Introducing the brain: how neurons sense smells (Introduction)

by David Turell , Wednesday, December 20, 2023, 17:21 (128 days ago) @ David Turell

A genetic study:

https://medicalxpress.com/news/2023-12-sensory-magic-emerges-mechanism-tailors.html

"The mammalian nose is a work of evolutionary art. Its millions of nerve cells, each tailored with just one of thousands of specific odor-chemical receptors encoded in the genome, can collectively distinguish a trillion distinct scents. Those sensations, in turn, inform many behaviors, from assessing food options to discerning friends from foes to sparking memories.

"In the journal Nature, a research team led by scientists at Columbia's Zuckerman Institute describes a previously undetected mechanism in mice—starring the genetic molecule RNA—that could explain how each sensory cell, or neuron, in mammalian noses becomes tailored to detect a specific odor chemical.

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"In their study, Dr. Lomvardas and his team uncover details of the final stage of this process when the winner emerges from the finalist genes.

"'It's basically a battle between a 1,000 contenders," said Ariel Pourmorady, the paper's first author and an M.D.-Ph.D. candidate at the Zuckerman Institute in the Lomvardas lab.

"The action is exceedingly complex and involves a dizzying cast of molecular characters. Playing roles that either dial up or down each gene's ability to produce olfactory receptors are a variety of gene-regulating molecules. By gathering into various alliances within the genome, these molecular players help turn specific genes on or off.

"Also in the fray is another set of molecular hubs that reshape portions of the genome in ways that favor specific receptor genes. When his team first observed these in the genome in 2014, Dr. Lomvardas dubbed them "Greek Islands" because they reminded him of islands in the Aegean Sea.

"'It turns out that the genome has a certain spatial organization in the nucleus and changes in this structure are pivotal when it comes to which genes are expressed into proteins, like olfactory receptors," said Pourmorady. "We are learning just how important this process is within maturing olfactory cells."

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"'It looks like the RNA the cell makes during gene expression also is altering the genome's architecture in ways that bolster the expression of one olfactory receptor gene while also shutting down all the others," Pourmorady said.

"Big gaps in this genome-controlling story remain, but the researchers say the outline is becoming more defined. It starts with maturing olfactory cells, which initially express many receptor genes at those genomic hubs where gene-regulating molecules and complexes, including Greek Islands, converge.

"Then the RNA winnows the contending olfactory-receptor genes down to one. The particular hub in each cell where the molecular stars align to produce the highest amount of RNA wins the competition. At this hub, receptor-gene expression soars. But, like a slinky saboteur, RNA from that same hub may wind its way to all the other hubs. In those locations, the RNA causes shape changes in the genome that shut down gene expression. The result is a nose's worth of mature olfactory neurons, each of which bears on its surface only one odorant receptor."

Comment: The previous paper showed a protein level of control and this paper studies genes, and the effect of RNA activating expressions.