Telomere dynamics in cells with introduced telomerase: a rapid assay for telomerase activity on telomeres

Most immortal cell lines derived from human cancers or transformed in vitro maintain telomeres by endogenous expression of telomerase. In the present work, immortal cells that already express endogenous telomerase activity were induced to overexpress an exogenous telomerase (hTERT) and were analyzed for changes in telomere length. Introduction of hTERT into telomerase-positive immortal cell lines results in elevated telomerase activity as measured by the TRAP assay, leading to elongated telomeres in the cell lines tested. We explore possibilities for regulatory differences among the cell lines, including the level of overexpression of the catalytic subunit hTERT and the endogenous levels of telomere binding proteins. Reducing levels of hTERT expression with a construct containing an inefficient translation initiation sequence provided sufficient telomerase expression for maximal rates of telomere elongation. Overexpression of the hTERT alters the telomere length normally maintained in these cells and provides a very useful assay for the rapid analysis of telomerase activity on its native substrate, telomeres.

Two inactive fragments of the integral RNA cooperate to assemble active telomerase with the human protein catalytic subunit (hTERT) in vitro

We have mapped the 5' and 3' boundaries of the region of the human telomerase RNA (hTR) that is required to produce activity with the human protein catalytic subunit (hTERT) by using in vitro assembly systems derived from rabbit reticulocyte lysates and human cell extracts. The region spanning nucleotides +33 to +325 of the 451-base hTR is the minimal sequence required to produce levels of telomerase activity that are comparable with that made with full-length hTR. Our results suggest that the sequence approximately 270 bases downstream of the template is required for efficient assembly of active telomerase in vitro; this sequence encompasses a substantially larger portion of the 3' end of hTR than previously thought necessary. In addition, we identified two fragments of hTR (nucleotides +33 to +147 and +164 to +325) that cannot produce telomerase activity when combined separately with hTERT but can function together to assemble active telomerase. These results suggest that the minimal sequence of hTR can be divided into two sections, both of which are required for de novo assembly of active telomerase in vitro.

[Risk of injuries, symptoms of excessive strain and preventive possibilities in cross-country skiing. A comparison between classical technique and skating technique]

A standardised questionnaire was drawn up and submitted to 690 cross-country skiers active in popular (pastime) sports, competitive sports and high-performance sports, between 1990 and 1993, covering a total of 189 injuries and 1,281 cases of complaints caused by overstrain. Over and above this, muscular imbalance and postural characteristics (for example, signs of vestibular syndrome) were examined in 94 of these skiers. Three times as many skiers (69.3%) reported on complaints than skiers reporting on injuries (20.3%). Complaints concerned particularly the lower extremities (45.9%), whereas injuries were more frequent at the upper extremities (47.6%). Minor injuries predominated (77%) such as sprains and distortions (23.8%), contusions (25.9%), skin injuries (13.7%) and muscle injuries (13.7%) as well as mild complaints (45.1%) such as blisters at the hand and feet. High-performance sportsmen (14.4%) are significantly most frequently injured when employing the skating technique, whereas in competitive sports the "classical" technique results in a greater incidence of accidents (16.1%). Most accidents occur during downhill skiing, on rutty and icy tracks, collisions, due to inadequate technique, lack of balance and unskilled handling. Complaints are significantly reported by competitive (70.8%) and high-performance sports people (74.8%) for both techniques. Whereas complaints at the lower extremities occur more often during skating technique (56.8%) than during the classical technique (34.5%), complaints concerning the trunk are seen more often with the classical technique (29.7%) than with the skating technique (8.9%). Complaints are caused by icy, rutty tracks, inadequate equipment, deficient training, muscular imbalances and previous damage. A large number of pointers on how to avoid pitfalls when employing the skating and classical techniques can be obtained via analysis of the injuries and complaints.