Characterizing somatic variation in normal human astrocytes with artificially induced telomere dysfunction
Telomerase is an enzyme expressed in germline cells that lengthens telomeres, the repetitive sequences at chromosome ends which naturally shorten with each replication. hTERT, the catalytic unit of telomerase, is reactivated in over 80% of human cancers. However, both length and structure are important for telomeres’ protective end-capping function. A protein complex called shelterin, which binds to telomeric repeats, is responsible for maintaining protective paperclip-like loops at chromosome ends. One vital protein in the shelterin complex is TRF2, which contains a telomeric dsDNA-binding Myb domain. An artificial allele called TRF2ΔBΔM, with the Myb domain removed, has been shown to disrupt shelterin in a dominant negative fashion and induce end-to-end chromosome fusions. While chromosome fusions and resultant bridge-fusion-break (BFB) cycles are a common mechanism of genomic instability in cancer, few have made efforts to sequence their products and understand how this telomere dysfunction contributes to human cancer. We are utilizing Normal Human Astrocytes (NHA) as a model in order to characterize the genomic products of artificially induced telomere dysfunction. NHA primary cells were transduced with hTERT for immortalization and later with TRF2ΔBΔM to induce telomere dysfunction and fusions. After the whole-genome sequencing of eight samples, our results suggest significantly increased structural breakends in hTERT TRF2ΔBΔM compared to hTERT and NHA primary cell lines. However, no copy number variation was detected. Future analysis of our dataset will focus on characterizing this somatic variation further. In future experiments, we hope to use an inducible TRF2ΔBΔM or long-read sequencing to better understand the relationship between telomere dysfunction and gliomagenesis.
