Nucleic Acids Research Advance Access published online on October 23, 2009
Nucleic Acids Research, doi:10.1093/nar/gkp877
Gene Regulation, Chromatin and Epigenetics |
Drosophila mini-white model system: new insights into positive position effects and the role of transcriptional terminators and gypsy insulator in transgene shielding
1Department of the Control of Genetic Processes and 2Department of Drosophila Molecular Genetics, Institute of Gene Biology, Russian Academy of Sciences, 34/5 Vavilov Street, Moscow, 119334, Russia
*To whom correspondence should be addressed. Tel: +7 499 1359734; Fax: +7 499 1354105; Email: georgiev_p{at}mail.ru
Correspondence may also be addressed to Oksana Maksimenko. Tel: +7 499 1359906; Fax: +7 499 1354105; Email: mog{at}genebiology.ru
Received September 7, 2009. Revised September 30, 2009. Accepted October 2, 2009.
The white gene, which is responsible for eye pigmentation, is widely used to study position effects in Drosophila. As a result of insertion of P-element vectors containing mini-white without enhancers into random chromosomal sites, flies with different eye color phenotypes appear, which is usually explained by the influence of positive/negative regulatory elements located around the insertion site. We found that, in more than 70% of cases when mini-white expression was subject to positive position effects, deletion of the white promoter had no effect on eye pigmentation; in these cases, the transposon was inserted into the transcribed regions of genes. Therefore, transcription through the mini-white gene could be responsible for high levels of its expression in most of chromosomal sites. Consistently with this conclusion, transcriptional terminators proved to be efficient in protecting mini-white expression from positive position effects. On the other hand, the best characterized Drosophila gypsy insulator was poorly effective in terminating transcription and, as a consequence, only partially protected mini-white expression from these effects. Thus, to ensure maximum protection of a transgene from position effects, a perfect boundary/insulator element should combine three activities: to block enhancers, to provide a barrier between active and repressed chromatin, and to terminate transcription.