A lovely marine creature with a jelly-like physique surrounded by iridescent combs. The almost certainly candidate for the earliest branched-off animal lineage. And now, an unimaginable nervous system. Comb jellies could also be too small to even trigger ripples within the water as they swim, however their distinctive options are creating shockwaves within the scientific group.

A current study, revealed in Science, seemed intently on the nerve-net neurons of comb jellies and located that as an alternative of being linked by synapses – junctions between neurons in all different animals, together with people – they’re constantly linked by a single plasma membrane.

Comb jellies, or ctenophores, belong to phylum ctenophora, and are one of many oldest animal lineages with an outlined nervous system. They’re fairly laborious to tradition within the lab, nonetheless, but Pawel Burkhardt managed to just do the factor in his lab on the Michael Sars Centre on the College of Bergen, Norway.

“This was something that all came together, step by step. We were able to basically disentangle the nervous system,” Dr. Burkhardt informed The Hindu.

He had collaborated with Maike Kittelmann of the Oxford Brookes College within the U.Okay. beforehand for a study, revealed in Present Biology in 2021. On this research, they examined a single neuron within the nerve-net utilizing excessive decision electron microscopy. They discovered that the neurites – the branches from the neuron that type synapses – have been all interconnected by a single plasma membrane, a characteristic not seen within the neurons of different animals.

For the brand new research, they wished to see how a single nerve-net neuron may make connections with different nerve-net neurons. After they noticed the microscopy pictures of the completely different nerve-net neurons collectively, they have been taken fully unexpectedly.

“We expected synapses,” mentioned Dr. Kittelmann. “We went in there to find the synapses between the nerve-net neurons, but we just couldn’t find them, because they aren’t there.”

The researchers performed their experiments with ctenophores within the predatory cydippid stage, an earlier stage within the ctenophore life cycle when it’s able to reproducing. They used high-pressure freezing and fixing and electron microscopy to construct a 3D view of all of the neurons throughout the nervous system of ctenophores.

After they examined how some neurons linked to others within the cydippid, they discovered synaptic connections. However the 5 neurons throughout the nerve-net appeared to all be interconnected by way of a syncytial community, i.e. with none synapses.

In an ironic twist, the brand new research once more demonstrated the usefulness of extra superior microscopy methods to point out that in ctenophores, at the least within the nerve-net neurons, it’s the other: it’s a syncytium.

Ctenophores have been on the centre of a heated debate over the id of the primary animal. Entire-genome sequencing research of ctenophores, revealed in 2013 in Science and 2014 in Nature, added proof to the speculation that ctenophores have been the earliest department of the animal kingdom and type a sister group to all different animals.

However even when ctenophores represent the oldest animal lineage, biologists are nonetheless unclear as to how their nervous system advanced. Based mostly on his findings within the 2014 Nature paper, Leonid Moroz of the College of Florida proposed a controversial principle. He mentioned that the nervous system may have advanced twice, as soon as in ctenophores and as soon as in different animals.

His paper and one other study that adopted pointed to ctenophores having a novel nervous system. The ctenophore genome didn’t present classical neurotransmitter pathways current in different animals nor did ctenophore neurons specific the frequent genes related to different animal neurons.

“Our paper is not proof for or against the independent evolution of the ctenophore nervous system,” Dr. Burkhardt mentioned. “However, given that ctenophores are very early branching animals and that the nerve-net architecture of ctenophores is unique, it is possible that the nerve-net evolved independently.”

In response to him, the truth that ctenophores use cilia, and never muscle mass, to maneuver is also a motive why they may evolve a special sign conduction system.

“It is a fantastic finding that nerve-nets can also be syncytial,” mentioned Detlev Arendt, a researcher on the European Molecular Biology Laboratory who research the evolution of nervous methods. “We have to understand how such a nerve-net operates as compared to other nerve-nets that are connected with synapses or gap junctions.”

Dr. Burkhardt and Dr. Kittelmann are eager to check the nerve-net neurons because the ctenophores develop, to see if grownup ctenophores retain the syncytial nerve-net or in the event that they develop synapses.

For Dr. Moroz, the outcomes are extra proof for the ctenophore nervous system’s distinctive nature and indicators that it may have advanced independently. Extra importantly, he pressured the significance of such research in a broader context – of how distinctive animal methods just like the ctenophore might help us perceive how the nervous system has advanced to work so completely, even in people.

“Nature has offered to us alternate unique examples of how to get the same outcome in different ways,” Dr. Moroz mentioned. “The shortcut to understand the fundamentals of neuronal function and treat a variety of disorders will come from comparative analyses.”

There’s much more to do to additional perceive the purposeful and evolutionary significance of the syncytial nerve-net neurons in ctenophores. This research gives an vital anchor for such analysis into nervous system evolution in animals, analysis which Dr. Moroz firmly believes is crucial to know the ideas of mind operate.

“To understand our brain, we have to understand alternate strategies,” he mentioned. “To understand our brain, we have to study small creatures in the sea.”

Rohini Subrahmanyam is a contract journalist.