TELOMERASE ACTIVITY DURING CARDIAC DEVELOPMENT

Telomerase is a ribonucleoprotein involved in maintaining telomere len gth in stem cells and immortal and actively dividing cells. We report here for the first time that telomerase is developmentally regulated i n the normal rat heart. When we compared rat hearts at different devel opmental stages, we found that telomerase activity decreased to 20% of the fetal level by 5 days after birth, and was undetectable by 20 day s after birth. These results indicate that the rate of cardiomyocyte p roliferation decreases dramatically soon after birth in the rat. Of se veral non-cardiac tissues examined, telomerase activity was highest in fetal and adult rat liner, suggesting that there is an active mechani sm for maintaining long telomeres in liver tissue at all stages. The d isappearance of telomerase activity in the rat heart at the time that cardiomyocytes become terminally differentiated suggests that telomera se downregulation is important in the permanent withdrawal of cardiomy ocytes from the cell cycle. (C) 1997 Academic Press Limited.