mTert expression correlates with telomerase activity during the differentiation of murine embryonic stem cells

Telomerase, the enzyme which maintains the ends of linear chromosomes in eu karyotic cells, is found at low levels in somatic stem cells but while this is incapable of preventing the progressive erosion of telomeres occurring as a consequence of cell division, such cells show greater proliferative ca pacity than normal somatic cells hence examination of telomerase activity i n such stem cells is of interest. Our aim in this work was to examine the r elationship between expression of the reverse transcriptase component (mTer t) of murine telomerase. We report here the insertion of a reporter cassett e comprising a segment of the promoter sequence of murine Tert gene coupled to the coding sequence of green fluorescent protein (GFP) into murine embr yonic stem (ES) cells and show that this is sufficient for mimicking the ex pression of mTert. We show that the expression of mTert is very closely lin ked to telomerase activity and that both are substantially reduced upon dif ferentiation of ES cells into more committed lineages giving us a potential reporter system for the selection and isolation of ES cells possessing dif ferent levels of telomerase activity. (C) 2000 Elsevier Science Ireland Ltd . All rights reserved.