One paper One week: When RNA self-regulates

This blog is based on the paper titled “Mutual feedback regulation between Poly(A)-specific” (Kyritsis et al., 2026); however, this paper did not have a graphical abstract that summarizes the findings, so I used a graphical abstract from another paper by Shukla et al. (2019) that summarizes "the gist" of the paper: PARN regulates miRNA stability but it is itself regulated by specific miRNAs.

PARN-mediated miRNA stability through deadenylation of poly (A) tail. Schematic showing how PARN regulates miRNA homeostasis. In normal cells, PAPD5-mediated adenylation marks select miRNAs for degradation, while PARN removes these tails, protecting miRNAs from decay by exonucleases such as DIS3L and DIS3L2. In PARN-deficient conditions, this balance is disrupted, leading to increased miRNA degradation and downstream effects on pathways like p53 (transcription factor involved in stress signalling). Figure is from Shukla et al., 2019, Molecular Cell.

This framework complements the findings discussed this week, where PARN not only regulates miRNA maturation (e.g., miR-29a, miR-1207) but is itself regulated by these miRNAs, forming a feedback loop that extends this model from linear control to dynamic, bidirectional regulation.

Adapted from Shukla et al., 2019, Molecular Cell.

ribonuclease (PARN) and cognate microRNAs

We often learn about gene regulation as part of the central dogma of the cell: DNA → RNA → protein.

This paper challenges that simplicity.

It shows that RNA doesn’t only carry information; it is self-regulating through dynamic, feedback interactions.

Meet the system: PARN and microRNAs

At the center of this study is PARN, a deadenylase enzyme that shortens a stretch of adenine nucleotides, or poly(A) tails (Zhang et al., 2015), and microRNAs (miRNAs), short RNAs that tune gene expression by silencing target transcripts.

Individually, both are well studied. But together, they form something intriguing.

Not a pathway: a loop

The core discovery is a bidirectional regulatory relationship.

PARN binds to specific primary microRNAs, particularly miR-29a, and alters their poly(A) tail length. This directly impacts their stability and maturation (Dehlin et al., 2000), placing PARN at an early step in microRNA biogenesis.

But the regulation doesn’t stop there.

Those same microRNAs (miR-29a and miR-1207) target PARN mRNA, reducing its expression.

There’s a feedback loop:

• PARN regulates microRNA maturation

• microRNAs regulate PARN levels

And this loop is coordinated, in part, by CPSF6, which appears to recruit PARN to newly formed RNA transcripts.

Small changes, real consequences

The changes in microRNA levels are modest. This is expected.

MicroRNAs don’t act like switches; they act like dimmers, fine-tuning gene expression across networks. Subtle shifts can have meaningful biological effects.

From molecules to movement

The study connects this molecular loop to a clear cellular outcome: cell migration.

When PARN levels are reduced, microRNA levels rise, and cells become more mobile. When PARN is overexpressed, migration decreases.

This balance between PARN and microRNAs directly influences cell motility, a process central to cancer progression and metastasis.

The bigger picture

This work reframes how we think about regulation.

It’s not linear, but interconnected, dynamic, and self-regulating.

PARN emerges not just as an RNA-processing enzyme, but as a guardian of microRNA biogenesis, acting across multiple stages from early transcript processing to final maturation and turnover. More broadly, this study reminds us:

Biology isn’t built on straight lines, but on feedback and balance.

References: 

Dehlin, E., M. Wormington, C.G. Körner and E. Wahle. 2000. Cap-dependent

deadenylation of mRNA. The EMBO Journal. 19:1079-1086.

Kyritsis, A., R.A. Beta, D. Scutelnic, V. Stravokefalou, V. Del Vescovo, Z.V. Arsenopoulou, K. Papikinos, M. Grasso, F. Fontana, P. Moutopoulou, A. Tsiporis, M. Samiotaki, G. Panayotou, M.A. Denti, and N.A. Balatsos. 2026. Mutual feedback regulation between Poly(A)-specific ribonuclease (PARN) and cognate microRNAs. Life Sci Alliance. 9.

Shukla, S., G.A. Bjerke, D. Muhlrad, R. Yi, and R. Parker. 2019. The RNase PARN Controls the Levels of Specific miRNAs that Contribute to p53 Regulation. Mol. Cell. 73:1204-1216 e1204.

Zhang, X., E. Devany, M.R. Murphy, G. Glazman, M. Persaud, and F.E. Kleiman. 2015. PARN deadenylase is involved in miRNA-dependent degradation of TP53 mRNA in mammalian cells. Nucleic Acids Res. 43:10925-10938.