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| Image by Gerd Altmann from Pixabay |
Over 4 million years ago Ardipithecus ramidus, the earliest ancestor of Homo sapiens was the first to show Bipedalism (the ability to walk on two legs). Bipedalism was the result of Human evolution.
Evolution
Evolution
is nothing but a gradual change in the characteristics of organisms in a
changing environment. Evolution may be due to mutation, gene flow, genetic
drift, and natural selection.
The
development of a larger brain, the ability to live at higher altitudes where
oxygen concentration is low, the ability to resist contagious diseases,
bipedalism, and so on were the result of Evolution.
Over 500
million years ago the ancestors of Vertebrates lacked Myelin Sheath and it
suddenly appeared among the vertebrates without any trace of evolution. Recently,
Researchers found that the presence of Myelin sheath was not due to evolution
and it was due to the infection of the virus.
The Solution to the Myelin Mystery
The Myelin
sheath which covers the nerve fibers is made up of protein and fatty substances.
Schwann cells produce myelin which covers the nerve fibers present in the body
and Oligodendrocytes produce myelin which covers the glial cells present in the
Brain. Though the source of myelin of nerve fibers present in the body and
brain may be different but their function is the same. Nerve fibers with myelin
sheath conduct impulses faster than that of nerve fibers that lack myelin
sheath. Formation of the myelin sheath around the nerve fibers is unique to
Vertebrates. But how does this happen all sudden to the vertebrates, if it is
not due to evolution what might be the possible reason? A new study in CELL Journal
provides an answer to this question.
You all are
aware of HIV(Human Immunodeficiency Virus) which is a retrovirus. Retrovirus is
a type of virus that injects its RNA into the host cell. This RNA gets
converted to DNA by an enzyme called Reverse transcriptase. This viral DNA gets
integrated into the host DNA. Whenever the host DNA replicates, the integrated
viral DNA also replicates. Once the replication completes, transcription and
translation occur which ultimately produces viral proteins. Such virus that corrupts
the human genome causes dreadful infections and cancers but sometimes it can be
beneficial.
How could that be beneficial?
Sometimes
the viral fragment that is going to integrate with the host DNA might be
mutated. This mutant viral fragment integrated with the host DNA passes on to
generation and they no longer produce viral proteins. Nearly 40% of the human
genome are remnants of viral infections. Now you might get an idea of how nerve
fibers of vertebrates could have got the myelin sheath. Researchers coined the
term RetroMyelin for the fragment of viral DNA which is responsible for
Myelin production.
Myelin
formation failed when researchers blocked Retromyelin within the mouse
cells in culture. The protein which is responsible for the production of myelin
is known as Maltose Binding Protein(MBP). Retromyelin binds to SOX10
which is a protein, a transcription factor. SOX10 plays a crucial role in the development
and differentiation of cells called Schwann cells and Oligodendrocytes by
producing a larger amount of MBP. Retromyelin regulates the function of
SOX10, which indirectly leads to the formation of Myelin by producing MBP. So, this
explains that the blocking of Retromyelin within the mouse cells led to the
failure of myelin formation.
Conclusion
In short,
Researchers found that over 500 million years ago, Retrovirus injected the Retromyelin(A
specific genetic sequence injected into the genome of vertebrates) that
regulates a protein, a transcription factor called SOX10. This SOX10 regulates
the formation of MBP.
MBP present in the Schwann cells and Oligodendrocytes leads to the formation of Myelin sheath.