AI Insight
Researchers created a comprehensive single-cell transcriptome atlas of the jellyfish Aurelia coerulea, revealing how cell types change during the transformation from the sessile polyp stage to the free-swimming medusa stage. The transition involves increased cellular diversity, including expansion of neural subtypes and emergence of striated muscle cells, with some neuronal lineages dating back approximately 500 million years to the common ancestor of medusozoans and anthozoans. Analysis of muscle types shows that jellyfish striated muscles regulate contraction similarly to smooth muscles in both cnidarians and bilaterians, suggesting that smooth muscle contraction regulation is ancestral and troponin-based regulation in striated muscles evolved only in bilaterians.
Why it matters
This work provides fundamental insights into the evolution of muscle types and nervous systems across animal lineages, helping to understand when and how key cellular innovations arose. The findings challenge previous assumptions about muscle evolution and offer a framework for studying tissue differentiation and life cycle transitions in early-diverging animal groups.
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by Oliver Link, Stefan M. Jahnel, Kristin Janicek, Daniel Guerguerian, Johanna Kraus, Juan D. Montenegro, Bob Zimmermann, Brittney Wick, Konstantin Khalturin, Alison G. Cole, Ulrich Technau
The life cycle of most medusozoan cnidarians is marked by the metagenesis from the asexually reproducing sessile polyp and the sexually reproducing motile medusa. At present, it is unknown to what extent this drastic morphological transformation is accompanied by molecular changes in the cell type composition. Here, we provide a single-cell transcriptome atlas of the cosmopolitan scyphozoan Aurelia coerulea focusing on changes in individual cell states during the transition from polyp to medusa. Notably, this transition is marked by an increase in cell type diversity, including an expansion of neural subtypes and the appearance of striated muscles. We find that two families of neuronal lineages are specified by homologous transcription factors in the sea anemone Nematostella vectensis and A. coerulea, suggesting an origin in the common ancestor of medusozoans and anthozoans about 500 Myr ago. Our analysis suggests that gene duplications might be drivers for the increase of cellular complexity during the evolution of cnidarian neuroglandular lineages and highlights the close relationship of neurons and muscles. One key medusozoan-specific cell type is the striated muscle in the subumbrella. Evaluating muscle types by fiber anatomy and gene expression validation of their individual molecular profiles made it possible for the first time to investigate transcriptome differences between smooth and striated muscles. Although smooth and striated muscles are phenotypically different, both have a similar regulation of the contractile complex, reminiscent to the regulation of smooth muscles in bilaterians. This contrasts with bilaterian striated muscles, where the regulation of muscle contraction involves Ca2+ binding troponins and their interaction with Tropomyosin. These data suggest that smooth muscle contraction regulation is ancestral and the use of troponins in striated muscles only evolved in bilaterians.