Overview
On September 9, 2026, a team at HHMI's Janelia Research Campus published WHOLISTIC in *Nature*: an imaging system that simultaneously records the activity of nearly every cell in a living vertebrate — the zebrafish larva — at cellular resolution and second-scale temporal precision. For the first time, the conversations of cells across the cardiovascular, digestive, and nervous systems were captured at the same time, while the fish swam, fed, and slept.
Nearly all cells communicate using calcium ions: muscle contraction, synaptic firing, fertilization, and apoptosis all rely on them. By converting calcium concentration changes into visible light, researchers can watch cells "talking."
The Four Pillars of WHOLISTIC
1. Whole-body transgenesis — making nearly every cell in the fish express a calcium sensor; the prerequisite for the entire method. 2. High-speed volumetric imaging — no single microscope configuration fits all tissues, since different cell types have different signal characteristics and dynamic ranges. 3. Computational alignment and cell-type identification — many cell types show unique temporal activity patterns, enabling cell identification by behavior alone, even without specific labels. 4. Whole-body expansion microscopy — physically enlarging tissue to reveal fine structures, used to cross-validate the identities of cells captured in the recordings.
Work was done in zebrafish larvae, with proof of concept in adult *Danionella cerebrum*. Collaborators include University College London, Virginia Tech, and Tsinghua University.
Key Findings
- Cellular scale: Cartilage cells (chondrocytes) respond to cold — counterintuitive, since they are not traditionally listed as cold-sensing cells. Meninges respond to ketamine, meaning the drug activates not only neurons but also connective tissue around the brain and spinal cord.
- Organ scale: Rhythmic traveling waves along nephrons.
- Multi-organ scale: Previously unknown muscle synergies and muscle–organ interactions.
- Whole-body scale: During hypoxia, the brainstem drives a whole-body redistribution of blood flow from the gut to the brain and muscles — a coordinated survival response previously only inferable indirectly.
- Sleep lead: During prolonged locomotor rest, activity waves propagate along the spinal cord and brain, originating from ependymal cells lining the fluid-filled cavities of the central nervous system. This is a lead, not a conclusion; its connection to sleep requires dedicated experiments.
- Sensor coverage: dozens of tissue types with very different cell biology, unlike the brain's more uniform promoter strategies.
- Volumetric imaging speed: calcium signals are sub-second; fast signals, large volumes, and limited phototoxicity are in tension.
- Data volume: whole-body time-series data far exceed whole-brain data, requiring redesigned alignment, denoising, and segmentation.
- Identity confirmation: expansion microscopy provides the structural verification step.
Why It Took a Decade
Whole-brain calcium imaging existed ten years ago; pushing to the whole body required solving four engineering problems:
Limitations
The method only works in naturally transparent animals. Zebrafish larvae are transparent for only a few days; *Danionella* stays transparent for life but is tiny with a limited behavioral repertoire. Mammals are out of reach — scattering is a physical limit, not an engineering one. WHOLISTIC remains far from imaging an entire human body.
Next Steps
The team is adapting the method to adult *Danionella cerebrum*, which offers lifelong transparency and more complex adult behaviors. Combined with optogenetics, WHOLISTIC enables all-optical causal dissection: activate a specific cell group with light while reading out whole-body responses — moving from correlation to causation.
Near-term applications include:
1. Whole-body drug side effects — current screening focuses on target organs, missing off-target tissue responses. 2. Sleep and resting-state mechanisms — if the ependymal cell lead holds. 3. Intercellular organ compensation — e.g., hypoxia-driven blood redistribution, familiar in critical care but previously only inferred.
Perspective
Misha Ahrens compared it to understanding a company by watching only one department: key insights live in the information flow between departments. Evolution, he notes, cares only that the organism works — not whether a decision happens in the prefrontal cortex or in a brainstem–bladder connection. Virginie Ruetten described the work as bridging two fundamental scales of biology — cell and organism — filling an "observability gap."
Verdict: WHOLISTIC's methodological significance currently outweighs its discoveries. The new observations across four scales are real and interesting but each needs follow-up mechanistic work. Its true contribution: making simultaneous study of physiology, neuroscience, behavior, and cell biology in a single animal routine.
References
1. phys.org, "A 'wholistic' view of cellular communication across an entire animal," 2026-09 — https://phys.org/news/2026-09-wholistic-view-cellular-communication-entire.html 2. *Nature* paper: Ruetten, Ahrens et al., WHOLISTIC whole-body in vivo imaging system, published online 2026-09-09 3. Times of India coverage, 2026-09