Insights into the evolution of mammalian telomerase: platypus TERT shares similarities with genes of birds and other reptiles and localizes on sex chromosomes.
BACKGROUND
The TERT gene encodes the catalytic subunit of the telomerase complex and is responsible for maintaining telomere length. Vertebrate telomerase has been studied in eutherian mammals, fish, and the chicken, but less attention has been paid to other vertebrates. The platypus occupies an important evolutionary position, providing unique insight into the evolution of mammalian genes. We report the cloning of a platypus TERT (OanTERT) ortholog, and provide a comparison with genes of other vertebrates.


RESULTS
The OanTERT encodes a protein with a high sequence similarity to marsupial TERT and avian TERT. Like the TERT of sauropsids and marsupials, as well as that of sharks and echinoderms, OanTERT contains extended variable linkers in the N-terminal region suggesting that they were present already in basal vertebrates and lost independently in ray-finned fish and eutherian mammals. Several alternatively spliced OanTERT variants structurally similar to avian TERT variants were identified. Telomerase activity is expressed in all platypus tissues like that of cold-blooded animals and murine rodents. OanTERT was localized on pseudoautosomal regions of sex chromosomes X3/Y2, expanding the homology between human chromosome 5 and platypus sex chromosomes. Synteny analysis suggests that TERT co-localized with sex-linked genes in the last common mammalian ancestor. Interestingly, female platypuses express higher levels of telomerase in heart and liver tissues than do males.


CONCLUSIONS
OanTERT shares many features with TERT of the reptilian outgroup, suggesting that OanTERT represents the ancestral mammalian TERT. Features specific to TERT of eutherian mammals have, therefore, evolved more recently after the divergence of monotremes.
Section of Molecular Genetics and Microbiology, School of Biological Science, University of Texas at Austin, 78712-1095, USA.
Radmila
R
Hrdličková
Jiří
J
Nehyba
Shu Ly
SL
Lim
Frank
F
Grützner
Henry R
HR
Bose
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001717:Birds / Q000235:genetics*; D003001:Cloning, Molecular; D019143:Evolution, Molecular; D005260:Female; D008297:Male; D008394:Marsupialia / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D010987:Platypus / Q000235:genetics*; D012104:Reptiles / Q000235:genetics*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012730:Sex Chromosomes; D012754:Sharks / Q000235:genetics; D026801:Synteny; D019098:Telomerase / Q000235:genetics*; D059505:Telomere Homeostasis
D019098:Telomerase