EXPRESSION OF TELOMERASE ACTIVITY IN HUMAN CHORION

Telomerase activation is required for cellular immortalization and is found in most malignant tumors. Normal somatic cells are generally tel omerase negative, except for stem cells in renewing tissues. During pr egnancy, human trophoblast continues to proliferate and acts as prolif erating stem cells for the development of chorion and the formation of placenta. In the present study, a total of 105 chorions from placenta s at various weeks of gestation were examined for telomerase activity using the telomeric repeat amplification protocol (TRAP) assay. Twenty -five of 33 (76%) normal early chorions at 5 to 9 weeks gestation were telomerase-positive. Chorions from early spontaneous abortions also-e xhibited telomerase activity but at a low level. In contrast, only 2 ( 4%) late chorions at 34 to 41 weeks gestation expressed telomerase act ivity. Significant telomerase activity was observed in trophoblast cel l fractions of chorion, demonstrating trophoblast to be the source of the activity. Expression of human telomerase catalytic subunit (hTRT) was observed in early chorions, but not in late placenta, and there wa s a close correlation between telomerase activity and hTRT expression. In contrast, expression of human telomerase RNA component (hTR) was o bserved in both early and late chorions and was not Liked to telomeras e activity. These findings suggest that telomerase activity in chorion is critically regulated over the course of gestation associated with hTRT expression. The findings of the present study also appear to supp ort the emerging concept that normal somatic cells with stem cell-like characteristics can express telomerase activity. (C) 1997 Academic Pr ess.