This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Viewed from above, Danionella cerebrum offers a rare sight in a vertebrate: its brain, visible through the top of its head. Since the species was adopted for neuroscience research in 2018 and formally described in 2021, the tiny, transparent fish has drawn rapidly growing interest for its unique biology.
Whitehead Institute researchers recognized another opportunity in the tiny fish: it brought whole-animal single-cell profiling within reach, allowing the team to create the first comprehensive map of cell types and gene activity across an adult vertebrate. That perspective could help reveal how cells in different tissues coordinate their responses—and how changes in one part of the body influence others. In a study published in Science, the team profiled more than 600,000 cells from across the fish to build the whole-body map of which genes are active in which cell, known as a single-cell transcriptome atlas.
A cell's transcriptome is the full set of RNA molecules it has made from its DNA at a given time, providing a snapshot of which genes the cell is using. Together, the data provide a molecular reference for the cell types found throughout Danionella, the patterns of gene activity that distinguish them, and where many of them are located. The atlas also gives researchers a baseline for exploring how injury, aging, drugs or other changes affect cells across the whole animal.
"Once you have a spatially resolved atlas, you know what cell types exist, but you also know the neighbors of those cell types in this context," says Kutay Deniz Atabay, who led the work as a postdoctoral researcher in the lab of Whitehead Institute member Peter Reddien. "This gives you access at multiple different levels of complexity, from molecular to cellular to systems." Cell atlases have become increasingly detailed, but extending them across a whole adult vertebrate has been difficult for a simple reason: size. Profiling the cellular diversity of larger animals comprehensively is technically demanding and expensive.
Danionella offered a unique way around that problem. Its miniature body—barely 1 centimeter (0.4 inches) long—makes the experiment possible, while its close relationship to zebrafish allows researchers to draw on genetic tools developed for one of biology's most widely used model organisms. Atabay first became interested in Danionella in early 2019, while searching for a small, transparent animal in which he could watch the nervous system regenerate.
Its miniature size and accessible brain made it especially promising for that work, and the researchers found that the fish has broad regenerative capacity, including in the brain and fins. Reddien's lab, meanwhile, had already seen the value of a comprehensive whole-animal cell atlas through its work on planarians, regenerative flatworms whose small size had made such an atlas possible. Together, those interests led to a larger question.
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