DEVELOPMENTAL AND TISSUE-SPECIFIC REGULATION OF MOUSE TELOMERASE AND TELOMERE LENGTH

Telomere shortening and telomerase activation in human somatic cells h ave been implicated in cell immortalization and cellular senescence. T o further study the role of telomerase in immortalization, we assayed telomere length and telomerase activity in primary mouse fibroblasts, in spontaneously immortalized cell clones, and in mouse tissues. In th e primary cell cultures, telomere length de creased with increased cel l doublings and telomerase activity was not detected. In contrast, in spontaneously immortalized clones, telomeres were maintained at a stab le length and telomerase activity was present. To determine if telomer e shortening occurs in vivo, we assayed for telomerase and telomere le ngth in tissues from mice of different ages. Telomere length was simil ar among different tissues within a newborn mouse, whereas telomere le ngth differed between tissues in an adult mouse. These findings sugges t that there is tissue-specific regulation of mouse telomerase during development and aging in vivo. In contrast to human tissues, most mous e tissues had active telomerase. The presence of telomerase in these t issues may reflect the ease of immortalization of primary mouse cells relative to human cells in culture.