5/ Mapping all 4 components on a single radial axis (r=1 , shell midpoint) shows that ssC-rich and ssG-rich repeats occupy distinct compartments in an APB: the ssC-rich repeats overlapped with the PML shell, TRF1-marked telomeres occupy the interior, and ssG-rich repeats spread broadly throughout.
4/ The ssC-rich repeats were enriched within the PML shell, while ssG-rich repeats were abundant in the APB interior. The ssG-rich signal comprised mostly DNA as it was RNase-resistant and proximal to POT1 (peak distance ~17 nm).
3/ The images revealed that PML in an APB is not a filled droplet. It rather assembles into a partially open ~70 nm-thick spherical shell with an uneven protein distribution and a lower density than canonical PML bodies. This shell is the scaffold and coordinate system for everything inside.
2/ 3D MINFLUX nanoscopy with multiplexed exchange DNA-PAINT conducted at the @bioquant.bsky.social imaging platform (tinyurl.com/2auwmbfu) localized individual PML and TRF1 proteins together with ssG-rich and ssC-rich telomere repeats at ~3 nm precision.
6/ This strand-segregated topology constrains the ALT mechanism. The t-loop resolution at the PML shell could generate a C-circle template, driving rolling-circle amplification into G-rich repeats inside. Mechanistic ALT models can now be tested against the actual APB structure. Read the preprint!
1/ Some cancers can proliferate without telomerase. They recombine and extend their telomeres inside ALT-associated PML bodies (APBs). @emmakoeleman.bsky.social @dkfz.bsky.social mapped where proteins and single-stranded telomeric repeats sit in APBs: doi.org/10.64898/202... 🧵
