A new imaging breakthrough captures the nanoscale choreography of nuclear import and export in living cells

In the complex symphony of cellular life, one of the most elegant and essential performances takes place at the boundary between the nucleus and the cytoplasm. It’s a molecular ballet involving thousands of proteins, RNAs, and molecular complexes moving in and out of the nucleus every second. Until recently, this process was largely hidden behind a veil of spatial and temporal limitations. Now, thanks to the power of live-cell super-resolution microscopy, we’re finally watching it unfold in exquisite detail.

In a landmark study published in Nature (2025), Sau et al. employed 3D MINFLUX nanoscopy, a cutting-edge super-resolution technique, to track how individual molecules navigate the nuclear pore complex (NPC)—the cell’s tightly regulated gateway between the nucleus and cytoplasm. What they uncovered challenges long-standing models of nuclear transport and reveals new insights into the inner architecture and dynamics of this essential structure.

Why nuclear transport matters

Every eukaryotic cell contains a nucleus, where DNA is housed and transcribed into RNA. To carry out its function, the cell must continuously shuttle proteins, RNAs, and ribonucleoproteins across the nuclear envelope via nuclear pore complexes. These NPCs are massive molecular machines made up of about 1,000 protein components, forming a permeability barrier that allows only selected cargoes to pass through—either passively (for small molecules) or actively (for larger macromolecular complexes).

Understanding how this selective transport works is critical. Disruptions to NPC function have been linked to a wide range of diseases, from cancer and neurodegeneration to viral infections. Yet, due to their tiny size and rapid dynamics, observing the precise mechanics of nuclear transport in live cells has remained a formidable challenge.

Enter super-resolution microscopy: A revolution in 3D molecular tracking

Conventional microscopy lacks the spatial and temporal resolution to observe molecular events at the scale and speed required to resolve NPC dynamics. Enter MINFLUX (Minimal Photon Fluxes), a technique that merges the principles of STED and single-molecule localization microscopy (SMLM) to achieve nanometre-scale spatial resolution and sub-millisecond temporal resolution.

What sets MINFLUX apart is its ability to localize single fluorophores using minimal light exposure, significantly reducing photobleaching and allowing longer observation of dynamic processes in living cells.

In this study, the researchers implemented two-colour 3D MINFLUX, simultaneously labelling the NPC scaffold and the protein importin α (Imp α)—a shuttle protein responsible for ferrying cargo into the nucleus. With one colour fixed on the NPC and another tracking Imp α, the team was able to reconstruct molecular trajectories through the pore in real time, in three dimensions.

Surprising discoveries inside the nuclear pore

What they saw upended traditional expectations.

1. Overlapping import and export routes
   Contrary to the assumption that import and export pathways must be spatially separated to avoid molecular “traffic jams,” the study found that both occur within overlapping regions near the periphery of the pore—within a 46 nm-wide annulus—but not through the central core.

2. A vacant core
   Surprisingly, the central axis of the NPC—once assumed to be the main channel—was completely devoid of traffic. This “vacant centre” is now thought to be inaccessible for cargo, possibly due to structural constraints or the presence of a molecular plug.

3. Three distinct transport zones
   The researchers propose a new model in which the NPC is divided into three concentric zones:

   • A central exclusion zone that remains traffic-free

   • An active transport zone where cargoes are translocated

   • A peripheral arrest zone where molecules occasionally pause, perhaps for processing or regulation.

4. Slow and constrained dynamics
   Molecules moved through the NPC at diffusion rates up to 1,000 times slower than in free solution—highlighting the complex, regulated nature of transport within this nanostructure. Motion was punctuated by pauses, suggesting transient binding events or structural constraints.

Beyond the gateway: broader implications

The findings go beyond improving our understanding of the NPC. They open new possibilities for studying passive diffusion, nucleocytoplasmic transport regulation, and drug targeting at unprecedented precision. The methods established here could also be extended to other dynamic nanoscale processes in live cells.

Moreover, the study highlights the importance of developing high-fidelity imaging techniques that don’t distort biological behaviour. Earlier methods often relied on high-intensity illumination that may have altered transport dynamics through photodamage or selection bias. MINFLUX, with its low photon budget and long observation time, preserves biological authenticity—making it a gold standard for live-cell nanoscopy.

A new era of molecular microscopy

This work by Sau and colleagues sets a powerful precedent. By merging nanometre precision with live-cell compatibility, Super-resolution microscopy turns the invisible into the observable, the fleeting into the measurable. It transforms our understanding of the nuclear pore from a static gate into a dynamic, highly organized, and surprisingly elegant system.

As super-resolution imaging continues to evolve, the frontier of cellular biology is shifting from what we can guess to what we can see, track, and quantify. In the not-so-distant future, we may be watching other molecular “dances” across membranes, within organelles, or between signalling proteins—live, in colour, and in 3D.

Further Reading:
📄 Sau et al. “Overlapping nuclear import and export paths unveiled by two-colour MINFLUX”. Nature (2025). DOI link

Keywords: nuclear pore complex, super-resolution microscopy, MINFLUX, importin, nuclear transport, live-cell imaging, nanoscale dynamics, nucleocytoplasmic transport