First impressions can be misleading. The enzyme telomerase has been well studied because of its initial association with cell ageing processes and cancer — but it now seems that this is not all it can do. The way in which a biological entity is firstidentified can limit perceptions of the full range of its functions. The telomerase enzyme, for instance, was originally discovered on the basis of its vital ability to lengthen telomer es — the stretches of non-coding DNA at the ends of chromosomes. If it is too short, a telomere loses the ability to maintain a protective str uc-ture at the end of the chromosome, and such shortened telomeres can signal to cells to cease multiplying, in a process called cellular senescence. In this issue, Sarin et al.(page 1048) report provocative evidence that telomerase does more than merely synthesize DNA at chromosome ends: a key subunit of the enzyme stimulates the proliferation of mouse hair-follicle stem cells, generating shaggy mice. Strikingly, this occursindependently of the DNA-synthesis capacity of telomer ase.
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