Scientists discover the genetic origin of our senses

Diagram of genetic codes

A research group from the University of Innsbruck has discovered how the cranial sensory ganglia are formed.

University of Innsbruck researchers have identified the genetic origin of our senses

Researchers from the University of Innsbruck have determined the genetic origin of our senses. The results reveal that sensory ganglia in the vertebrate skull arise from a genetic program shared with its closest living relative, the cormorant.

It definitely pays to have a head. This may seem obvious, but evolution has taken a long journey to test it: Invertebrates initially dominated the water when animal life began to emerge. Although vertebrates already had head features, they eventually succeeded because they developed a new, superior head. This “new head” allowed a spatial diffusion and extensive proliferation of sensory cells, which improved the perception of the surrounding environment. This was also crucial to the evolution of the predatory lifestyle.

The cranial sensory ganglia are essential for transmitting external sensations to the vertebrate brain. You can think of them as ganglia that spread throughout the brain and collect information from the sensory organs. The exact process by which these nodes were created was unknown to scientists until this point. These questions are finally resolved by a study published in Nature on May 18, 2022.

bipolar tail neurons

An embryo from the tunica Ciona intestinalis. The micrograph shows bipolar neurons in the tail region (green) and epidermal cells (purple). Credit: Alessandro Benatti

vertebrate prototype

The research group of Ute Rothbächer of the Institute of Zoology in University of Innsbruck He decisively participated in the final phase of the project, an international collaboration of several institutions, designed by Oxford university. Their findings show that vertebrates’ cranial sensory ganglia emerge from a genetic program also present in their closest living relative, the tunica. In stick larvae, some sensory neurons, called tail bipolar neurons, are located in the tail region. These external stimuli act, but they are also responsible for the movement of the animal. In both animal subphyla, the respective structures are formed by the Hmx gene.

“The bloopers are like an evolutionary model for vertebrates,” Rothbacher explains. “There is a large anatomical gap between the adults of this subphyla, as they adapt to ecological niches. This complicates the search for their evolution. Shared structures and mechanisms can only be identified at the embryonic stage – our common ancestor was probably very similar to the tunica larva.”

The model organisms for the study were the lamprey, a primitive eel-like fish often referred to as a ‘living fossil’, and the Tunicate Ciona intestinalis, which is surrounded by a yellowish tubular covering that protects the animal and purifies food.

conserved gene

Alessandro Benatti, a doctoral student in the Rothbacher research group, provided crucial data on the function of the Hmx gene in Siona. He applied the CRISPR-Cas9 gene technology to selectively output gene sequences, while the transient transgene method was used to overexpress the genes.

The researchers found that Hmx controls the development of tail bipolar neurons in tunicates, while in vertebrates, it does so for the cranial sensory ganglia. Surprisingly, the introduction of Hmx lamprey gene segments into Ciona[{” attribute=””>DNA were similarly active as Ciona’s own Hmx.

“Hmx has been shown to be a central gene that has been conserved across evolution. It has retained its original function and structure and was probably found in this form in the common ancestor of vertebrates and tunicates,” Pennati explains. Cranial Sensory Ganglia and Bipolar Tail Neurons thus have the same evolutionary origin, Hmx was probably crucially involved in the formation of highly specialized head sensory organs in vertebrates.

Reference: “Hmx gene conservation identifies the origin of vertebrate cranial ganglia” by Vasileios Papadogiannis, Alessandro Pennati, Hugo J. Parker, Ute Rothbächer, Cedric Patthey, Marianne E. Bronner, and Sebastian M. Shimeld, 18 May 2022, Nature.
DOI: 10.1038/s41586-022-04742-w