Preferential maintenance of critically short telomeres in mammalian cells heterozygous for mTert

doi:10.1073/pnas.062549199

Preferential maintenance of critically short telomeres in mammalian cells heterozygous for mTert

^*Ontario Cancer Institute/Amgen Research Institute, Department of Medical Biophysics, University of Toronto, 620 University Avenue, Toronto, ON, Canada M5G 2C1; and ^‡Amgen, Inc., One Amgen Center Drive, Thousand Oaks, CA 91320

Edited by Mary-Lou Pardue, Massachusetts Institute of Technology, Cambridge, MA, and approved January 22, 2002 (received for review October 15, 2001)

Abstract

Prolonged growth of murine embryonic stem (ES) cells lacking the telomerase reverse transcriptase, mTert, results in a loss of telomere DNA and an increased incidence of end-to-end fusions and aneuploidy. Furthermore, loss of only one copy of mTert also results in telomere shortening intermediate between wild-type (wt) and mTert-null ES cells [Liu, Y., Snow, B. E., Hande, M. P., Yeung, D., Erdmann, N. J., Wakeham, A., Itie, A., Siderovski, D. P., Lansdorp, P. M., Robinson, M. O. & Harrington, L. (2000) Curr. Biol. 10, 1459–1462]. Unexpectedly, although average telomere length in mTert ^+/− ES cells declined to a similar level as mTert-null ES cells, mTert ^+/− ES cell lines retained a minimal telomeric DNA signal at all chromosome ends. Consequently, no end-to-end fusions and genome instability were observed in the latest passages of mTert ^+/− ES cell lines. These data uncover a functional distinction between the dosage-dependent function of telomerase in average telomere-length maintenance and the selective maintenance of critically short telomeres in cells heterozygous for mTert. In normal and tumor cells, we suggest that telomerase activity insufficient to maintain a given average telomere length may, nonetheless, provide a protective advantage from end-to-end fusion and genome instability.

Footnotes

↵ † Present address: Oak Ridge National Laboratory, Building 1061, MS-6445, Oak Ridge, TN 37831.
↵ § To whom reprint requests should be addressed. E-mail: leah{at}uhnres.utoronto.ca.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

TERT,

telomerase reverse transcriptase;

ES,

embryonic stem cells;

TRAP,

telomere repeat amplification protocol;

TR,

telomerase RNA;

Flow-FISH,

flow cytometry fluorescence in situ hybridization;

Q-FISH,

quantitative FISH;

wt,

wild type;

p,

passage