Natures wonders: planeria eye regeneration (Introduction)

by David Turell , Thursday, June 25, 2020, 20:34 (1610 days ago) @ David Turell

Almost fully explained by guiding muscle cells:

https://medicalxpress.com/news/2020-06-muscle-cells-guideposts-regenerative-flatworms.html

"Schmidtea mediterranea's eyes are composed of light-capturing photoreceptor neurons connected to the brain with long, spindly processes called axons. They use their eyes to respond to light to help navigate their environment.

***

"...in 2018, Reddien Lab scientist Lucila Scimone found something surprising in adult planarians: groups of mysterious cells that looked like they might play a role in guiding growing axons. She'd noticed this group of cells because they co-expressed two genes not often seen together and some were conspicuously close to the eyes.

"'I was captivated by these cells," she says. They appeared in very small numbers (a normal worm might have around 5; a large one might have up to 10) in every planarian she examined. They were divided into two distinct groups: some around the flatworms' eyes, and others spaced out along the path to the brain center. When she traced the path of existing axons leading from the planarians' eyes to their brain, they coincided with the positions of these cells without exception.

***

"The researchers also created genetically engineered planarians that had the muscle cells, but no eyes, and then transplanted eyes onto their eyeless heads. Sure enough, the neurons grew as normal, snaking towards the cells and then adjusting their trajectories after encountering them.

***

"These findings combined suggested that the cells were fully independent of the visual system—they did not form because of eyes or photoreceptor neurons, but likely established themselves before the neurons grew—which provided more evidence for the guidepost role.

"The guidepost-like activity of these cells then begged the question: how do the cells themselves know where to be? "We found that there's a pattern of signaling molecules in muscle that is setting where these cells should be," Reddien says. "If we perturb the global positional information of the system, these cells get placed in the wrong positions, and then axons go to the wrong positions—so we think there's a positional information framework that places the cells during regeneration, and that allows them to work as guideposts in the correct locations." (my bold)

"At this point, the researchers don't know exactly how the cells are able to communicate with growing axons to serve as guideposts. They could be releasing some sort of signaling molecule that attracts the axons, or they could be communicating by using trans-membrane proteins.

"'That will be an exciting direction for the future," Reddien says. "We have now identified the transcriptome for the cells, which means we know all the genes that these cells express. That provides us with an intriguing list of genes that can be probed functionally, to try to see which ones are mediating the functions of these cells.'"

Comment: interesting that muscle cells are co-opted for this role which is usually by astrocytes. Note in my bold the use of the word 'information' which always disturbs dhw. A perfectly reasonable usage. Not by chance. Design fits.