Biological sciences researchers from the U of A have led publication of a paper that expands our understanding of sensory neurons in the tentacles of sea anemones, linking them to kidney disease in humans through a common gene. 

Analysis of the evolutionary roots of the human ability to hear led the team to closely examine the mechanosensory hair cells found on the outside of the tentacles of the sea anemone. Mechanosensation relates to the ability to hear and to sense touch, while hair cells are auditory cells in the vertebrate inner ear that pick up vibrations to enable hearing. Sea anemones have similar-looking cells on their tentacles — also called hair cells — that they use to sense the movements of their prey.  

In the paper published in Nature Communications, led by corresponding author Nagayasu Nakanishi, an associate professor of biological sciences at the U of A, researchers found that the gene responsible for kidney disease in humans — polycystic kidney disease 1 (or PKD-1) gene — is also present in anemones, allowing their hair cells to detect water movement in their environment and facilitate a response.  

Because PKD-1 functions as a fluid sensor in kidney cells and is necessary for hearing in mammals, this new finding suggests an evolutionarily ancient role for PKD-1 in sensing fluid movement predating the common ancestor of mammals and sea anemones living more than 580 million years ago.  

Cnidarians, which include jellyfish, corals and sea anemones, are the closest living relatives of animals with bilateral symmetry, such as humans and insects. Though creatures like sea anemones are often assumed to be lacking the sophistication and complexity present in vertebrates, they share many of the same genes as humans, including those responsible for essential functions and serious diseases.  

3D reconstruction of sea anemone neurons

As such, cnidarians are useful for studying human evolutionary history because features shared by bilateral animals and cnidarians were likely present in our last common ancestor. A feature of note is the mechanosensory system, and both bilaterians and cnidarians use similar sets of genes in mechanoreceptor development. 

Unexpectedly, researchers also found that there is not only a single type of mechanosensory neuron on the surface of the anemone tentacle, as previously assumed, but instead at least two unique types of hair cells. The presence of multiple types of mechanosensory neurons present in animals belonging to a group diverging from ours over 580 million years ago suggests that the mechanosensory system of our ancient shared ancestor may be more complex than previously thought, or that cell type diversity of mechanosensory neurons has increased independently in sea anemones and related marine stingers like jellyfish. These discoveries represent a significant step in continued research into the basic foundations of human mechanosensation and the evolution of animal mechanosensory systems.  

"This paper is the product of years of research conducted by undergraduate and graduate students along with our mentor, Dr. Nakanishi," said Baranyk, a Ph.D. student in biological science who was first author on the paper. "It is so rewarding to see everything come together so that this work can be shared as a contribution to scientific knowledge and to inspire future investigations." 

Nakanishi added: "I am thrilled to see our team's efforts — after many 'failed' experiments and some successful ones — paid off. It is always rewarding to witness students gradually mature as scientists, make new discoveries and use the experiences to find paths to even greater things." 

Five of the six co-authors on the paper are affiliated with the U of A. In addition to Baranyk and Nakanishi, Miguel Silva was an M.Sc. student in biological sciences, while two other co-authors, Kristen Malir and Sakura Rieck, were undergraduates working in the Nakanishi Lab at the time the research was conducted. Gracie Scheve was a visiting undergraduate scholar in the Nakanishi lab. Silva and Malir have since graduated.