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Title: DIRS RETROELEMENTS IN ARTHROPODS: IDENTIFICATION OF THE RECENTLY ACTIVE TCDIRS1 ELEMENT IN THE RED FLOUR BEETLE, TRIBOLIUM CASTANEUM

Author
item GOODWIN, T - UNIV OTAGO, DUNEDIN, NZ
item POULTER, R - UNIV OTAGO, DENEDIN, NZ
item LORENZEN, MARCE - KANSAS STATE UNIV
item Beeman, Richard

Submitted to: Molecular and General Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2004
Publication Date: 11/15/2004
Citation: Goodwin, T.J., Poulter, R.T., Lorenzen, M.D., Beeman, R.W. 2004. DIRS retroelements in arthropods: identification of the recently active TcDirs1 element in the red flour beetle, Tribolium castaneum. Molecular and General Genomics 272: 47-56.

Interpretive Summary: Comparative study of animal genes can shed light on relatedness of insects to other animals and can give insight on insect-specific genetic targets for pest control. We found an unusual jumping gene in the flour beetle that has never before been found in insects or any other arthropods, but has been seen in slime molds and sea urchins. This research shows that some genes that are very specific for a few animals can occasionally invade unrelated species, and underscores the need to better understand mechanisms that either restrict or permit movement of genes between species. Only in this way can we have confidence that pest-specific approaches to insect control will retain their desired specificity.

Technical Abstract: The DIRS family of retrotransposons is an eclectic and widespread group of mobile genetic elements. Members of this group differ from most other known retrotransposons in that they encode a tyrosine recombinase (YR) and lack genes for DDE integrase and aspartic protease. The DIRS family of elements can be divided into two subgroups: the ITR elements, such as DIRS-1 itself from Dictyostelium discoideum, that have inverted terminal repeats (ITRs) and in which the entire reverse transcriptase/ribonuclease H (RT-RH) open reading frame (ORF) is overlapped by the 5' half of the YR ORF; and the SDR elements that have split direct repeats (SDRs) and lack long overlapping ORFs. This subdivision is also supported by phylogenetic analyses of RT-RH sequences. DIRS elements have been identified in slime mold, fungi, plants, and a range of animals including nematodes, echinoderms and vertebrates. Here we present an analysis of the first DIRS element identified in any arthropod. This element, TcDirs1, was found in the red flour beetle, Tribolium castaneum. It is generally similar in sequence and structure to DIRS-1 and bears the characteristic inverted terminal repeats of the ITR elements. Unlike other ITR elements, however, the YR ORF of TcDirs1 has only a short overlap of the RT-RH ORF, suggesting it has evolved an alternative strategy for expressing the YR. Elements similar in sequence and structure to TcDirs1 were also identified in two species of sea urchin, indicating that this alternative arrangement of coding regions is compatible with activity and has probably been in existence since early in metazoan evolution. TcDirs1 is widespread in T. castaneum and appears to have been recently mobile. Some copies may still be active and, given their presence in an experimentally tractable host, might serve as useful models for the study of DIRS-like retrotransposons.