KUNMING, June 24 (Xinhua) -- Chinese scientists have for the first time mapped the entire brain of the primitive, fish-like lamprey by constructing a spatial single-cell atlas, offering an unprecedented view into the deep evolutionary origins of the vertebrate brain.
The complete cell atlas, published as the cover story in the journal Science, provides the most detailed look yet at the brain of an ancient lineage that diverged from the ancestors of all jawed vertebrates.
Lampreys are among the few surviving jawless vertebrates and have retained their core morphological features for approximately 360 million years, with little change throughout the fossil record. This extraordinary evolutionary stasis makes them uniquely valuable as a living reference point for reconstructing the ancestral state of the vertebrate nervous system.
The study was led by researchers from the Kunming Institute of Zoology (KIZ) of the Chinese Academy of Sciences, in collaboration with BGI Research and Liaoning Normal University.
The team found that, by constructing a spatial single-cell atlas covering the lamprey's entire brain, its cellular architecture could be compared with that of mice and zebrafish, which belong to the jawed-vertebrate lineage.
Remarkably, despite the vast evolutionary gulf separating lampreys from mammals, the researchers found multiple brain regions in the lamprey display gene expression patterns and cell type compositions highly similar to those in mice.
The finding suggests the common ancestor of all vertebrates may have already possessed a brain with distinct regional specialization and complex molecular organization, long before jaws or paired appendages evolved, said Su Bing, corresponding author of the study at KIZ.
One of the most striking findings relates to the functional nature of the lamprey's neurons. The team identified a population of neurons that exhibit both excitatory and inhibitory properties -- a "dual-function" or "part-time" characteristic. While such neurons remain relatively abundant in lampreys and zebrafish, they are largely replaced by specialized, single-function "full-time" neurons in mammals.
This shift from generalist to specialist neurons may represent a fundamental trend in brain evolution, enabling greater computational power and behavioral complexity, Su said.
The study also sheds fresh light on a long-debated question in evolutionary biology concerning the origin of the cerebellum, the brain structure essential for motor coordination and learning. In a region of the lamprey brain previously described as a "cerebellum-like area," the researchers identified cells that share striking molecular similarities with cerebellar interneurons found in zebrafish.
"This provides new molecular evidence that a primitive form of the cerebellum already existed in the earliest vertebrates, shedding fresh light on its long-debated origins," Su noted.
According to Su, the brain map is more than just a single-species dataset -- it serves as a "cross-era reference" that can guide future research into how complex brain structures emerge and diversify over evolutionary time. ■
