Identification and characterization of the telomerase reverse transcriptase of Bombyx mori (silkworm) and Tribolium castaneum (flour beetle)

Chromosomal ends of most eukaryotes are composed of simple telomeric repeats. Arthropod telomeres are generally constituted by TTAGG pentanucleotide repeats; however, some insect species including Drosophila melanogaster do not have telomeric repeats. In contrast, the domestic silkworm Bombyx mori contains TTAGG-type telomeric repeats, but the telomerase activity has not been detected in all investigated tissues. To search for a cause of unusual telomere structure in insects, we here identified telomerase reverse transcriptase (TERT) subunit from the domestic silkworm B. mori and the flour beetle Tribolium castaneum. This is the first report of telomerase genes from arthropods. The domestic silkworm TERT gene (BmoTERT) and the flour beetle TERT gene (TcasTERT) both did not have the N-terminal GQ motif. Comparison between cDNA and genomic DNA of BmoTERT revealed that it includes no introns. BmoTERT contains five ATG codons in its 5'UTR, which could reduce the translation of BmoTERT proteins. Also, Northern hybridization indicated that BmoTERT is transcribed at a very low level. These unique features of BmoTERT possibly explain the undetectable Bombyx telomerase activity.