Whitton, L. | Search bioRxiv

bioRxiv2026

Stable yet Shifting: Early Toxin Dynamics in Typical and Atypical Clownfish-Anemone Symbioses

Among venomous animals, cnidarians represent the oldest metazoan lineage in which venom production and a specialized delivery system are defining synapomorphies. Cnidarians also represent the only venomous lineage for which mutualistic symbioses have evolved resulting in scenarios where mutualistic symbionts may also be targets of their venom. The most iconic example of this relationship is the mutualism between clownfish and their venomous sea anemone hosts. To investigate how symbiont presence and establishment influence toxin gene expression, we used a comparative TagSeq and RNA-Seq approach to quantify venom gene dynamics during the first 48 hours of clownfish-anemone symbiosis establishment in five anemone species. Our taxonomic sampling included three typical hosting species (Entacmaea quadricolor, Radianthus crispa, and Stichodactyla haddoni), each representing distinct evolutionary lineages of clownfish hosts, and two atypical Caribbean species (Condylactis gigantea and Stichodactyla helianthus) that do not host clownfish in nature, but have reported to host within the aquarium trade. Tentacle samples were collected prior to hosting, approximately 12 hours after initial symbiont establishment, and again 48 hours after symbiosis establishment. Our analyses revealed that overall toxin assemblages remained relatively stable during the early establishment phase, with no significant changes in the most highly expressed toxin gene candidates. However, subtle transcript-level shifts occurred within multi-copy toxin gene families, including cytolytic actinoporins and Sea Anemone 8 (SA8)-like toxins. Notably, one C. gigantea actinoporin transcript exhibited a [~]600-fold increase in expression in a single individual, which coincided with two clownfish mortalities prior to successful association, which subsequently decreased after establishment. Comparative sequence alignments suggest that amino acid substitutions in this transcript may be functionally relevant to symbiosis intolerance, as the amino acid substitutions were unique to this transcript, and not found in any other previously described cytolytic actinoporin. Together, these findings reveal that early toxin gene expression in clownfish-hosting sea anemones is largely stable, yet subtly dynamic at the transcript level. This study provides the first comparative transcriptomic insights into the molecular processes shaping symbiosis establishment in clownfish-anemone mutualisms, offering a framework for understanding venom evolution in the context of co-evolutionary interactions. HighlightsO_LIComparative gene expression survey reveals relatively stable toxin assemblages throughout the first 48 hours of establishing clownfish-anemone symbiosis. C_LIO_LISubtle shifts were observed among transcript variants in multi-gene copy variants, with potential implications for barriers to establishing symbiosis. C_LIO_LIAlthough toxin assemblages varied among species, sea anemone 8 (SA8) toxin-like transcripts were highly abundant in four of the focal taxa. C_LIO_LIThis is the first comparative gene expression analysis investigating molecular processes surrounding symbiosis establishment between clownfish and sea anemones. C_LIO_LIThese results provide insight into toxin dynamics surrounding the establishment of symbiosis, with particular insights into key evolutionary transitions resulting in symbiosis among atypical clownfish hosting species. C_LI

genetics↗

bioRxiv2019

Genes influenced by MEF2C contribute to neurodevelopmental disease via gene expression changes that affect multiple types of cortical excitatory neurons

Myocyte enhancer factor 2 C (MEF2C) is an important transcription factor during neurodevelopment. Mutation or deletion of MEF2C causes intellectual disability (ID) and common variants within MEF2C are associated with cognitive function and schizophrenia risk. We investigated if genes influenced by MEF2C during neurodevelopment are enriched for genes associated with neurodevelopmental phenotypes, and if this can be leveraged to identify biological mechanisms and individual brain cell types affected. We used a set of 1,052 genes that were differentially expressed in the adult mouse brain following early embryonic deletion of Mef2c in excitatory cortical neurons. Using GWAS data, we found these differentially expressed genes (DEGs) to be enriched for genes associated with schizophrenia, intelligence and educational attainment but not autism spectrum disorder (ASD). Using sequencing data from trios studies, we found these DEGs to be enriched for genes containing de novo mutations reported in ASD and ID, but not schizophrenia. Using single cell RNA-seq data, we identified that a number of different excitatory glutamatergic neurons in the cortex were enriched for these DEGs including deep layer pyramidal cells and cells in the retrosplenial cortex, entorhinal cortex and subiculum. These data indicate that genes influenced by MEF2C during neurodevelopment contribute to cognitive function and risk of neurodevelopmental disorders. Within excitatory neurons, common SNPs in these genes contribute to cognition and SZ risk via an effect on synaptic function based on gene ontology analysis. In contrast, rare mutations contribute to earlier onset ASD and ID via an effect on cell morphogenesis. Author SummarySchizophrenia is a complex disorder caused by many genes. Current drugs for schizophrenia are only partially effective and do not treat cognitive deficits, which are key factors for explaining disability. Here we take an individual gene identified in genetic studies of schizophrenia and cognition called MEF2C, which on its own is a very important regulator of brain development. We use data from a mouse study where MEF2C has been stopped from functioning or knocked out during brain development. The effect of that knock out has been measured when the mice reach adulthood, in the form of a set of differentially expressed genes (DEGs) from the somatosensory cortex. We found that this set of DEGs contains more genes than expected by chance that are associated with schizophrenia and cognition or contain rare new (de novo) mutations reported in autism and intellectual disability. Using gene expression data from single brain cells, we identified that a number of specific excitatory glutamatergic neurons in the cortex were enriched for these DEGs. This study provides evidence that the molecular mechanisms that underpin schizophrenia and cognitive function include disruption of cell types influenced by MEF2C.

genomics↗