Mike the Mad Biologist

axolotl
Where’s axolotl?
(Credit: Jan-Peter Kasper/EPA/CORBIS)

Often, biologists talk about model systems: organisms that are particularly useful for research. One such organism is the axotol, Ambystoma mexicanum, a cool, but weird salamander:

Because of their large egg and embryo size, susceptibility to tissue grafting, and ability to regrow severed limbs and tails, “axolotls have a long history as primary amphibian models, especially in research areas involving embryonic development,” says Voss. He calls them a “re-emerging model organism” for scientists who study them with gene expression and other new tools. For example, cell and developmental biologist Elly Tanaka of the Center for Regenerative Therapies at the Dresden University of Technology in Germany says her lab was able to develop and breed transgenic axolotls, which “makes it easier to study the mysterious process of regeneration on a molecular level by driving gene expression in regenerating tissues.”

When a salamander regrows its severed tail, it must regenerate a portion of the spinal cord and the neurons inside. “How these particular vertebrates have kept this ability to regenerate while others have lost or blocked it fascinated me,” says Tanaka, who describes the axolotl as “an interesting and important organism for studies on the evolution of vertebrate traits.” Her lab has analyzed signaling pathways that control regeneration, such as “proteins that tell a regenerating cell whether it should form an upper arm or lower arm cells.” In a paper last year in Development, her group shed light on how the axolotl’s neural progenitor cells are activated to help regenerate a segment of spinal cord….

Among the stem cell scientists who use axolotls in their research is Andrew Johnson of the Institute of Genetics at the University of Nottingham in the U.K., who studies the production of primordial germ cells (PGCs) in the salamander’s embryos. “Axolotls are significant in that they share a mechanism that has been conserved during the evolution of mammals, in which PGCs are produced from pluripotent stem cells,” Johnson says. His group is investigating how such stem cells ignore signals that typically trigger somatic cells to differentiate.

But this is the habitat the axolotl is trying to survive in:

Leaning over the Traginera flatboat’s edge, Luis Zambrano surveys a canal floating with plastic bottles, Styrofoam cups, and a leafy carpet of invasive lilies. African tilapia fish ripple the brown water’s surface and a Chinese carp lurks underneath, but Zambrano sees no signs of his elusive goal: the axolotl salamander.

“We’ve spotted only a few in 6 months,” says Zambrano, a freshwater ecologist at the National Autonomous University of Mexico (UNAM) who is trying to count and preserve the feathery-gilled, 33-centimeter-long salamanders in their only natural habitat, the Xochimilco network of polluted canals and small lakes in and around Mexico City, the world’s third largest metropolitan area.

Five hundred years ago, axolotls–named for an Aztec god who transformed into a water animal to avoid being sacrificed–were common in the lakes around the Aztec capital. But as the wetlands receded, so did the axolotls, to the point that Zambrano now estimates a population density of only 100 per square kilometer of wetland, compared with estimates 10 times higher in 2004 and another six times higher than that in the 1980s. The species, Ambystoma mexicanum, is now classified as critically endangered by the International Union for Conservation of Nature.

Another threat faced by the axotol are introduced tilapia. While a small reintroduction/sanctuary program has started, it’s unclear if it will be successful. Even though there are many laboratory colonies, wild populations are critical for research:

Neurobiologist Alejandro Sanchez Alvarado, who studies the molecular basis of regeneration at the University of Utah School of Medicine in Salt Lake City, says losing the wild axolotls would be a tragedy. “Wild-type populations provide us with a window, a record of how biological traits evolve genetically,” he says. “Who is to say that unlocking the evolutionary mystery shrouding regenerative capacities in vertebrates will not come from studying wild axolotl gene pools?”

Comments

  1. #1 James F
    December 6, 2008

    From MAD magazine #43, 1958:

    I Wandered Lonely as a Clod

    I wandered lonely as a clod,
    Just picking up old rags and bottles,
    When onward on my way I plod,
    I saw a host of axolotls;
    Beside the lake, beneath the trees,
    A sight to make a man’s blood freeze.

    Some had handles, some were plain;
    They came in blue, red pink, and green.
    A few were orange in the main;
    The damndest sight I’ve ever seen.
    The females gave a sprightly glance;
    The male ones all wore knee-length pants.

    Now oft, when on the couch I lie,
    The doctor asks me what I see.
    They flash upon my inward eye
    And make me laugh in fiendish glee.
    I find my solace then in bottles,
    And I forget them axolotls.

  2. #2 genghisprawn
    December 6, 2008

    “I used to love axolotl tamales.” — Roberto Altamira, 32.

    Don’t forget the neoteny and forced metamorphosis through iodine injection!

  3. #3 Coturnix
    December 6, 2008

    The Axolotl and the Ammocoete

    by Walter Garstang

    from “Larval Forms, and other Zoological verses”, 1966

    Ambystoma’s a giant newt who rears in swampy waters,
    as other newts are wont to do, a lot of fishy daughters:
    These Axolotls, having gills, pursue a life aquatic,
    But, when they should transform to newts, are naughty and erratic.

    They change upon compulsion, if the water grows too foul,
    for then they have to use their lungs, and go ashore to prowl:
    but when a lake’s attractive, nicely aired, and full of food,
    they cling to youth perpetual, and rear a tadpole brood.

    And newts Perrenibranchiate have gone from bad to worse:
    They think aquatic life is bliss, terrestrial a curse.
    They do not even contemplate a change to suit the weather,
    But live as tadpoles, breed as tadpoles, tadpoles all together!

    Now look at Ammocoetes there, reclining in the mud,
    Preparing thyroid-extract to secure his tiny food:
    If just a touch of sunshine more should make his gonads grow,
    The lancelet’s claims to ancestry would get a nasty blow!

  4. #4 becca
    December 6, 2008

    Such a cute little amphibian!
    Way better than xenopus
    *ducks*

  5. #5 Coturnix
    December 6, 2008

    The Axolotl
    McCord, David (1897-)

    The axolotl
    Looks a littl
    Like the ozelotl,
    Itl

    “Drink a greatl
    More than whatl
    Fill the fatl
    Whiskey bottl.

    “The food it eatsl
    Be no morsl:
    Only meatsl
    Drive its dorsl.

    “Such an awfl
    Fish to kettl!”
    “You said a mawfl
    Pop’epetl!”

  6. #6 oyun
    December 7, 2008

    Thanks you really perfect one writing.I m always follow you.

  7. #7 Chad
    December 8, 2008

    I worked with a lot of axolotls as an undergrad and must say that they somehow got a bum rap simply for looking goofy. I’m glad I don’t work with them anymore simply because working with aquatic animals is a pain in the ass, but it was good while it lasted.

    Little known fact: axolotls are fucking vicious. It was not uncommon for me to find axolotls with between one and four limbs bitten off by tankmates.

  8. #8 Kristin
    December 8, 2008

    Am I the only one whose first thought on seeing the word “axolotls” was of Dune?

  9. #9 estetik
    December 9, 2008

    he damndest sight I’ve ever seen.
    The females gave a sprightly glance;
    The male ones all wore knee-length pants.

  10. #10 komik fıkralar
    April 7, 2009

    “The food it eatsl
    Be no morsl:
    Only meatsl
    Drive its dorsl.

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