Sasaki T, Fujiwara H
Graduate School of Frontier Sciences, University of Tokyo, Japan.
Eur J Biochem. 2000 May;267(10):3025-31. doi: 10.1046/j.1432-1033.2000.01323.x.
Telomeres of most insects consist of pentanucleotide (TTAGG)n repeats, although the repeats are absent in Diptera and some other insect species, where the telomere regions are perhaps maintained without telomerase. To understand various and unusual telomere formation in insects, we have studied the characteristic features of a putative insect telomerase that has not been previously described. Using a modified telomeric repeat amplification protocol (TRAP), we first detected the telomerase activity in crickets, cockroaches and two Lepidopteran insects. The telomerase from crickets and cockroaches required dATP, dGTP and dTTP but not dCTP as a substrate and sequence analyses of the products of TRAP revealed that the (TTAGG)n repeats are synthesized by telomerase. The cockroach telomerase was detected both in somatic (fat body, muscle and neural tissues) and germ line (testis) cells, suggesting that expression of this enzyme is not regulated in a tissue-specific manner at an adult stage. While we detected high levels of telomerase activity in crickets and cockroaches, we could not detect activity in all tissues and cell cultures of the silkworm, Bombyx mori and in two Drosophila and one Sarcophaga cell lines. This supports the theory that Dipteran insects maintain their telomeres without telomerase.
大多数昆虫的端粒由五核苷酸（TTAGG）n重复序列组成，不过双翅目昆虫和其他一些昆虫物种中不存在这种重复序列，在这些物种中，端粒区域可能在没有端粒酶的情况下得以维持。为了了解昆虫中各种不同寻常的端粒形成方式，我们研究了一种此前未被描述过的假定昆虫端粒酶的特征。我们使用改良的端粒重复序列扩增协议（TRAP），首先在蟋蟀、蟑螂和两种鳞翅目昆虫中检测到了端粒酶活性。蟋蟀和蟑螂的端粒酶需要dATP、dGTP和dTTP作为底物，但不需要dCTP，并且对TRAP产物的序列分析表明，（TTAGG）n重复序列是由端粒酶合成的。在蟑螂的体细胞（脂肪体、肌肉和神经组织）和生殖细胞（睾丸）中都检测到了端粒酶，这表明在成虫阶段，这种酶的表达不受组织特异性方式的调控。虽然我们在蟋蟀和蟑螂中检测到了高水平的端粒酶活性，但在家蚕、两种果蝇以及一种麻蝇细胞系的所有组织和细胞培养物中都未检测到活性。这支持了双翅目昆虫在没有端粒酶的情况下维持其端粒的理论。
