Decoding the genes behind jellyfish movement

Dong, Z., Wang, F., Liu, Y. et al. Genomic and single-cell analyses reveal genetic signatures of swimming pattern and diapause strategy in jellyfish. Nat Commun 15, 5936 (2024). https://doi.org/10.1038/s41467-024-49848-z

Movement is everything

If you go to any aquarium, in addition to the touch tanks, the sharks, and the moray eels, you’ll often notice visitors gathered around a circular jellyfish tank, drawn in by their elegant, calming motion. 

How do jellyfish move and orient themselves in the environment? Despite their simplicity, jellies have surprising complexity beneath the “bell”, the dome shaped part that makes up most of the body.

Movement, or locomotion, drives biology in many ways. It requires balance, perception of pressure, and orientation of oneself in the environment. The structures responsible for balance range from simple mechanical organs in invertebrates, to complex inner ears in mammals. If you’ve ever blown your nose too hard, you know that a small shift in your inner ear can throw off your sense of balance and make it difficult to move. 

Ancient simplicity, hidden complexity

Jellyfish are ancient yet simple species with basic muscles and nervous systems. Their early presence in the geologic record makes them a unique organism for the study of the evolution of locomotion.

Jellyfish have simple mechanical organs called “statocysts”, located around the bell, that respond to gravity, helping the animal orient itself in three-dimensional space. Like the bubble in a level, the “statolith”, a small rock-like structure, inside the statocyst moves with the jellyfish’s orientation, interacting with sensory hair cells.

The presence of statocysts and hair cells is essential for jellyfish swimming patterns, but their underlying genetic basis remains unclear. 

A genetic basis for movement

Researchers in China investigated jellyfish movement, focusing on two species: T. rubra, a species that lacks a statocyst and swims in a straight vertical motion, and A. coerulea, a free-swimming species capable of movement in any direction.

To begin, they assembled the genomes for these two species, which is the collection of all genes in the given organism, and put together a phylogenetic tree of jellyfishes (similar to a family tree, but where each branch is a different species). T. rubra is most closely related to immobile species that live on the ground in aquatic environments. Meanwhile, A. coerulea is closely related to other “classic” jellyfish such as the moon jelly, A. aurita. Upon making this gelatinous family tree, the researchers determined that T. rubra diverged from the other jellies ~330 million years ago. 

Next, they looked at the genes themselves. To start, they focused on genomics, or simply the list of genes present in different cells. Since hair cells play a crucial role in statocyst formation and operation, they focused on hair cells in the sensory organs of the two jellies and identified several key differences. While T. rubra lack a statocyst, they have more primitive rhopalia, a sensory organ that can detect light, help with balance, and has its own “hair”-like cells. 

Notable genes were absent in T. rubra hair cells that were then specifically expressed in those found in the statocysts of A. coerulea including CFAP141, TRPC4, CACNA1E, LOXHD1, and KIF13B. 

These genes are mainly linked to motor activity and the dynein complex, a group of proteins essential for hair cell health and function. T. rubra, lacking these genes, has more limited hair movement.

Hair cell motility and how to tell which way is up

Hair cell (or “ciliary”) motility is crucial for statolith formation and function. In A. coerulea, ciliary motility genes were highly expressed, reflecting the presence of a statocyst, unlike in T. rubra.

Finally, the authors looked at the transcriptomics or the gene expression levels in the hair cells of the sensory organs in each species. They found that the dynein family genes, important for protein transport, were more expressed in A. coerulea. These are essential for forming the statoliths—small structures made of calcium, sugars, and proteins. 

In A. coerulea, the genes that help build and move the materials for statoliths were much more active compared to T. rubra, which doesn’t have a statocyst. This same group of genes is even more prominent in C. xamachana, a jellyfish known for its upside-down swimming, emphasizing the statocysts importance for movement and orientation.

To summarize, the free-swimming pattern seen in A. coerulea requires extra genes to support its statocyst. These help the jelly to orient itself in the ocean environment, and collect the materials needed for its sensory organs. While the straight vertical movement of T. rubra is still calming, the ability of A. coerulea to move anywhere highlights the jellyfish trait that we all admire.

The ethereal grace of jellyfish may be simple, but beneath the surface, their movement depends on a hidden network of genes and pathways – delicate machinery that endures these creatures as symbols of grace and fascination in our oceans. 

Cover photo by Rhinopias via Wikimedia Commons

Josiah Grzywacz

I’m a former oceanographer with an MSc in Biological Oceanography from UConn where I studied mixotrophy in marine ciliates. After a year in Poland (studying freshwater critters) I moved to California. I currently work as a lab technician at Stanford. Outside of science, I enjoy a good book, a long run, and frozen fruit.