CAN AN OLD BIRD BE TAUGHT NEW TRICKS? TELOMERE LENGTH INCREASES WITH AGE IN A LONG-LIVED BIRD.
M.F. Haussmann, D.W. Winkler, K.M. O'Reilly, C.E. Huntington, C.M. Vleck
Department of Zoology and Genetics,
Iowa State University,
Ames, IA 50011
Cell survival is dependent on the presence of telomeric DNA at the ends of linear chromosomes. Telomeres function in stabilizing chromosomal end integrity, inhibiting aberrant fusions and rearrangements that occur on broken chromosomes and aiding in the completion of duplication. Cellular aging is normally accompanied by telomere shortening and this has been shown in a variety of tissues. Telomeres shorten with age in a number of species including rodents, humans and chickens, but telomeres can be elongated de novo by the activity of the enzyme telomerase. In the present study, we investigated telomere length in a variety of bird species to determine whether telomeres shorten with age and at what rate. Blood samples were taken from known age Zebra finches (Taeniopygia guttata), Tree swallows (Tachycineta bicolor), Adelie penguins (Pygoscelis adeliae) and Leach's storm-petrels (Ocenaodroma leucorhoa) for telomere length analysis. Briefly, DNA was extracted from erythrocytes using a salt extraction, alcohol precipitation method and was than digested with restriction enzymes and separated on a non-denaturing agarose gel. Gels were hybridized with 32P-labeled (C3TA2)4 oligonucleotides. Densitometry was used to determine telomere lengths. Mean telomere lengths decreased as age increased in Zebra finches (F1,23 = 29.89, P < 0.0001, r2 = 0.54), Tree swallows (F1,47 = 23.27, P < 0.0001, r2 = 0.34) and Adelie penguins (F1,21 = 18.54, P < 0.0003, r2 = 0.47). There was an approximate reduction in telomere length of 515 ± 94 (SE) bp per year in Zebra finches, 295 ± 65 (SE) bp per year in Tree swallows, and 233 ± 54 (SE) bp per year in Adelie penguins. Surprisingly, telomeres do not shorten with age in Leach's storm-petrels but in contrast appear to lengthen (F1,31 = 59.69, P < 0.0001, r2 = 0.66) at a rate of 75 ± 10 (SE) bp per year. These results are particularly interesting because when body size is controlled for, Leach's storm-petrels are a long-lived bird that can live up to thirty years of age, while Zebra finches, Tree swallows and Adelie penguins are relatively short-lived. Telomeres shorten with age in essentially all other organisms that have been examined, and these contrasting results in a long-lived bird are surprising. Birds in general live substantially longer than similarly sized mammals and are known to possess superior defenses to reduce oxidative damage. If these long-lived birds have evolved other age-combating adaptations such as active telomere elongation by telomerase, freeing them from the constraint on cellular life span normally imposed by shortening telomeres, then they may prove to be an excellent model for aging studies.
Key words:
aging, telomere, bird, telomerase
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