Biochemistry of cell communication; using viruses (Introduction)

by David Turell , Monday, January 22, 2018, 23:24 (2496 days ago) @ David Turell

A new discovery of cells using virus particles in DNA to communicate information:

https://www.scientificamerican.com/article/cells-hack-viruslike-protein-to-communicate/...

"The genomes of plants and animals are littered with the remains of viruses that integrated themselves into their DNA hundreds of millions of years ago. Most of these viral remnants are inactive, but the latest research suggests that some evolved into genes that let cells communicate.

"A pair of papers published in Cell on January 11 suggest that the protein encoded by one such gene uses its virus-like structure to shuttle information between cells: a new form of cellular communication that may be key to long-term memory formation and other neurological functions.

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"When Shepherd and Budnik analysed the genetic sequences of mouse and fly versions of Arc, they found that they were similar to that of a viral gene called gag. Retroviruses such as HIV use the Gag protein to assemble protective shells called capsids that transport the virus’s genetic material between cells during infection.

"When the researchers looked at the Arc protein under a high-resolution microscope, they found that it formed a similar capsid and carried the genetic instructions, or messenger RNA (mRNA), that encode Arc. The capsid was then wrapped in a piece of the cell membrane and released as an extracellular vesicle.

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"In flies, Budnik’s group found that motor neurons—which connect to muscle cells and tell them when to contract—produced vesicles containing Arc. Once the vesicles reached the muscle cells, they fused with those cells’ membranes, releasing the Arc protein and mRNA. It’s unclear what the muscle cell does with the protein and mRNA, but Budnik found that flies that lacked the gene formed fewer connections between neurons and muscles.

"Shepherd’s group found a similar phenomenon in neurons taken from mouse brains. Neurons that absorbed extracellular vesicles from other neurons would start using the Arc mRNA to produce the protein once they were stimulated to fire.

"Shepherd and Budnik think that the vesicles containing Arc play a part in helping neurons to form and break connections over time as an animal’s nervous system develops or adapts to a new environment or memory. Although the fly and mouse versions of Arc are similar, they seem to have evolved from two distinct retroviruses that entered the species’ genomes at different times. “There must be something really fundamental about it," Budnik says, for it to appear in both mice and flies.

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“'This almost raises more questions than it answers,” says Yvonne Couch, a biologist who studies extracellular vesicles at the University of Oxford in the UK. She wonders what stimulates neurons to produce extracellular vesicles and what other material might be carried between neighbouring cells.

"Shepherd and Budnik plan to continue studying Arc, but they’re also interested in whether other proteins function in the same way. The human genome contains around 100 gag-like genes that could encode proteins that form capsids. It’s possible that this new form of communication between cells is more common than we thought, Shepherd says. “We think it’s just the beginning.'”

Comment: Vescicles contain molecules that carry information. How cells interpret the carried information is not clear. I would suggest that the arrival of the protein starts a cascade of protein reactions until the new function is established. No thought involved, all automatic.