Chromatin Structure in Drosophila Telomeres
Drosophila Chromosome Structure Group
Instead of the simple telomeric repeats found in other organisms, Drosophila uses non-LTR retrotransposons to elongate its chromosome ends. Instead of the simple telomeric repeats found in other organisms, Drosophila uses non-LTR retrotransposons (HeT-A, TART and TAHRE, as a group abbreviated HTT) to elongate its chromosome ends. Targeted transposition creates terminal tandem arrays of retrotransposons with the oligo(A) tails facing the chromosome. One of these retrotransposon families, HeT-A, makes up the majority of elements in the terminal arrays and lacks a gene for reverse transcriptase, but transposes under laboratory conditions. The group is investigating the regulation of transcription of these telomere specific transposons.
In addition to the terminal HTT array, telomeres also have subterminal repeats, termed telomere-associated sequence, TAS. While TAS repeats are found in all species examined, the sequence varies among species and even among chromosome ends within an individual. In Drosophila, TAS causes repression of neighboring reporter genes (Golubovsky et al. 2001), although expression of transgenes in the HTT arrays resembles that of the same reporter in euchromatic regions of the chromosomes (Biessmann et al. 2005). TAS also regulates HeT-A transcription (Capkova Frydrychova et al. 2007). Based on the presence of chromatin proteins, both the HTT and TAS arrays exhibit chromatin structures intermediate between euchromatin and heterochromatin, although HTT generally resembles the former and TAS the latter (Capkova Frydrychova et al. 2008).