Insulator and Ovo Proteins Determine the Frequency and Specificity of Insertion of the gypsy Retrotransposon in Drosophila melanogaster

Abstract

The gypsy retrovirus of Drosophila is quite unique among retroviruses in that it shows a strong preference for integration into specific sites in the genome. In particular, gypsy integrates with a frequency of .10% into the regulatory region of the ovo gene. We have used in vivo transgenic assays to dissect the role of Ovo proteins and the gypsy insulator during the process of gypsy site-specific integration. Here we show that DNA containing binding sites for the Ovo protein is required to promote site-specific gypsy integration into the regulatory region of the ovo gene. Using a synthetic sequence, we find that Ovo binding sites alone are also sufficient to promote gypsy site-specific integration into transgenes. These results indicate that Ovo proteins can determine the specificity of gypsy insertion. In addition, we find that interactions between a gypsy provirus and the gypsy preintegration complex may also participate in the process leading to the selection of gypsy integration sites. Finally, the results suggest that the relative orientation of two integrated gypsy sequences has an important role in the enhancer-blocking activity of the gypsy insulator.

Chromatin insulators specifically associate with different levels of higher-order chromatin organization in Drosophila

“…We have also used antibodies against histone H3 tri-methylated at lysine 27 (H3K27me3), a histone posttranslational modification linked to transcriptional repression (Cao et al 2002;Plath et al 2003;Sarma et al 2008), as well as antibodies against histone modifications H3 acetylated at lysine 9 (H3K9ac), H3 acetylated at lysine 14 (H3K14ac), and H3 tri-methylated at lysine 4 (H3K4me3), which are normally associated with transcriptional activation (Barski et al 2007;Jenuwein and Allis 2001;Ng et al 2003;Santos-Rosa et al 2002;Wang et al 2008). In addition, we have also used H3 mono-methylated at lysine 27 (H3K27me1), which was previously identified because of its association with heterochromatin but also with DAPI bands as well as with active transcription (Barski et al 2007;Labrador et al 2008).…”

Interaction between a pair of gypsy insulators or between heterologous gypsy and Wari insulators modulates Flp site-specific recombination in Drosophila melanogaster

“…For example, Labrador et al (2008) found that distal enhancers could bypass two these insulators only when they were inserted in opposite orientations. These authors supposed that some additional sequences in the gypsy retrotransposon (provirus) form a stem-loop structure allowing this bypass, which is only possible when the two gypsy copies are in the opposite (but not the same) orientations.…”

Mobile DNA elements in the generation of diversity and complexity in the brain

“…However, gypsy transposons — LTR retrotransposons that are active in D. melanogaster — often insert into the ovo locus. Endogenous gypsy mobilization can thus be visualized when an endogenous gypsy transposon inserts into engineered ovo sequences, which results in the activation of a GFP reporter 21,27 . This approach has revealed that somatic gypsy insertions occur in aged D. melanogaster neurons 21 .…”