We have 3 stories to cover today. In the first we will explore how the remarkable axolotl
could hold the key to understanding how humans could regrow organs and limbs. In the second
we examine a new study that reveals the human chromosomes weigh 20 times heavier than the
DNA they contain and lastly we will look at the strange occurrence of the Z genome discovered
in some virus that may point to an extraterrestrial origin.
We know that in the wild there are certain animals that have the remarkable ability to
regenerate whole limbs when they lose one. It was assumed that this ability was something
very specific to that species. It somehow managed to develop this as a strategy to help
it survive. When we get an injury and the skin is cut deeply enough our first thought
is to stop an infection and clean the wound. If the cut is deep enough we end up with scar
tissue. In a remarkable new study, scientists were studying the role that scars play in
the healing process and discovered that this may actually be preventing an even more remarkable
process of healing!
In a new paper, researchers led by James Godwin of MDI Biological Laboratory were trying to
figure out the differences between mammals and a very special species of salamander called
the axolotl.
Axolotls are a severely endangered species in the wild. What makes them a very unique
creature is their ability to regenerate a wide range of body parts. It is common knowledge
that salamanders, lizards and other amphibians are capable of regenerating their tails. Axolotls
take this to a whole new level. Not only can they regenerate external parts like a tail,
leg or skin. They are also capable of regenerating internal organs like new lungs, ovaries, spinal
cords and even a fresh brain or heart if needed.
The scientist studied what happens to wounds on a molecular level in both mice and axolotls.
After an injury special immunes cells called macrophages trigger a response. These appear
to be the critical link that allows an animal to regrow body parts. In the experiments,
the scientists were able to show that when the axolotl had too few of these immune cells
react to an injury, the missing body part could not be regrown and a scar would appear
instead.
In both mice and humans, macrophages trigger scarring rather than regeneration, but their
research suggests that it may be possible to change this. James Godwin goes on to state
the following:
“Our research shows that humans have an untapped potential for regeneration. If we
can solve the problem of scar formation, we may be able to unlock our latent regenerative
potential. Axolotls don’t scar, which is what allows regeneration to take place. But
once a scar has formed, it’s game over in terms of regeneration. If we could prevent
scarring in humans, we could enhance the quality of life for so many people.”
Through their work, they were able to identify that a signal from a specific protein seemed
to be responsible for the specific response of the macrophages. They also discovered that
the responses in axolotls and mice were very different. This suggests that it might be
possible to modify the signalling to be able to trigger the regeneration in mice tissue
and hence eventually in humans.
In a somewhat related article scientists have been struggling to explain an excess of mass
lurking inside the human chromosomes. Maybe this is where all the dark matter is! Human
genomes weigh about 20 times heavier than the DNA they contain. They created a 3D model
of the chromosomes by shooting them with an extremely powerful X-ray beam. This allowed
them to calculate the precise number of electrons in each chromosome, which was then used to
estimate the chromosomes’ total mass.
The results surprised them. Each chromosome was 20 times heavier than the DNA contained
inside them. Human cells contain 23 pairs of chromosomes. Each chromosome is one DNA
molecule and a whole collection of proteins that perform various functions. The mass of
the DNA molecules was first discovered by the Human Genome Project. These extra proteins
cannot account for the 20 fold increase in mass in the chromosomes. So far there is no
good explanation.
In a different piece of research, scientist have discovered that some bacteria-invading
viruses carry around DNA with a different letter to that of all other known DNA. This
difference has been known about for some time but it was thought to be very rare. This new
study however shows that it is much more widespread than previously thought.
DNA is almost always constructed using the same four-letter alphabet of chemical compounds
known as nucleotides: Guanine (G), Cytosine (S), Thymine (T) and Adenine (A). A DNA strand
in composed of two strands of these chemicals which are tied together in a double helix.
The alphabet that is used is the same for a plant as it is for a human, the instructions
are just different. RNA uses the same alphabet but exchanges Thymine for Uracil (U).
In 1977 Russian scientist discovered that a virus which invades cyanobacteria had substituted
all of its As for the chemical 2-aminoadenine (Z). This changes its alphabet from ATCG to
ZTCG. In the late 1980’s they discovered that the use of the Z nucleotide meant that
it had some clear advantages: it was more stable at higher temperatures
It helped one strand of DNA bind more accurately to the second strang of DNA after replication
Z-DNA could resist certain proteins present in bacteria that could normally destroy viral
DNA.
The phages carrying this Z-genome could be considered as a different form of life but
it is difficult to know the exact origin. When they analyzed sequences of phages with
the Z-genome and compared them to other organisms. They discovered that the z-genomes are actually
more widespread than previously thought. They discovered it in more than 200 different types
of bacteriophages.
The scientists identified two different proteins which are involved in the making of this Z
nucleotide. When they analysed the evolutionary history of these proteins they discovered
that it is related to a protein found in some single-celled organisms. This distant evolutionary
connection raises the question of whether these proteins first arose in bacteria and
were eventually adapted by viruses.
To further add to this mystery a meteorite that fell in the Antarctic in 1969 was analysed
in 2011 and they discovered the Z-nucleotide alongside some standard and nonstandard nucleotides
likely of extraterrestrial origin. This raises the question of whether the Z-nucleotide plays
an important role in allowing early lifeforms to survive in more harsh environments.