Madalena Christiane Rodriguez Gutierrez, Andrioli Luiz Paulo Moura, Gorab Eduardo
Departamento de Genética e Biologia Evolutiva, Instituto de Biociências, Universidade de São Paulo, Rua do Matão 277, Cidade Universitária, São Paulo, SP, Brazil, CEP 05508-090.
Chromosome Res. 2008;16(8):1233-41. doi: 10.1007/s10577-008-1271-1. Epub 2008 Nov 30.
Ribosomal RNA genes of most insects are interrupted by R1/R2 retrotransposons. The occurrence of R2 retrotransposons in sciarid genomes was studied by PCR and Southern blot hybridization in three Rhynchosciara species and in Trichosia pubescens. Amplification products with the expected size for non-truncated R2 elements were only obtained in Rhynchosciara americana. The rDNA in this species is located in the proximal end of the X mitotic chromosome but in the salivary gland is associated with all four polytene chromosomes. Approximately 50% of the salivary gland rDNA of most R. americana larval groups analysed had an insertion in the R2 site, while no evidence for the presence of R1 elements was found. In-situ hybridization results showed that rDNA repeat units containing R2 take part in the structure of the extrachromosomal rDNA. Also, rDNA resistance to Bal 31 digestion could be interpreted as evidence for nonlinear rDNA as part of the rDNA in the salivary gland. Insertions in the rDNA of three other sciarid species were not detected by Southern blot and in-situ hybridization, suggesting that rDNA retrotransposons are significantly under-represented in their genomes in comparison with R. americana. R2 elements apparently restricted to R. americana correlate with an increased amount of repetitive DNA in its genome in contrast to other Rhynchosciara species. The results obtained in this work together with previous results suggest that evolutionary changes in the genus Rhynchosciara occurred by differential genomic occupation not only of satellite DNA but possibly also of rDNA retrotransposons.
大多数昆虫的核糖体RNA基因被R1/R2反转录转座子打断。通过PCR和Southern杂交技术，研究了R2反转录转座子在三种菌蚊属物种和柔毛毛蠓中的存在情况。仅在美洲菌蚊中获得了非截短R2元件预期大小的扩增产物。该物种的核糖体DNA位于有丝分裂X染色体的近端，但在唾液腺中与所有四条多线染色体相关。在分析的大多数美洲菌蚊幼虫群体中，约50%的唾液腺核糖体DNA在R2位点有插入，而未发现R1元件存在的证据。原位杂交结果表明，含有R2的核糖体DNA重复单元参与了染色体外核糖体DNA的结构。此外，核糖体DNA对Bal 31消化的抗性可解释为唾液腺中核糖体DNA存在非线性结构的证据。Southern杂交和原位杂交未检测到其他三种菌蚊物种核糖体DNA中的插入，这表明与美洲菌蚊相比，它们基因组中的核糖体DNA反转录转座子明显较少。与其他菌蚊属物种相比，显然仅存在于美洲菌蚊中的R2元件与其基因组中重复DNA含量的增加相关。这项工作获得的结果与先前的结果表明，菌蚊属的进化变化不仅通过卫星DNA，还可能通过核糖体DNA反转录转座子的不同基因组占据而发生。
