A strange genetic link between humans and sea anemones has just been confirmed
A gene linked to hearing development in humans has also just been linked to sensory development in sea anemones.
Called louse-iv (pow-four), the gene is found in the tentacles of the starlet sea anemone (Nematostella vectensis), where it plays a crucial role in the animal’s sense of touch.
Cnidaria, the phylum to which sea anemones belong, is the closest relative of Bilateria, animals with bilateral symmetry such as humans, diverging from their last common ancestor who lived around 748 to 604 million years ago. .
Finding the role of the gene in the starlet sea anemone suggests that it was present in their common ancestor and likely played a role in sensory development back then as well.
“This study is exciting because it has not only opened up a new field of research into how mechanosensation develops and functions in a sea anemone…it also informs us that the building blocks of our sense of hearing have ancient evolutionary roots dating back hundreds of millions of years to the Precambrian,” said biologist Nagayasu Nakanishi from the University of Arkansas.
In humans and other vertebrates, the sensory receptors in the auditory system are called hair cells. These cells have bundles of finger-like organelles called stereocilia that sense mechanical stimuli; namely, the vibrations we hear as sound. In mammals, louse-iv is necessary for the development of hair cells; we know this because the mice that have had louse-iv knocked out are deaf.
The starlet sea anemone has similar mechanosensory hair cells on its tentacles, used to detect movement. However, little was known about the anemone louse-iv gene and what role, if any, it played in sensory development.
A team of researchers led by biologist Ethan Ozment from the University of Arkansas wanted to figure out what the gene was doing. The best way to do this is to turn off the gene using the CRISPR-Cas9 gene editing tool and observe the changes. So that’s what the team did.
They injected a cocktail containing the Cas9 protein into fertilized starlet sea anemone eggs to cut the louse-iv gene, and studied developing embryos, as well as cultured and mutated anemones.
Compared to wild-type control anemones, the mutant animals showed abnormal tentacular hair cell development and showed no response to touch. Without louse-ivanemones were unable to sense mechanical stimuli via their hair cells.
Moreover, knock out louse-iv in anemones has significantly deleted a gene very similar to the one that makes polycystin 1 found in vertebrates, where it is required for the detection of fluid flow through the kidneys. Sea anemones may not have kidneys, but sensing liquid flow would be a useful ability for marine animals.
Together, the researchers said, the results suggest that louse-iv played a role in the development of mechanosensory cells in the common ancestor between Cnidaria and Bilateria. However, to trace the gene even further will require data from other phyla with earlier points of divergence.
Our results indicate that the role of louse-iv in mechanoreceptor development is largely conserved across Cnidaria and Bilateria,” the researchers wrote in their paper.
“How long has the role of louse-iv in mechanoreceptor differentiation that arose in animal evolution remains unresolved and requires comparative data on placozoans and sponges, which are lacking.
The research has been published in eLife.