Cloning and sequencing of the breakpoint regions of inversion 5g fixed in Drosophila buzzatii
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Chromosomal inversions are ubiquitous in Drosophila both as intraspecific polymorphisms and interspecific differences. Many gaps still remain in our understanding of the mechanisms that generate them. Previous work has shown that in Drosophila buzzatii, three polymorphic inversions were generated by ectopic recombination between copies of the transposon Galileo. In this study, we have characterized the breakpoint regions of inversion 5g, fixed in D. buzzatii and absent in Drosophila koepferae and other closely related species. A novel approach comprising four experimental steps was used. First, D. buzzatii BAC clones encompassing the breakpoints were identified and their ends sequenced. Then, breakpoint regions were mapped at high resolution in the Drosophila mojavensis genome sequence. Finally, breakpoint regions were isolated by polymerase chain reaction in D. buzzatii and D. koepferae and sequenced. Our aim was to shed light on the mechanism that generated inversion 5g and specifically to test for an implication of the transposon Galileo. No evidence implicates Galileo or other transposable elements in the origin of inversion 5g that was generated most likely by two independent breaks and non-homologous end-joining repair. Our results show that different inversion-generating mechanisms may coexist within the same lineage and suggest a hypothesis for the evolutionary time and mode of their operation.
KeywordstRNA Gene Breakpoint Region Distal Breakpoint Ectopic Recombination Inversion Breakpoint
We thank Oriol Calvete, Alejandra Delprat, Barbara Negre and Marta Puig for technical support and comments on a previous version of the manuscript. Dmitri Petrov lent us generously his lab to carry out the final part of this project. Work supported by a PIF fellowship from the UAB awarded to O. P. da Costa and grant BFU2005-02237 from the Dirección General de Investigación (Ministerio de Educación y Ciencia, Spain) awarded to A. Ruiz.
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