Mohan Kommu Naga, Rani B Sandya, Kulashreshta Pooja Swaroop, Kadandale Jayarama S
Centre for Human Genetics, Biotech Park, Next to Aravind Mills, Bangalore 560100, India.
Chromosoma. 2011 Apr;120(2):165-75. doi: 10.1007/s00412-010-0299-0. Epub 2010 Nov 19.
We confirmed the occurrence of the insect TTAGG telomeric repeats in the mealybug Planococcus lilacinus, a radiation-resistant coccid, by single primer polymerase chain reaction (PCR) and Southern hybridization. Analysis of Bal31 nuclease-digested DNA by Southern hybridization and chromosomes by FISH suggests that these repeats occur mainly at the ends of the chromosomes. However, sequence analysis of the PCR products of TTAGG-associated sequences from genomic DNA showed their interstitial occurrence and association with certain unrelated low-copy repeats. Because of their shorter length, the interstitial TTAGG sequences were detectable by primed in situ hybridizations but not by FISH. Analysis of chromosomes recovered after irradiation by fluorescent in situ hybridization suggested acquisition of TTAGG repeats at a majority of the healed ends. We also observed mild telomerase activity in unirradiated insects which was further enhanced after irradiation. Taken together, these results suggest that the mealybug has an efficient mechanism of formation of TTAGG repeats at radiation-induced chromosome ends and constitutively active telomerase may be a feature associated with rapid recovery of chromosome ends damaged by ionizing radiation.
我们通过单引物聚合酶链反应（PCR）和Southern杂交，证实了在抗辐射球蚧类昆虫淡紫粉蚧中存在昆虫特有的TTAGG端粒重复序列。通过Southern杂交分析Bal31核酸酶消化的DNA以及通过荧光原位杂交（FISH）分析染色体表明，这些重复序列主要出现在染色体末端。然而，对基因组DNA中与TTAGG相关序列的PCR产物进行序列分析发现，它们存在于染色体间质中，并与某些不相关的低拷贝重复序列相关联。由于其长度较短，间质TTAGG序列可通过引物原位杂交检测到，但不能通过FISH检测到。通过荧光原位杂交分析辐射后回收的染色体表明，在大多数愈合的染色体末端获得了TTAGG重复序列。我们还在未受辐射的昆虫中观察到了微弱的端粒酶活性，辐射后该活性进一步增强。综上所述，这些结果表明，粉蚧在辐射诱导的染色体末端具有形成TTAGG重复序列的有效机制，组成型活性端粒酶可能是与电离辐射损伤的染色体末端快速恢复相关的一个特征。
