The remnants of some ancient viruses survive in the human DNA, and without them we could not form or function correctly.
Photo DNA change: Shutterstock
It seems that a gene called LTR5HS activates another, which influences the growth of the embryo and the proliferation of stem cells. LTR5HS is the newest known viral gene group, discovered as essential in the process of forming the embryo. The evolution has taken some bizarre twins, and some of them seem directly detached from a cartoon. Proof-Human DNA has become what it is due to viruses, writes populationchanics.com.
About 9% of our genetic material is believed to represent the remains of ancient viruses that have taken control about 5 million years ago (which, in evolutionary terms, is relatively recent).
While some of these remnants seem to be involved in the onset of diseases, others have become such an integral part of us that people could not even develop in the uterus without them. Many of these sequences are unique for homo sapiens.
LTR5HS – an essential group of viral genes
LTR5HS is the newest group of such known viral genes. Acquired as a result of ancient viral infections, these genes appeared in the ancestors of the people and the great monkeys, when they separated from the small monkeys.
These human endogenous retroviruses (HERV) have been considered long as a residual DNA, without significant role. However, in recent years, it has been discovered that they represent sequences from retroviruses – viruses whose genomic material is made up of RNA. When a cell is infected by a retrovirus, an enzyme converts that RNA into DNA, which then becomes incorporated into the genome of the cell.
Research of biologist Raquel Fuyo
Biologist Raquel Fuyo, from Stanford University, wanted to find out how relatively recent genes from retroviruses can provide essential functions in terms of development. She and her research team investigated an early stage of embryonic development from stem cells, called blastoid.
This blastoid was meant to behave like a blastocyst, the growth stage that precedes implantation in the uterine mucosa. Fuyo disabled LTR5Hs and found that blastoid formation had dysfunction in their absence – the median tissue layer, called Epiblast, could not be properly formed.
“We have shown that Hervk LTR5HS activity is necessary for the formation of blastoid and for the identity of cellular lines”, she said in a recently published study in Nature magazine. “Ltr5Hs elements function as potentiators, and as a result, ltr5HS repression severely affects the transcriptoma of the blastoid epiblast.”
The crucial role of the developing epiblast
Epiblast is essential in development, because it will later become the embryo itself. Also, the epiblast gives rise to the early phases of the placenta (trivetoderm) and the vitelline sac (hypoblast). It has been discovered that hervs are expressed intensely in both structures, and deactivation of LTR5HS affects the number of cells in hypoblast and trivectoderm.
In the formation of epiblast, this deactivation prevents LTR5HS from stimulating the expression of the gene ZNF729, which activates or inhibits other genes involved in the growth of the embryo. This process leads to the proliferation of stem cells which will subsequently differentiate into specific tissues.
The evolution of the gene ZnF729
Fuyo believes that ZNF729 has expanded during the evolution of primates. This gene is linked to hundreds of other important genes and regulates them, increasing in time the activity of the genes that maintain the basic cell functions – thus offering cells that express an advantage in proliferation.
ZNF729 could have replaced an older mechanism that once controlled the cell proliferation, becoming essential for the correct development of the pre -implantation phases of the embryo.
“These observations”said the researchers, “suggests that the evolutionary remodeling of the genetic regulation networks can lead not only to the specific innovations, but also to the creation of new addictions and to a character essential to relatively recent elements and genes.”
