earth worms

[wolram]

When cut in half they can regrow the severed part, but how?
is the information that enables this re growth encoded in the
DNA, what mechanism initiates this re growth.

[chroot]

I'm no biologist, and all of this is from memory, so it's probably mostly wrong.

AFAIK, body part regeneration is controlled by the Hox genes, which essentially specify where all the body parts should be in an organism. If you take fruit flies and modify their Hox genes, they'll grow legs where their antennae should be, that sort of thing.

The Hox genes are responsible for expressing proteins or hormones that then instruct dividing stem cells in the body to differentiate into a specific kind of tissue. Differentiating cells figure out where they are in the body by essentially sniffing around for these chemical signals to see what's near them.

I also believe I have read that stem cells can be called into action by chemical signals of injury, and actually move through the body to the site of the injury to participate in the healing.

So, I believe the body part continues to grow from these stem cells until the proper location for say, skin is reached. Skin grows there, and the growth goes no further.

- Warren

[marcus]

AFAIK, body part regeneration is controlled by the Hox genes, which essentially specify where all the body parts should be in an organism. If you take fruit flies and modify their Hox genes, they'll grow legs where their antennae should be, that sort of thing.
...
Warren you are a trove of knowledge and an inspiring example:
inorganic techies and astronomers should all know about fruit flies and Hox genes as well
it is fascinating and it would do them good
Bravo.

I remember another detail.
Another thing that helps the severed worm is that
an earthworm (so my 9th grade science teacher told us)
can have multiple hearts----distributed all along its length

It might start out with 5 hearts and then it gets severed into
a piece with 2 and a piece with 3

so the pieces can keep functioning and can both thrive
and go around eating dirt as nature intended
and, in the course of time, grow longer

the earthworm is somewhat modular in design

its other organs including even its thinking apparatus
are distributed along its length, according to my teacher,
in a similarly modular fashion.

[iansmith]

http://www.naturenorth.com/fall/ncrawler/ncrawlF.html

Worms can survive being cut in half! Well, for a little while, at least. It is usually only the head end that will regenerate some segments in the lower end and become a viable worm again. The lower end cannot regenerate a head. However, most often, when cut in half, worms die.


The "brain", "hearts" and other organs are clustered in the head end.

http://www.scaquarium.org/curriculum/iexplore/three_five/units/decompositionI/decomp_background.htm

Earthworms, like seastars, are also capable of regenerating lost body parts. Both the head and the tail of an earthworm can be regenerated, within limits. The extent of regeneration depends on the species, as well as on the position of the "wound" and the size of the worm fragment that remains

I searching to find info on the molecular biology of segment regenration but results have been limited.