Regulation and effects of modulation of telomerase reverse transcriptase expression in primordial germ cells during development.

Telomere length maintenance in the germ line from generation to generation is essential for the perpetuation of eukaryotic organisms. This task is performed by a specialized reverse transcriptase called telomerase. While this critical function of telomerase has been well established, the mechanisms that regulate telomerase in the germ line are still poorly understood. We now show, using a Pou5f1-GFP transgenic mouse model, that telomerase suppression in quiescent male primordial germ cells (PGCs) is accompanied by a decrease in expression of murine telomerase reverse transcriptase (TERT). To further assess the role of TERT in quiescent PGCs, we developed a chicken Actb gene promoter/cytomegalovirus enhancer (CAG)-Tert transgenic mouse strain that constitutively expresses murine TERT. Telomerase activity was detected in quiescent PGCs from CAG-Tert transgenic embryos, demonstrating that re-activation of TERT expression is sufficient to restore telomerase activity in these cells and implying that TERT expression is an important mechanism of telomerase regulation in PGCs. Fluorescence-activated cell-sorting (FACS) analysis of PGC frequency and cell cycle status revealed no effect of either overexpression or deficiency of TERT in CAG-Tert transgenic mice or Tert knock-out mice respectively. These results demonstrate that TERT per se does not affect proliferation or development of PGCs, in contrast with recent studies that suggest that TERT has a telomere-independent effect in certain stem cells. It is possible that the direct effect of TERT on cell behavior may be dependent on cell type.