Discovery of a new cellular element crucial to sense of smell

Researchers at Umeå University have found an organelle, a previously unidentified cellular component, inside the neurons that are responsible for the ability to smell. The finding might have repercussions for future studies on COVID-19 symptoms like impaired smell sense.

A prerequisite for finding a treatment for impaired sense of smell is to first understand how the sense of smell works.”

Staffan Bohm, Professor, Department of Molecular Biology, Umeå University

What the researchers have found is an organelle that has never before been seen inside nerve cells. Researchers have given the newly identified organelle the name multivesicular transducosome. The unique microscopy infrastructure at Umeå University was instrumental in the discovery.

Organelles are distinct “workstations” within cells that are similar to the various body organs in that they each serve a unique purpose within the cell. The majority of organelles are shared by various cell types, but some organelles have particular functions that are found only in particular cell types.

Long projections, known as cilia, protrude from olfactory nerve cells into the nasal cavity, where they contain the proteins that bind odorous substances and trigger nerve impulses to the brain. Transduction is the process of turning smells into nerve impulses, and the newly discovered organelle only contains transduction proteins.

The transductosome’s task is to store transduction proteins and maintain their separation from one another until they are required. The organelle’s outer membrane bursts in response to olfactory stimulation, releasing the transduction proteins so they can get to the cilia of the neuron and causing the perception of a smell.

The researchers also found that a protein known as retinitis pigmentosa 2 (RP2), which is normally known to control transduction in the eye’s photoreceptor cells, is carried by the transductosome. Retinitis pigmentosa is a type of eye disease that harms the light-sensitive cells in the eye and can be brought on by mutations in the RP2 gene.

Bohm added, “A question for further research is whether the transductosome has a role in vision and whether it is present in brain neurons that are activated by neurotransmitters and not light and smell. If so, the discovery may prove even more significant.”

Devendra Kumar Maurya, a researcher, used an innovative method called correlative microscopy to find the transducosome. The method combines electron and confocal microscopy to image both the internal structures of a cell and the locations of various proteins at once.

Devendra’s method development, which made it possible to use the technique to analyze whole neurons in tissue sections, was crucial to the discovery.