Control of telomere elongation and telomeric silencing in Drosophila melanogaster.
Chromosome length in Drosophila is maintained by the targeted transposition of two families of non-LTR retrotransposons, HeT-A and TART. Although the rate of transposition to telomeres is sufficient to counterbalance loss from the chromosome ends due to incomplete DNA replication, transposition as a mechanism for elongating chromosome ends raises the possibility of damaged or deleted telomeres, because of its stochastic nature. Recent evidence suggests that HeT-A transposition is controlled at the levels of transcription and reverse transcription. HeT-A transcription is found primarily in mitotically active cells, and transcription of a w+ reporter gene inserted into the 2L telomere increases when the homologous telomere is partially or completely deleted. The terminal HeT-A array may be important as a positive regulator of this activity in cis, and the subterminal satellite appears to be an important negative regulator in cis. A third chromosome modifier has been identified that increases the level of reverse transcriptase activity on a HeT-A RNA template and greatly increases the transposition of HeT-A. Thus, the host appears to play a role in transposition of these elements. Taken together, these results suggest that control of HeT-A transposition is more complex than previously thought.
Mason
J M
JM
Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709-2233, USA. masonj@niehs.nih.gov
Haoudi
A
A
Konev
A Y
AY
Kurenova
E
E
Walter
M F
MF
Biessmann
H
H
D000818:Animals; D005786:Gene Expression Regulation / Q000235:genetics; D020868:Gene Silencing; D006570:Heterochromatin / Q000235:genetics; D016615:Telomere
D006570:Heterochromatin