The research team, led by Shuo Yang, Yongjing Li, Deqi Sun, Chenyu Shi, Qi Li and Shikai Liu of the Ocean University of China in Qingdao, tackled a question that has long frustrated biologists working on indirectly developing animals. Many marine invertebrates pass through a larval stage that looks and behaves nothing like the adult, and metamorphosis demands that the nervous system be substantially reworked to serve a completely different lifestyle. In the Pacific oyster, Magallana gigas, the larva swims and senses its surroundings using structures such as the apical organ, but once it cements itself to a surface, those larval systems are largely discarded and adult ganglia take over. How the adult nervous system is organized, and whether its different ganglia have specialized roles, had remained unresolved at the cellular level.

Single-nucleus RNA sequencing offered a way in. Rather than profiling whole tissues, which averages signals across many cell types, the technique captures the transcriptome of individual nuclei, allowing researchers to identify and classify every major cell type present. The team applied this approach to the adult cerebral ganglia, known as CG, and the visceral ganglion, or VG, generating cell-type atlases that distinguish neurons, glial cells and other supporting populations. Comparative analysis of the two atlases revealed clear ganglion-associated differences in cellular composition and in the transcriptional programs running inside the neurons themselves, suggesting that the two structures do genuinely different jobs for the animal.

Those differences showed up most clearly in pathway-level analyses. Using differential expression testing, enrichment of KEGG pathway annotations, and a single-cell method called AUCell that estimates gene set activity in each individual cell, the researchers found that neurons of the cerebral ganglia were transcriptionally biased toward homeostatic and protective processes. In practical terms, the CG neurons expressed gene programs associated with maintaining internal stability and defending the animal against stress. The visceral ganglion told a different story. Its neurons showed higher activity in pathways linked to signal modulation and effector output, consistent with a role in regulating the muscular and physiological actions of an animal that must pump water, filter food and manage its internal organs while anchored in place.

Importantly, these functional biases were not simply a by-product of having different mixtures of cell types in the two ganglia. The team compared transcriptionally matched neuronal populations, meaning neuron groups in the CG and VG that are molecularly similar to one another, and found that the pathway differences persisted even then. The biases were also accompanied by distinct patterns of transcription factor expression, the master regulatory genes that shape a cell’s identity and behavior. This indicates that the two ganglia are governed by different regulatory logic at a fundamental level, not just different sums of their parts.

One of the study’s most striking findings concerned serotonin, the neurotransmitter better known by its chemical name 5-hydroxytryptamine, or 5-HT. Serotonergic neurons, those that produce and use serotonin as their signaling molecule, were primarily identified in the visceral ganglion. No corresponding population could be resolved in the cerebral ganglia. To understand how this serotonergic program is controlled, the researchers deployed a suite of computational tools. Virtual knockout experiments, which simulate the loss of specific regulatory genes, together with gene regulatory network inference using the GENIE3 algorithm and pseudotime analysis, which orders cells along a developmental trajectory, converged on a candidate Gata3–Pitx–Uncx regulatory module associated with the 5-HT program. In other words, three families of transcription factors appear to work in concert to define and maintain the oyster’s serotonergic neurons.

The atlases also illuminated the often-overlooked supporting cast of the nervous system. Among the non-neuronal cells, the team identified a population they describe as metabolic glial cells, which displayed gene expression features related to transport, redox balance, detoxification and amino acid metabolism. To test whether these cells truly resemble glia, the researchers combined cell–cell communication analysis, pseudotime modeling, and a cross-species cell-type similarity approach called SAMap, which aligns single-cell datasets from different organisms. All three lines of evidence supported a glial-like identity for these cells and suggested that they may perform neural-support functions analogous to those of glial cells in better-studied animals, providing metabolic and protective services to the surrounding neurons.

Placed alongside earlier work on the larval apical organ, the new findings allow the authors to propose a working model of neural adaptation across the oyster’s life cycle. In the larva, the apical organ serves as the dominant sensory and integrative hub. After metamorphosis, the model suggests, functional emphasis may shift toward the adult visceral ganglion, which takes on responsibilities suited to the sessile adult, from coordinating effector outputs to housing the serotonergic signaling system. The cerebral ganglia, meanwhile, lean toward homeostatic upkeep. This is framed as a testable framework rather than a settled conclusion, and the authors point the way toward future experimental validation, for example by functionally perturbing the candidate regulatory module or the serotonergic neurons to see how oyster behavior and physiology respond.

Beyond molluscan biology, the study has broader resonance. Single-cell and single-nucleus atlases have transformed vertebrate neuroscience, but invertebrate nervous systems, particularly those of animals that undergo radical metamorphosis, remain largely unmapped. The oyster, as an economically critical aquaculture species and an ecologically important reef builder, offers a system in which neural adaptation can be studied against a well-defined life-history transition. Understanding how its ganglia specialize could inform breeding and hatchery practices, since larval settlement and post-metamorphic survival are major bottlenecks in oyster aquaculture, and both depend on a nervous system that has successfully navigated its remodeling.

The work also adds to a growing appreciation that nervous system evolution and development operate with remarkable flexibility. A regulatory module involving Gata3, Pitx and Uncx family factors steering a serotonin program, and glial-like cells devoted to metabolism and detoxification, suggest that the molecular grammar of neural support and modulation is deeply conserved, even as the anatomical solutions differ wildly between a bivalve and a mammal. For now, the adult oyster’s brain, long treated as a diffuse and undifferentiated tangle, has revealed itself to be a compartmentalized, molecularly specialized organ, and its secrets are only beginning to come into focus.

Subject of Research: Single-nucleus transcriptomics of adult Pacific oyster cerebral and visceral ganglia to characterize neural remodeling after metamorphosis.

Article Title: Single-nucleus transcriptomics reveals cellular signatures of adaptive remodeling in the adult oyster nervous system after the life-history transition

Article References: Yang, S., Li, Y., Sun, D., Shi, C., Li, Q., & Liu, S. (2026). Single-nucleus transcriptomics reveals cellular signatures of adaptive remodeling in the adult oyster nervous system after the life-history transition. BMC Biology. https://doi.org/10.1186/s12915-026-02743-z

Image Credits: AI Generated

DOI: 10.1186/s12915-026-02743-z

Keywords: Pacific oyster, Magallana gigas, single-nucleus RNA sequencing, metamorphosis, serotonergic neurons, visceral ganglion, cerebral ganglia, transcription factors, glial cells, neural adaptation, BMC Biology, gene regulatory network