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Int J Biol Sci 2011; 7(4):426-439. doi:10.7150/ijbs.7.426 This issue Cite

Research Paper

Medaka tert produces multiple variants with differential expression during differentiation in vitro and in vivo

Feng Rao^1*, Tiansu Wang¹, Mingyou Li¹, Zhendong Li¹, Ni Hong¹, Haobin Zhao^1,3, Yan Yan^1,2, Wenqing Lu¹, Tiansheng Chen¹, Weijia Wang¹, Menghuat Lim¹, Yongming Yuan¹, Ling Liu⁴, Lingbing Zeng⁴, Qiwei Wei⁴, Guijun Guan⁵, Changming Li², Yunhan Hong^{1,4 ✉}

1. Department of Biological Sciences, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260;
2. Division of Bioengineering, School of Chemical and Biomedical Engineering, Nanyang Technological University, 70 Nanyang Drive, Singapore 637457;
3. School of Life Sciences, Huazhong Normal University, Wuhan 430079, China;
4. Yangtze River Fisheries Research Institute, Chinese Academy of Fisheries Sciences, 41 Jianghan Road, Jingzhou City, Hubei 434000, China;
5. National Institute for Basic Biology, Okazaki, Japan
* Present address: The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA

✉ Corresponding author: Prof. Yunhan Hong, Department of Biological Sciences, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260. Fax: +65 6779 2486; Tel: +65 6516 2915; Email: dbshyhedu.sg

Abstract

Embryonic stem (ES) cells have immortality for self-renewal and pluripotency. Differentiated human cells undergo replicative senescence. In human, the telomerase reverse transcriptase (Tert), namely the catalytic subunit of telomerase, exhibits differential expression to regulate telomerase activity governing cellular immortality or senescence, and telomerase activity or tert expression is a routine marker of pluripotent ES cells. Here we have identified the medaka tert gene and determined its expression and telomerase activity in vivo and in vitro. We found that the medaka tert locus produces five variants called terta to terte encoding isoforms TertA to TertE. The longest TertA consists of 1090 amino acid residues and displays a maximum of 34% identity to the human TERT and all the signature motifs of the Tert family. TertB to TertE are novel isoforms and have considerable truncation due to alternative splicing. The terta RNA is ubiquitous in embryos, adult tissues and cell lines, and accompanies ubiquitous telomerase activity in vivo and in vitro as revealed by TRAP assays. The tertb RNA was restricted to the testis, absent in embryos before gastrulation and barely detectable in various cell lines The tertc transcript was absent in undifferentiated ES cells but became evident upon ES cell differentiation, in vivo it was barely detectable in early embryos and became evident when embryogenesis proceeds. Therefore, ubiquitous terta expression correlates with ubiquitous telomerase activity in medaka, and expression of other tert variants appears to delineate cell differentiation in vitro and in vivo.

Keywords: medaka, pluripotency, senescence, telomerase, tert, TRAP

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