# Control of telomerase recruitment and end protection by independent shelterin components

## TL;DR

The study shows that two proteins, TPP1 and POT1, have separate roles in controlling telomere protection and telomerase recruitment in mouse embryonic stem cells.

## Contribution

The research reveals that telomerase recruitment and end protection are controlled by genetically and molecularly separable mechanisms.

## Key findings

- TPP1 is essential for telomerase recruitment through its interaction with TIN2, independently of POT1.
- POT1 is not required for telomerase activity but is crucial for telomere end protection, independently of TPP1.
- The findings challenge the traditional open-closed telomere model by showing distinct molecular mechanisms for recruitment and protection.

## Abstract

Telomeres are proposed to alternate between “closed” states, in which chromosome ends are protected from DNA damage signaling and inaccessible to telomerase, and “open” states, where they become accessible for telomerase mediated elongation but less protected. Whether these states reflect distinct molecular mechanisms or mutually exclusive structural conformations remains unclear. Here, we develop a single-cell assay to monitor telomerase activity in mouse embryonic stem cells. Using this approach, we demonstrate that the shelterin component TPP1 is essential for telomerase recruitment via its interaction with TIN2, independently of POT1. In contrast, POT1 is dispensable for telomerase function but required for telomere end protection, acting independently of TPP1. These findings challenge the classical open-closed telomere model and reveal that telomerase recruitment and end protection are mediated by genetically and molecularly separable mechanisms.

Telomeres need to open from a close state which protects the chromosome ends to allow extension by telomerase. Here the authors reveal distinct roles of TPP1 and POT1 in telomerase recruitment and telomere protection using siingle-cell telomerase activity assay.