ATRX is a chromatin remodelling factor found at a wide range of tandemly repeated sequences including telomeres (TTAGGG)n. ATRX mutations are found in nearly all tumours that maintain their telomeres ...via the alternative lengthening of telomere (ALT) pathway, and ATRX is known to suppress this pathway. Here, we show that recruitment of ATRX to telomeric repeats depends on repeat number, orientation and, critically, on repeat transcription. Importantly, the transcribed telomeric repeats form RNA–DNA hybrids (R‐loops) whose abundance correlates with the recruitment of ATRX. Here, we show loss of ATRX is also associated with increased R‐loop formation. Our data suggest that the presence of ATRX at telomeres may have a central role in suppressing deleterious DNA secondary structures that form at transcribed telomeric repeats, and this may account for the increased DNA damage, stalling of replication and homology‐directed repair previously observed upon loss of ATRX function.
Synopsis
This study shows that ATRX recruitment to G‐rich tandem repeats depends on repeat transcription, length and orientation and is associated with R‐loops. ATRX loss increases R‐loops at these sites suggesting that ATRX resolves DNA secondary structures.
Recruitment of ATRX at G‐rich tandem repeats depends on transcription and is associated with the presence of R‐loops.
ATRX recruitment depends on the non‐template strand being G‐rich suggesting the presence of G quadruplex DNA.
R‐loops at these sites increase in the absence of ATRX.
This study shows that ATRX recruitment to G‐rich tandem repeats depends on repeat transcription, length and orientation and is associated with R‐loops. ATRX loss increases R‐loops at these sites suggesting that ATRX resolves DNA secondary structures.
N
-Methyladenosine (m
A) on mRNAs mediates different biological processes and its dysregulation contributes to tumorigenesis. How m
A dictates its diverse molecular and cellular effects in leukemias ...remains unknown. We found that YTHDC1 is the essential m
A reader in myeloid leukemia from a genome-wide CRISPR screen and that m
A is required for YTHDC1 to undergo liquid-liquid phase separation and form nuclear YTHDC1-m
A condensates (nYACs). The number of nYACs increases in acute myeloid leukemia (AML) cells compared with normal hematopoietic stem and progenitor cells. AML cells require the nYACs to maintain cell survival and the undifferentiated state that is critical for leukemia maintenance. Furthermore, nYACs enable YTHDC1 to protect m
A-mRNAs from the PAXT complex and exosome-associated RNA degradation. Collectively, m
A is required for the formation of a nuclear body mediated by phase separation that maintains mRNA stability and control cancer cell survival and differentiation.
N6-Methyladenosine (m6A) on mRNAs mediates different biological processes and its dysregulation contributes to tumorigenesis. How m6A dictates its diverse molecular and cellular effects in leukemias ...remains unknown. We found that YTHDC1 is the essential m6A reader in myeloid leukemia from a genome-wide CRISPR screen and that m6A is required for YTHDC1 to undergo liquid-liquid phase separation and form nuclear YTHDC1-m6A condensates (nYACs). The number of nYACs increases in acute myeloid leukemia (AML) cells compared with normal hematopoietic stem and progenitor cells. AML cells require the nYACs to maintain cell survival and the undifferentiated state that is critical for leukemia maintenance. Furthermore, nYACs enable YTHDC1 to protect m6A-mRNAs from the PAXT complex and exosome-associated RNA degradation. Collectively, m6A is required for the formation of a nuclear body mediated by phase separation that maintains mRNA stability and control cancer cell survival and differentiation.
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•YTHDC1 is required for AML cell survival, differentiation state, and leukemogenesis•YTHDC1 binds to m6A and forms nuclear condensates (nYACs) mediated by LLPS•nYACs are more abundant in AML cells compared with normal blood cells•nYACs protect mRNAs (i.e., MYC and others) from degradation by the PAXT complex
Using AML cell lines and patient samples Cheng et al. identify a requirement for YTHDC1 in myeloid leukemogenesis. YTHDC1 undergoes liquid-liquid phase separation by binding to m6A to form dynamic nuclear condensates. These nuclear bodies are increased in myeloid leukemia cells and protect mRNAs from the PAXT-exosome complex.
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