Cells within the salamander's tissues called fibroblasts also congregate beneath that epidermal covering. Fibroblasts are undifferentiated, which means that they're free to become multiple types of cells, depending on which body part needs replacing. After that initial phase, the blastema develops from the mass of fibroblasts; the blastema will eventually become the replacement body part.
Researchers recently discovered that the expression of a protein called nAG kick-starts blastema growth [source: Kumar et al ]. The blastema is sort of like a mass of human stem cells in that it has the potential to grow into various limbs, organs and tissues. But how does the salamander's body know what needs replacing? The genetic coding in the blastema contains a positional memory about the location and type of missing body part.
That data is stored in the Hox genes in the fibroblast cells [source: Muneoka, Han and Gardiner]. While this is happening, capillaries and blood vessels are regenerating into the blastema. As the blastema cells divide and multiply, the resulting mass becomes a bud of undifferentiated cells. In order for that mound to become a full-fledged limb, tail or other body part, it must receive stimulation from nerves [source: Kumar et al ]. However, when salamanders drop their tails, they lose not only flesh but also nerves.
That means that nerve axon regeneration is happening at the wound site in tandem with tissue, bone and muscle regeneration. From there, the cells differentiate and create the appropriate body part.
As part of that positional memory in the fibroblast cells, the blastema knows to grow in the proper sequence to avoid defective regeneration. For example, if a salamander loses a foot at its ankle, the blastema will develop outward to form a foot instead of an entire leg.
With the salamander as the blueprint, scientists hope to someday engineer blastemas from human cells. Until then, our amphibian friends are still the reigning regenerators of the animal kingdom. From Quanta Magazine find original story here. Up close, axolotls are just on the cute side of alien. They have fleshy pink bodies and guileless, wall-eyed faces.
Unlike most salamanders, which metamorphose into land-dwellers as they grow up, axolotls usually keep their youthful aquatic form for their whole lives. They wear their gills on the outside, a set of three feathery horns on each side of the head. One of the animals in view is missing a limb that was amputated 11 days earlier. Salamanders are champions at regenerating lost body parts. A flatworm called a planarian can grow back its entire body from a speck of tissue, but it is a very small, simple creature.
Zebra fish can regrow their tails throughout their lives. Humans, along with other mammals, can regenerate lost limb buds as embryos. As young children, we can regrow our fingertips; mice can still do this as adults. But salamanders stand out as the only vertebrates that can replace complex body parts that are lost at any age, which is why researchers seeking answers about regeneration have so often turned to them.
While researchers studying animals like mice and flies progressed into the genomic age, however, those working on axolotls were left behind. One obstacle was that axolotls live longer and mature more slowly than most lab animals, which makes them cumbersome subjects for genetics experiments.
Then a European research team overcame the hurdles and finally published a full genetic sequence for the laboratory axolotl earlier this year. That accomplishment could change everything. The next showed a triangle sitting atop that table; the tail was somehow regrowing. These drawings by the 18th-century Italian cleric Lazzaro Spallanzani are the first known representations of regeneration in salamanders.
In the second, a mound of unspecialized cells called a blastema has formed atop the stump as a precursor to regrowth. Details signifying the development of a spinal cord in the regenerating tail are visible in the third.
Spallanzani had been experimenting on salamanders, tadpoles, snails and earthworms and found that they could regenerate lost body parts.
He shared that discovery and his drawings in a letter to the naturalist Charles Bonnet in Two years later, Spallanzani published his observations more widely in a brief collection of essays on reproduction and regeneration. Researchers who care for the animals generally agree that axolotls are inquisitive and alert to the presence of humans, who might be bringing food, although in general the axolotls are not too bright.
They are extremely inbred, after all. Most wild axolotls are a mottled mud color rather than pale pink, but the lab animals are not albinos—true albino axolotls are yellowish, with golden eyes rather than black. Since those animals were removed, their native waterways around Mexico City have been polluted, invaded by introduced species that altered the ecosystem and dramatically depleted by urbanization.
Axolotls are also a traditional food for locals. But the laboratory population has thrived. In , some of those European axolotls came back to North America and eventually became a collection at Indiana University under the direction of the biologist George Malacinski. When he retired in , the University of Kentucky inherited his colony of or so animals. Although the drive lasted only about three hours, the stress made some of the salamanders metamorphose.
Today the stock center aims to keep to 1, adults at a time. Pedigree records going back to help the center maintain the remaining genetic diversity in the inbred group. It ships axolotl embryos, larvae and adults to labs and classrooms around the world. But although these labs have learned much from the axolotl, none of them could fully sequence its genome. It has 32 billion base pairs, making it about 10 times longer than the human genome.
Despite that, axolotls and humans seem to have a similar number of genes, said Elly Tanaka , a biologist at the Research Institute of Molecular Pathology in Vienna. These genes are like islands in oceans of highly repetitive sequence.
That overabundance of repetitive DNA has been the problem. Yet even before the axolotl genome was mapped, scientists were using other tools to begin to understand regeneration. We were facing shelves lined with dozens of axolotl tanks; the lab keeps about or animals.
Wiping out these cells permanently prevented regeneration and led to tissue scarring. The findings hint at possible strategies for tissue repair in humans. Test Your Body Smarts ]. In mammals, macrophage cells play an important role in the immune system response to injury, arriving at a wound within two to four days. There, they engulf and digest pathogens, or infectious particles, and generate both inflammatory and anti-inflammatory signals for healing. Now, Godwin and his colleagues have shown that macrophages are essential for salamanders' superherolike ability to sprout new limbs.
The researchers studied the biochemical processes that occurred in salamanders at the site of a limb amputation. They then wiped out some or all of the macrophage cells to determine whether these cells were essential for regrowing the limbs. Signals of inflammation were detected at the wound sites within one day of the amputations.
0コメント