Single-cell imaging reveals unexpected heterogeneity of telomerase reverse transcriptase expression across human cancer cell lines

Proc Natl Acad Sci U S A. 2019 Sep 10;116(37):18488-18497. doi: 10.1073/pnas.1908275116. Epub 2019 Aug 26.


Telomerase is pathologically reactivated in most human cancers, where it maintains chromosomal telomeres and allows immortalization. Because telomerase reverse transcriptase (TERT) is usually the limiting component for telomerase activation, numerous studies have measured TERT mRNA levels in populations of cells or in tissues. In comparison, little is known about TERT expression at the single-cell and single-molecule level. To address this, we analyzed TERT expression across 10 human cancer lines using single-molecule RNA fluorescent in situ hybridization (FISH) and made several unexpected findings. First, there was substantial cell-to-cell variation in number of transcription sites and ratio of transcription sites to gene copies. Second, previous classification of lines as having monoallelic or biallelic TERT expression was found to be inadequate for capturing the TERT gene expression patterns. Finally, spliced TERT mRNA had primarily nuclear localization in cancer cells and induced pluripotent stem cells (iPSCs), in stark contrast to the expectation that spliced mRNA should be predominantly cytoplasmic. These data reveal unappreciated heterogeneity, complexity, and unconventionality in TERT expression across human cancer cells.

Keywords: TERT; cancer; single-molecule imaging; telomerase; transcription.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Cell Line, Tumor
  • Cell Nucleus / enzymology
  • Cell Nucleus / genetics
  • Cytoplasm / enzymology
  • Cytoplasm / genetics
  • Gene Expression Regulation, Enzymologic*
  • Gene Expression Regulation, Neoplastic*
  • HEK293 Cells
  • Humans
  • In Situ Hybridization, Fluorescence / methods
  • Neoplasms / genetics*
  • Promoter Regions, Genetic
  • RNA Splicing
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Single-Cell Analysis
  • Telomerase / genetics*
  • Telomerase / metabolism
  • Telomere / metabolism


  • RNA, Messenger
  • TERT protein, human
  • Telomerase