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Establishment of transgene-free induced pluripotent stem cells reprogrammed from human stem cells of apical papilla for neural differentiation

Xiao-Ying Zou12, Hsiao-Ying Yang1, Zongdong Yu3, Xiao-Bing Tan14, Xing Yan15 and George T-J Huang13*

Author Affiliations

1 Department of Endodontics, Boston University Henry M. Goldman School of Dental Medicine, Boston, MA 02118, USA

2 Department of Cariology, Endodontology and Operative Dentistry, School and Hospital of Stomatology, Peking University, Beijing, 100081, P. R. China

3 Department of Bioscience Research, College of Dentistry, University of Tennessee Health Science Center. Memphis, TN, USA

4 Department of Stomatology, 1st People's Hospital of Yunnan Province, Kunming, Yunnan, 650032, P. R. China

5 Department of Stomatology, Beijing Friendship Hospital (Second Clinical School), Capital Medical University, Beijing 100050, P.R. China

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Stem Cell Research & Therapy 2012, 3:43  doi:10.1186/scrt134

Published: 24 October 2012

Abstract

Introduction

Induced pluripotent stem cells (iPSCs) are a potent cell source for neurogenesis. Previously we have generated iPSCs from human dental stem cells carrying transgene vectors. These exogenous transgenes may affect iPSC behaviors and limit their clinical applications. The purpose of this study was to establish transgene-free iPSCs (TF-iPSCs) reprogrammed from human stem cells of apical papilla (SCAP) and determine their neurogenic potential.

Methods

A single lentiviral 'stem cell cassette' flanked by the loxP site (hSTEMCCA-loxP), encoding four human reprogramming factors, OCT4, SOX2, KLF4, and c-MYC, was used to reprogram human SCAP into iPSCs. Generated iPSCs were transfected with plasmid pHAGE2-EF1α-Cre-IRES-PuroR and selected with puromycin for the TF-iPSC subclones. PCR was performed to confirm the excision of hSTEMCCA. TF-iPSC clones did not resist to puromycin treatment indicating no pHAGE2-EF1α-Cre-IRES-PuroR integration into the genome. In vitro and in vivo analyses of their pluripotency were performed. Embryoid body-mediated neural differentiation was undertaken to verify their neurogenic potential.

Results

TF-SCAP iPSCs were generated via a hSTEMCCA-loxP/Cre system. PCR of genomic DNA confirmed transgene excision and puromycin treatment verified the lack of pHAGE2-EF1α-Cre-IRES-PuroR integration. Transplantation of the TF-iPSCs into immunodeficient mice gave rise to teratomas containing tissues representing the three germ layers -- ectoderm (neural rosettes), mesoderm (cartilage and bone tissues) and endoderm (glandular epithelial tissues). Embryonic stem cell-associated markers TRA-1-60, TRA-2-49 and OCT4 remained positive after transgene excision. After neurogenic differentiation, cells showed neural-like morphology expressing neural markers nestin, βIII-tubulin, NFM, NSE, NeuN, GRM1, NR1 and CNPase.

Conclusions

TF-SCAP iPSCs reprogrammed from SCAP can be generated and they may be a good cell source for neurogenesis.