R-loop homeostasis at transposable elements safeguards transcriptional silencing in replication-quiescent oocytes

Area of Science:

• Molecular Biology
• Genetics
• Reproductive Biology

Background:

• R-loops (RNA:DNA hybrids) are implicated in genome stability but their transcriptional roles are unclear, especially in replicating cells.
• Replication processes confound the study of R-loops in proliferating cells, necessitating replication-free systems.

Purpose of the Study:

• To investigate the dynamic transcriptional roles of R-loops in replication-free oocytes.
• To characterize the location-dependent regulatory functions of R-loops at gene promoters and transposable elements.
• To elucidate the role of R-loops in female germ cell development and fertility.

Main Methods:

• Utilized replication-free oocytes to avoid confounding replication processes.
• Employed RTACC-seq, a high-specificity R-loop mapping technique for low-input samples.
• Investigated the effects of Rnaseh1 deletion on R-loops, chromatin, and transcriptional silencing in oocytes.

Main Results:

• Identified dynamic R-loop enrichment at gene promoters and transposable elements in oocytes.
• Observed R-loop accumulation at transposable elements in active oocytes, resolving with transcriptional silencing.
• Demonstrated opposing regulatory functions: reduced transcription at promoters and enhanced transcription at transposable elements.
• Showed that Rnaseh1 deletion leads to persistent R-loops, impaired silencing, and subfertility.

Conclusions:

• R-loops play dynamic, location-dependent roles in transcriptional regulation and chromatin remodeling.
• R-loops are crucial mediators of transcriptional silencing and chromatin condensation during oocyte maturation.
• R-loops are essential for maintaining female germ cell developmental competence and fertility.