Developmental control of t-loops and end-protection

Chromosome-end protection is crucial for the maintenance of genome stability. Telomeres end with a 3’ single-stranded DNA overhang potentially bound by telomerase for elongation. This overhang is also able to tuck back into the duplex telomeric DNA to form the telomere-loop (t-loop) structure. T-loops are thought to protect chromosome-ends; however, this could not be formally demonstrated. Here, we identify TElomere Loop Stabilizing protein 1 (TELS1), a telomere-specific protein necessary for t-loop stabilization in pluripotent cells and upon pluripotency exit. We show that TELS1 dependent t-loops control telomerase recruitment but do not seem to be involved in telomere protection. I will present data suggesting that the t-loop is a biologically relevant structure, whose biogenesis and functions are developmentally regulated.