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Poly(A)-specific ribonuclease (PARN) mediates 3' end maturation of the telomerase RNA component

ABSTRACT: Mutations in the poly(A) ribonuclease (PARN) gene cause telomere diseases including familial idiopathic pulmonary fibrosis (IPF) and dyskeratosis congenita (DC)1,2, but how PARN deficiency impacts telomere maintenance is unclear. Here, using somatic cells and induced pluripotent stem (iPS) cells from DC patients with PARN mutations, we show that PARN is required for the 3′ end maturation of the telomerase RNA component (TERC). Patient cells as well as immortalized cells in which PARN is disrupted show decreased levels of TERC. Deep sequencing of TERC RNA 3′ termini reveals that PARN is required for removal of posttranscriptionally acquired oligo(A) tails that target nuclear RNAs for degradation. Diminished TERC levels and the increased oligo(A) forms of TERC are normalized by restoring PARN, which is limiting for TERC maturation in cells. Our results reveal a novel role for PARN in the biogenesis of TERC, and provide a mechanism linking PARN mutations to telomere diseases.

ORGANISM(S): Homo sapiens

PROVIDER: GSE71709 | GEO | 2015/09/08

SECONDARY ACCESSION(S): PRJNA291863

REPOSITORIES: GEO

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Project description:Mutations in genes encoding components of the telomerase holoenzyme complex result in a spectrum of rare genetic disorders known as telomere diseases, including dyskeratosis congenita (DC). A consistent finding in DC due to pathogenic mutations in DKC1, which encodes dyskerin, is decreased steady-state levels of the non-coding RNA component of telomerase (TERC) and thus impaired telomere maintenance. Dyskerin binds hundreds of other small nucleolar RNAs (snoRNAs). However, the mechanisms by which DKC1 mutations cause variable impacts on these snoRNAs are poorly understood, which is a barrier to understanding disease mechanisms in DC beyond impaired telomere maintenance. Here, using somatic and induced pluripotent stem cells (iPSCs) from DC patients with DKC1 mutations and CRISPR-Cas9-engineered iPSCs, we show that mutations in the N-terminal extension domain (NTE) of dyskerin dysregulate the biogenesis of a subset of snoRNAs, with the most prominent effect on scaRNA13 (small Cajal body-specific RNA 13). In patient iPSCs carrying the del37L dyskerin NTE-domain mutation but not in those with C-terminal mutations, nascent scaRNA13 transcripts showed a discrete population of 3´-extended forms, as seen in the setting of DC-causing mutations in the PARN (polyA-specific ribonuclease) gene. By deep sequencing of RNA 3´ ends, we found that aberrant scaRNA13 transcripts were composed of genomically-encoded extensions and post-transcriptionally oligoadenylated species, mediated by the noncanonical polymerase PAPD5, which counters PARN. NTE domain mutations generated using CRISPR-Cas9 engineering of the endogenous DKC1 recapitulated the scaRNA13 3´-end processing defects seen in del37L patient cells. Conversely, repair of the DKC1 del37L mutation and genetic or pharmacological manipulation of PAPD5 rescued scaRNA13 end processing defects and steady-state levels. Analysis of the human telomerase cryo-EM structure showed that the dyskerin NTE interacts with 3´ end of bound RNA, suggesting that mutations in this domain impair 3´ end protection of nascent scaRNA13 in addition to canonical functions in snoRNA stabilization. Our results provide mechanistic insights into the interplay of dyskerin and the PARN/PAPD5 axis in the biogenesis and accumulation of snoRNAs beyond TERC, which has important implications for our broader understanding of ncRNA dysregulation in human diseases.

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Poly(A)-specific ribonuclease (PARN) mediates 3' end maturation of the telomerase RNA component

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