包含端粒重复的RNA（TERRA）从亚端粒区域转录到端粒。TERRA RNA可以侵入端粒的双链DNA并形成端粒R-环结构。越来越多的证据表明，TERRA介导的R-环在端粒长度稳态中扮演着重要角色。在这里，我们将回顾有关在端粒水平调节R-环水平的当前知识。特别是，我们将讨论中心玩家TERRA及其结合蛋白通过各种机制调节R-环水平的方式。我们还将提供TERRA介导的持久或非定期R-环在人类ALT癌症和其他生物体中的端粒中的后果概述，重点关注重复干扰引起的损伤和DNA同源重组介导的修复后端粒长度调节。

Telomeric repeat containing RNA (TERRA) is transcribed from subtelomeric regions to telomeres. TERRA RNA can invade telomeric dsDNA and form telomeric R-loop structures. A growing body of evidence suggests that TERRA-mediated R-loops are critical players in telomere length homeostasis. Here, we will review current knowledge on the regulation of R-loop levels at telomeres. In particular, we will discuss how the central player TERRA and its binding proteins modulate R-loop levels through various mechanisms. We will further provide an overview of the consequences of TERRA-mediated persistent or unscheduled R-loops at telomeres in human ALT cancers and other organisms, with a focus on telomere length regulation after replication interference-induced damage and DNA homologous recombination-mediated repair.