Origin of sense of smell identified

Washington, Mar. 26 : When our noses pick up a scent, whether the aroma of a sweet rose or the sweat of a stranger at the gym, two types of sensory neurons are at work in sensing that odour or pheromone.

These sensory neurons are particularly interesting as they are the only neurons in our bodies that regenerate throughout adult life-as some of our olfactory neurons die, they are soon replaced by newborns.

Previous hypotheses about the origin of these olfactory nerve cells have given credit to embryonic cells that develop into skin or the central nervous system, where ear and eye sensory neurons, respectively, are thought to originate.

Biologists at the California Institute of Technology (Caltech) led by an Indian origin researcher have now found that neural-crest stem cells-multipotent, migratory cells unique to vertebrates that give rise to many structures in the body such as facial bones and smooth muscle-also play a key role in building olfactory sensory neurons in the nose.

The two main types of sensory neurons in the olfactory system are ciliated neurons, which detect volatile scents, and microvillous neurons, which usually sense pheromones.

Both of these types are found in the tissue lining the inside of the nasal cavity and transmit sensory information to the central nervous system for processing.

In the new study, the researchers showed that during embryonic development, neural-crest stem cells differentiate into the microvillous neurons, which had long been assumed to arise from the same source as the odor-sensing ciliated neurons. Moreover, they demonstrated that different factors are necessary for the development of these two types of neurons.

By eliminating a gene called Sox10, they were able to show that formation of microvillous neurons is blocked whereas ciliated neurons are unaffected.

They made this discovery by studying the development of the olfactory system in zebrafish-a useful model organism for developmental biology studies due to the optical clarity of the free-swimming embryo.

"A key question in developmental biology-the extent of neural-crest stem cell contribution to the olfactory system-has been addressed in our paper by multiple lines of experimentation," Ankur Saxena, a postdoctoral scholar in Albert Billings Ruddock Professor of Biology at Caltech Marianne Bronner's laboratory and lead author of the study, said.

The paper has been published in the journal eLIFE.

--ANI (Posted on 26-03-2013)

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