The organism at the heart of this discovery is Stentor coeruleus, a unicellular protozoan recognized for its distinctive trumpet shape and remarkable size that renders it visible to the naked eye. Although lacking neurons, Stentor displays behavioral adaptations previously thought exclusive to multicellular animals with nervous systems. Specifically, these organisms demonstrate habituation, a fundamental form of learning characterized by diminished responses to repetitive, non-threatening stimuli. Understanding how Stentor achieves this at the cellular and molecular level holds profound implications for our grasp of the evolutionary origins of learning.

In the study published in Current Biology, UCSF researchers employed state-of-the-art neuroscience methodologies to monitor the habituation responses of Stentor when subjected to mechanical stimuli. Using a custom-built apparatus, the Stentors were mechanically jostled at one-minute intervals within petri dishes. Initial responses were conspicuous contractions and tail retractions, defensive measures triggered by disturbance. Fascinatingly, after repeated jolts, the organism’s reactions waned significantly, indicating a form of memory formation that allows it to distinguish relevant stimuli from innocuous perturbations.

Traditional models of memory formation in neurons implicate the synthesis of new proteins following a learning event, supported by genomic transcription and subsequent translation. To probe whether Stentor’s learning adhered to similar processes, the researchers deployed pharmacological agents that inhibited protein synthesis. Contrary to expectations, Stentor’s acquisition and retention of habituation accelerated under these conditions, suggesting a distinct mechanism divergent from that of complex animal neurons. This finding disrupts the classical view that long-term memory inevitably requires new protein production.

Delving deeper, the UCSF team embarked on quantifying gene expression profiles and protein abundance during different stages of habituation. Their experiments revealed that rather than relying on de novo protein synthesis, Stentor modified existing proteins through post-translational modifications. Central to this mechanism was the influx of calcium ions upon mechanical stimulation, activating calcium/calmodulin-dependent protein kinase II (CaMKII). CaMKII catalyzes the addition of chemical tags—phosphorylations—to target proteins, thereby altering their function and effectively encoding a molecular memory.

With each successive jolt, the chemical modification of proteins mediated by CaMKII fine-tuned the organism’s sensitivity to the mechanical stimuli. This gave rise to a cellular state less reactive to recurring disturbances, epitomizing habituation. Furthermore, the researchers observed that this biochemical memory was heritable; daughter cells retained the habituated state, implying the transmission of memory-associated molecular markers during cellular division. Such capability blurs the conventional demarcation between cognitive functions and unicellular life forms.

Fundamental to this molecular plasticity may be mechanoreceptors embedded in Stentor’s membrane, analogous to sensory receptors in animals. These mechanoreceptors likely serve as detection points for mechanical forces, initiating calcium signaling cascades that downstream modulate protein function via CaMKII-mediated phosphorylation. Animal neurons exploit a similar paradigm to adapt receptor responsiveness, reinforcing the idea that these learning-related molecular systems predate the evolution of complex nervous systems by considerable evolutionary time.

Wallace Marshall, PhD, the study’s senior author and a professor of Biochemistry and Biophysics at UCSF, remarked on the profound implications of the findings. According to him, the capacity for learning might be an inherent property entrenched at the cellular level, shared across the tree of life. “Stentors and humans might not seem alike at all,” he said, “but learning in both involves protein changes and calcium signaling, and it’s possible our brain cells may have borrowed this mechanism from earlier cells that could learn on their own.”

This research reframes the biological definition of learning and memory, illustrating that these phenomena are not confined to neurons or brains. Instead, they emerge from fundamental biochemical processes that regulate cellular behavior. The discovery prompts a re-examination of cognitive biology, suggesting that rudimentary forms of memory could be widespread among diverse unicellular life forms, shaping adaptability in fluctuating environments long before brains evolved.

By tracing the biochemical pathway of calcium influx and kinase activation in Stentor, the study paves new avenues for synthetic biology and bio-inspired computing. Harnessing such protein modification systems could inspire innovative approaches to engineering cellular memory or designing nanoscale devices capable of adaptive responses. The interdisciplinary implications cut across biochemistry, neurobiology, cell biology, and even applied sciences like nanotechnology.

In conclusion, the work by UCSF researchers not only uncovers how a brainless, single-celled organism learns but also expands our perspective on the molecular basis of cognition. It underscores the notion that the roots of learning are ancient, embedded within the basic molecular machinery present in the earliest life forms. As this domain unfolds, it may reshape fundamental biological paradigms, revealing that learning is a universal feature intricately woven into the fabric of life itself.

Subject of Research: Molecular mechanisms of learning in single-celled organisms
Article Title: How Brainless Single-Celled Organisms Learn Using Neuronal-Like Molecular Machinery
News Publication Date: April 22, 2024
Web References: Current Biology Publication
References: UCSF research publication in Current Biology (April 22, 2024)
Keywords: Stentor coeruleus, cellular neuroscience, habituation, calcium signaling, CaMKII, protein phosphorylation, molecular memory, unicellular learning, neurobiology, biochemistry, cell biology, receptor proteins

Protein lactylation, first characterized through histone modifications, constitutes the covalent attachment of lactate moieties to lysine residues on target proteins. This biochemical event extends beyond mere histone regulation, encompassing a variety of non-histone substrates and thereby broadening the scope of lactate’s influence within the cell. Unlike traditional epigenetic modifications such as acetylation and methylation, lactylation is intimately tied to metabolic flux, creating a molecular dialogue between metabolic activity and the control of gene transcription. This crosstalk underscores the sophistication with which cells integrate their metabolic environment with signaling pathways to direct fate decisions and functional outcomes.

