Recordanelles record RNA and preserve a cell's molecular past

Recordanelles record RNA in a way that lets researchers look into a cell's recent molecular past. Scientists at ETH Zurich engineered a synthetic organelle that continuously captures messenger RNAs and protects them from their usual degradation. When the cell is analyzed later, the archive can reveal genes that were active hours or even days earlier.

Conventional transcriptomics usually provides a snapshot. Messenger RNAs appear and disappear as gene activity changes, so a transient response may be completely gone by the time a sample is collected.

The new system, described in Nature Biotechnology, is designed to turn part of that fleeting activity into a molecular record.

The researchers call it a recordanelle, short for RNA recording organelle.

An RNA archive attached to mitochondria

A recordanelle is built from a single engineered fusion protein with three functional components.

One anchors the construct to the outer mitochondrial membrane. A second drives the formation of a biomolecular condensate, creating a distinct intracellular compartment. The third binds RNA.

In the best-performing version, the RNA-binding component recognizes poly(A) tails, a feature shared by most messenger RNAs. This allows the system to sample many endogenous transcripts rather than requiring researchers to preselect a particular gene.

Once captured, RNAs are protected from rapid degradation. The recordanelle can later be enriched with the mitochondrial fraction and its stored RNA read by sequencing.

In HEK293T human cells, the strongest designs contained transcript species representing genes that accounted for up to 90% of the expressed transcriptome.

That number does not mean the organelle sequestered 90% of all RNA molecules in a cell. Instead, transcripts from up to 90% of expressed genes were represented among the RNAs enriched in the recorder.

Importantly, this broad sampling did not substantially alter the overall cellular transcriptome under the conditions tested.

The signal disappeared, but its molecular trace remained

The critical test was whether recordanelles could preserve a transcriptional event after the event itself had ended.

The researchers first used an engineered gene that could be transiently switched on with doxycycline. In ordinary cells, the induced RNA rapidly returned to baseline after the stimulus was removed. RNA captured by the recordanelle remained detectable later.

They then tested a more complex endogenous response: interferon-beta signaling.

Interferon activates a coordinated program of immune-response genes. Cells were exposed to interferon and then allowed to recover after the signal was removed. Two days later, the characteristic interferon-stimulated gene signature had disappeared from control cells.

In cells carrying the optimized recordanelle, the signature was still present in the molecular archive.

The same history could be reconstructed at single-cell resolution. Under conditions in which the cells were not passaged, interferon-associated transcriptional information remained detectable for at least five days.

That is the conceptual advance. Instead of asking only what a cell is expressing at the moment it is collected, researchers can potentially recover evidence of an earlier transient state.

A recorder is also a perturbation

The recordanelle is not a natural cellular organelle, and the experiment does not show that cells have acquired an autonomous form of biological memory. It is a genetically encoded research tool deliberately introduced into cultured cells.

The work was also performed in engineered human cell lines. Whether the same approach can operate effectively in complex tissues or intact organisms remains to be established.

There is a deeper issue with any molecular recording system: a device that observes a cell also changes it.

A recordanelle requires expression of a foreign fusion protein, occupies space around the mitochondrial membrane and physically captures part of the cellular RNA pool. The authors therefore tested whether the system disrupted cellular physiology.

Under the conditions examined, they found no substantial effects on cell viability, ATP production, mitochondrial membrane potential, global gene expression or the cellular proteome. But they explicitly note that more subtle perturbations may exist beyond the assays performed.

The record also has a finite lifetime. As cells proliferate, previously captured RNAs are diluted and replaced by newly sampled transcripts. The system therefore behaves less like permanent storage and more like a continuously updated molecular archive.

That still changes what transcriptomics can ask. A conventional experiment largely asks, "What is this cell doing now?" A recordanelle adds another possibility: "What happened to this cell earlier?"

If the technology can be adapted to more complex biological systems, cells could become not only objects of observation but also temporary repositories of their own transcriptional history.