Ricerc@Sapienza

The maintenance of chromosome ends in Drosophila is an exceptional phenomenon
because it relies on the transposition of specialized retrotransposons rather than on the activity of
the enzyme telomerase that maintains telomeres in almost every other eukaryotic species.
Sequential transpositions of Het-A, TART, and TAHRE (HTT) onto chromosome ends produce
long head-to-tail arrays that are reminiscent to the long arrays of short repeats produced by
telomerase in other organisms. Coordinating the activation and silencing of the HTT array with the
recruitment of telomere capping proteins favors proper telomere function. However, how this
coordination is achieved is not well understood. Like other Drosophila retrotransposons, telomeric
elements are regulated by the piRNA pathway. Remarkably, HTT arrays are both source of piRNA
and targets of gene silencing thus making the regulation of Drosophila telomeric transposons a
unique event among eukaryotes. Herein we will review the genetic and molecular mechanisms
underlying the regulation of HTT transcription and transposition and will discuss the possibility of a
crosstalk between piRNA mediated regulation, telomeric chromatin establishment and telomere
protection.