Telomeres are nucleoprotein complexes that protect the ends of eukaryotic linear chromosomes from degradation and fusion. Telomere dysfunction leads to developmental disorders, oncogenesis and aging. A telomere consists of DNA repeats and their bound proteins, as well as a telomeric RNA that is transcribed from telomeric repeats. Transcription of telomeric repeats is a conserved feature of telomeres in all studied species. Telomeric transcripts are maintained at a low level but their significant fraction is retained near telomeres. The telomeres of Drosophila are maintained in the absence of telomerase, by the transpositions of the specialized telomeric non-LTR retrotransposons; the HeT-A element being the most abundant. Here, we address a question on the factors of telomere instability in the Drosophila female germline. The level of HeT-A RNA in the germline is regulated by Piwi-interacting (pi) RNAs, the nuclear RNA surveillance system and transcription factors. Depletions of any of these components leading to the upregulation of HeT-A expression cause early embryonic lethality. It is suggested that accumulation of chromatin-bound telomeric RNA can destabilize telomeric DNA, leading to DNA lesions and recombination events. To find out more about a link between telomeric RNA abundance and telomere instability, we performed a study of the telomere integrity when the telomeric RNA biogenesis was impaired, which led to HeT-A overexpression. Moreover, abundant telomeric transcripts were revealed in a specific RNA fraction associated with chromatin. We detected the presence of H2Av, the main marker of DNA breaks, on telomeres after HeT-A derepressing, suggesting that HeT-A overexpression could cause DNA breaks in telomeres. Moreover, the presence of DNA breaks in telomeres was accompanied by the appearance of R-loops, the DNA-RNA hybrid structures associated with DNA damage. Chromatin immunoprecipitation was done to prove the accumulation of R-loops in telomeres. The formation of R-loops is most likely caused by retention of HeT-A transcripts in chromatin. Thus, telomere-associated RNA is an essential factor of telomere stability during normal oogenesis and early development. Funding: Program for Molecular and Cellular Biology of Presidium of Russian Academy of Sciences