Research Article Mesenchymal to embryonic incomplete transition of human cells by chimeric OCT4/3 (POU5F1) with physiological co-activator EWS Hatsune Makino a , Masashi Toyoda a , Kenji Matsumoto b , Hirohisa Saito b , Koichiro Nishino a , Yoshihiro Fukawatase a , Masakazu Machida a , Hidenori Akutsu a , Taro Uyama a , Yoshitaka Miyagawa c , Hajime Okita c , Nobutaka Kiyokawa c , Takashi Fujino d,f , Yuichi Ishikawa e , Takuro Nakamura d , Akihiro Umezawa a, ⁎ a Department of Reproductive Biology, National Institute for Child Health and Development, Tokyo,157-8535, Japan b Department of Allergy and Immunology, National Institute for Child Health and Development, Tokyo,157-8535, Japan c Department of Developmental Biology and Pathology, National Institute for Child Health and Development, Tokyo,157-8535, Japan d Department of Carcinogenesis, The Cancer Institute, Japanese Foundation for Cancer Research, Tokyo, 140-8455, Japan e Department of Pathology, The Cancer Institute, Japanese Foundation for Cancer Research, Tokyo,140-8455, Japan f Department of Pathology, Faculty of Medicine, Kyorin University, Tokyo, 181-8611, Japan ARTICLEINFORMATION ABSTRACT Article Chronology: Received 7 November 2008 Revised version received 15 June 2009 Accepted 16 June 2009 Available online 24 June 2009 POU5F1 (more commonly known as OCT4/3) is one of the stem cell markers, and affects direction of differentiation in embryonic stem cells. To investigate whether cells of mesenchymal origin acquire embryonic phenotypes, we generated human cells of mesodermal origin with overexpression of the chimeric OCT4/3 gene with physiological co-activator EWS (product of the EWSR1 gene), which is driven by the potent EWS promoter by translocation. The cells expressed embryonic stem cell genes such as NANOG, lost mesenchymal phenotypes, and exhibited embryonal stem cell-like alveolar structures when implanted into the subcutaneous tissue of immunodeficient mice. Hierarchical analysis by microchip analysis and cell surface analysis revealed that the cells are subcategorized into the group of human embryonic stem cells and embryonal carcinoma cells. These results imply that cells of mesenchymal origin can be traced back to cells of embryonic phenotype by the OCT4/3 gene in collaboration with the potent cis-regulatory element and the fused co-activator. The cells generated in this study with overexpression of chimeric OCT4/3 provide us with insight into cell plasticity involving OCT4/3 that is essential for embryonic cell maintenance, and the complexity required for changing cellular identity. © 2009 Elsevier Inc. All rights reserved. Keywords: Dedifferentiation Mesoderm Embryonic carcinoma iPS cell OCT4/3 Stem cell Introduction Somatic stem cells have been shown to have a more flexible poten- tial, but the conversion of mesenchymal cells to embryonic stem (ES) cells has still been a challenge and requires gene transduction [1–4]. This phenotypic conversion requires the molecular repro- gramming of mesenchyme. Mesenchymal stem cells or mesenchy- mal progenitors have been isolated from adult bone marrow [5], adipose tissue [6], dermis [7], endometrium [8], menstrual blood [8], cord blood [9,10], and other connective tissues [11]. These cells are EXPERIMENTAL CELL RESEARCH 315 (2009) 2727 – 2740 ⁎ Corresponding author. Fax: +81 3 5494 7048. E-mail address: umezawa@1985.jukuin.keio.ac.jp (A. Umezawa). 0014-4827/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.yexcr.2009.06.016 available at www.sciencedirect.com www.elsevier.com/locate/yexcr