and that exogenous Oct4 together with either Klf4 or c-Myc are sufficient to generate iPS cells from NSCs. These two-factor (2F) iPS cells are similar to embryonic stem cells at the molecular level, contribute to development of the germline, and form chimeras. We propose that, in inducing pluripotency, the number of reprogramming factors can be reduced when using somatic cells that endogenously express appropriate levels of complementing factors. Experiment Overall Design: 8 hybridizations in total. Experiment Overall Design: NSC derived iPS cells by 2 factors (Oct4 and Klf4) in triplicate: Experiment Overall Design: - iPS cell_2F_1 Experiment Overall Design: - iPS cell_2F_2 Experiment Overall Design: - iPS cell_2F_3 Experiment Overall Design: Embryonic Stem cells (ESC) in triplicate: Experiment Overall Design: - ESC_1 Experiment Overall Design: - ESC_2 Experiment Overall Design: - ESC_3 Experiment Overall Design: NSC cultures in duplicates: Experiment Overall Design: - NSC_2 Experiment Overall Design: - NSC_3 Experiment Overall Design: NSC derived iPS cells by 4 factors (Oct4, Sox2, c-Myc and Klf4) in triplicate: Experiment Overall Design: - iPS cell_4F_1 Experiment Overall Design: - iPS cell_4F_2 Experiment Overall Design: - iPS cell_4F_3

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Early reprogramming stages and regulators identified by prospective isolation and single cell mass cytometry

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