The enzymology behind protein lactylation remains a critical focus area, with investigations identifying key enzymes responsible for installing and removing lactyl groups. Writers of this modification appear to utilize activated lactate derivatives, such as lactyl-CoA, as donors for the modification. Although the precise enzymatic players remain partially elusive, the paradigm suggests parallels with other acyltransferases, with a growing appreciation for the specialized machinery that couples metabolic products to epigenetic regulation. Meanwhile, dedicated "eraser" enzymes capable of removing lactyl marks are beginning to emerge, hinting at the dynamic and reversible nature of this modification that aligns it with classic epigenetic marks.

Functionally, histone lactylation has been implicated in the regulation of gene expression programs critical for cell differentiation, development, and responses to environmental challenges. For example, during macrophage activation, shifts in intracellular lactate levels modulate histone lactylation patterns, which in turn influence the transcriptional landscape governing inflammatory responses. This newly characterized dimension of metabolic-epigenetic interplay offers an explanation for how metabolic rewiring underlies cellular phenotypic plasticity and functional adaptation, effectively linking energy metabolism to immune function.

Beyond the nucleus, the identification of lactylation on non-histone proteins opens vast new frontiers for research. Lactylation can modulate the activity, localization, stability, and interaction networks of metabolic enzymes, signaling proteins, and transcription factors. These findings suggest a multifaceted regulatory framework where lactate signaling extends to numerous cellular compartments, shaping processes ranging from energy metabolism to signal transduction cascades. The breadth of this phenomenon implies that lactylation could serve as a universal mediator that fine-tunes cellular physiology in response to metabolic cues.

The pathophysiological implications of protein lactylation are profound. Elevated lactate levels and aberrant lactylation have been observed in diverse disease contexts, including cancer, cardiovascular disorders, and autoimmune diseases. Tumor cells, for instance, often exhibit heightened glycolysis and lactate production, which may fuel lactylation-dependent epigenetic reprogramming to promote malignancy, chemoresistance, and immune evasion. Understanding how lactylation pathways are hijacked in disease states presents opportunities to develop novel therapeutic interventions targeting these enzymatic processes or the downstream signaling effected by lactylated proteins.

In cardiovascular biology, accumulating data indicate that protein lactylation influences vascular remodeling, inflammation, and cardiac metabolism. The dynamic regulation of lactylation in response to ischemic stress and metabolic perturbations may underlie adaptive or maladaptive cardiac responses. Therapeutically modulating lactylation could therefore provide avenues to mitigate heart disease progression by restoring metabolic and gene expression homeostasis.

The developmental biology arena also stands to benefit from this burgeoning field, as evidence mounts for lactylation’s role in directing stem cell fate and tissue differentiation. Fluctuations in lactate levels during embryonic development may serve as metabolic signals that guide epigenetic modifications, thus shaping the complex choreography of gene expression necessary for proper organogenesis and morphogenesis.

Elucidating the crosstalk between lactylation and other post-translational modifications is an ongoing challenge. Proteins often undergo combinatorial modifications that collectively regulate their function, and understanding how lactylation fits into this regulatory code will be essential. Synergistic or antagonistic interactions with acetylation, methylation, phosphorylation, and ubiquitination may fine-tune cellular responses and contribute to the spatiotemporal precision of signaling networks.

Technological advances have been instrumental in unveiling the landscape of protein lactylation. Mass spectrometry-based proteomics, coupled with novel chemical probes and antibodies specific for lactylated residues, have enabled comprehensive identification and quantitation of lactylation sites. These tools continue to expand the catalog of lactylated proteins and provide mechanistic insights into their functional consequences across various biological systems.

The dynamics of lactate metabolism itself inform the regulation of lactylation. Cellular conditions that promote glycolytic flux, such as hypoxia or inflammatory stimuli, increase intracellular lactate pools, thereby enhancing the availability of lactyl donors. Conversely, metabolic reprogramming in response to nutrient deprivation or mitochondrial dysfunction can attenuate lactylation, linking environmental inputs with epigenomic landscapes. This metabolic sensitivity underscores the adaptability of lactylation as a cellular signaling modality.

From a therapeutic standpoint, targeting the enzymes responsible for lactylation presents an attractive strategy. Small molecules that inhibit "writers" or activate "erasers" of lactyl groups could modulate gene expression patterns and cellular phenotypes with precision. Additionally, understanding the interplay between lactylation and immune checkpoints may pave the way for innovative immunotherapies, especially in cancer and autoimmune conditions where metabolic dysregulation is prevalent.

Moreover, protein lactylation exemplifies the growing recognition that metabolites are not merely substrates or energy sources but also informational molecules that participate actively in cellular regulation. This realization opens new vistas in the field of metabolomics and epigenetics, bridging gaps between disciplines that historically operated in parallel. The metabolic-epigenetic interface embodied by lactylation exemplifies the multifunctional nature of small molecules in orchestrating biological complexity.

In conclusion, the discovery of protein L-lactylation as a metabolite-driven post-translational modification marks a pivotal advance in cell biology, revealing how metabolic signals are intimately wired to the control of gene expression and protein function. Its roles in physiology and disease extend from the nucleus to the cytoplasm, influencing development, immunity, cancer progression, and cardiovascular health. As research in this domain accelerates, unraveling the full spectrum of lactylation’s molecular mechanisms holds promise for novel diagnostic and therapeutic breakthroughs, transforming our approach to metabolic and epigenetic diseases alike.

Subject of Research: Protein L-lactylation as a post-translational modification regulating metabolic and signaling pathways in physiology and disease.

Article Title: The emerging role of protein L-lactylation in metabolic regulation and cell signalling.

Article References:
Ren, H., Tang, Y. & Zhang, D. The emerging role of protein l-lactylation in metabolic regulation and cell signalling.
Nat Metab 7, 647–664 (2025). https://doi.org/10.1038/s42255-025-01259-0

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s42255-025-01259-0