Humans and sea anemones have an amazing genetic link

The study of cnidarians – a group of radially symmetrical animals such as corals, jellyfish and sea anemones – can provide valuable information about the history of human evolution. And for good reason: they are the closest living relatives of bilaterals, which have right-sided and left-sided, that is, the vast majority of animals, including humans. Thus, the characteristics shared by both groups were likely present in the genome of our last common ancestor, who lived from about 748 to 604 million years ago. For example, cnidarians and bilaterians use very similar sets of genes to develop their nervous systems. Researchers report in electronic life that a particular gene plays a major role in the development of tactile sensations.

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Gene required for hair cell development

Hair cells are sensory cells that line the inner ear of vertebrates; they are part of both the auditory and vestibular systems (the latter contributing to the sense of movement and balance). They pick up vibrations of sound waves, amplify them and convert them into nerve impulses.

As far as we know, anemones are not endowed with auditory abilities; however, they have similar cells, also called hair cells, throughout their tentacles. They are used to detect the movements of their prey. ” Hair cells of cnidarians have morphological and functional characteristics similar to those of mechanosensory cells of other animal lines. ‘, the researchers write. electronic life.

Previous research has shown that in mammals, the POU-IV gene is required for the proper development of hair cells. In humans, mutations at one of the POU-IV loci have been associated with hearing loss, and in mice genetically engineered to inhibit the expression of this gene, auditory and vestibular hair cells fail to complete their differentiation and eventually die. Scientists knew that sea anemones also had this gene, but no one had ever investigated how it was involved in the development of their hair cells.

To shed light on the role played by the POU-IV gene in sea anemones, the researchers neutralized the gene in the animal’s fertilized eggs using the CRISPR-Cas9 gene-editing tool. They found that this operation resulted in abnormal development of tentacle hair cells: the modified anemones lacked touch, which was shown when compared with a control group of unmodified anemones that continued to respond to tactile stimuli with local anemone contraction. longitudinal muscles.

loss of sense of touch

Behavior of wild-type (A, B) and genetically modified (C, D) Nematostella vectensis polyps in response to tactile stimuli from their tentacles. The latter caused wild individuals to retract their tentacles, while most mutants were insensitive to touch. Image Credit & Copyright: N. Nakanishi et al., eLife (2022)

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A rumor with very ancient roots

The team also found that inhibition of POU-IV significantly suppresses a gene very similar to that produced by polycystin 1, a protein found in vertebrates, that is required for normal perception of fluid flow through kidney cells. True, sea anemones do not have kidneys, but it can be assumed that the detection of fluid flow is of particular interest to this marine animal.

The POU-IV gene is common to all existing groups of animals, with the exception of ctenophores, planktonic, transparent, rotationally symmetrical marine organisms, which indicates the early appearance of this gene in animal evolution. The results of this study suggest, in particular, that this gene plays a very ancient role in the development of tactile sensations, dating back at least to the last common ancestor of cnidarians and bilaterians. The team notes that this is the first discovery of a gene regulatory factor required for the development of classical mechanosensory neurons in an early evolving group of non-bilateral animals.

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This study is exciting because it not only opens up a new area of ​​research into how mechanosensing develops and functions in sea anemones, with great potential for new and important discoveries (which will be reported in the future), but also informs us. that the building blocks of our hearing have ancient evolutionary roots dating back hundreds of millions of years to the Precambrian. said Nagayasu Nakanishi, a biologist at the University of Arkansas and co-author of the study.

The researchers note that more data is needed to trace the exact origin of this gene, especially genetic data from earlier phyla such as placozoans and sponges.

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