Epigenetic regulation of TERRA transcription, R-loop formation, telomere integrity and metacyclogenesis by base J in Leishmania major.

The hyper-modified DNA base J helps control termination of Pol II transcription at polycistronic transcription units (PTUs) in T. brucei and L. major, allowing epigenetic control of gene expression. The Telomere Repeat-containing RNA (TERRA) is synthesized in T. brucei by Pol I readthrough transcription of a telomeric PTU. While little is understood regarding TERRA synthesis and function, the hyper-modified DNA base J is highly enriched at telomeres in L. major promastigotes. We now show that TERRA is synthesized by Pol II in L. major and loss of base J leads to increased TERRA from multiple telomeric ends, presumably via readthrough transcription from an adjacent PTU. Furthermore, Pol II readthrough defects and increased TERRA correlate with increased telomeric DNA damage, increased differentiation of promastigotes to the infectious metacyclic life stage and decreased cell viability. These results help explain the essential nature of base J in Leishmania and provide insight regarding epigenetic control of RNA expression, telomere stability and parasite development during the life cycle of L. major.