Vision is a remarkable sense that allows us to perceive the world around us.
But have you ever wondered where the genes for vision came from? It may amaze you that some of the genes responsible for vision in vertebrates originated in bacteria.
According to a recent study published in the Proceedings of the National Academy of Sciences
(PNAS), the key gene involved in vertebrate vision has been traced back to bacteria. The idea that
genes could be transferred between different organisms is not new.
In fact, scientists have known for some time that bacteria can exchange genetic material with each
other through a process called horizontal gene transfer.
However, it was not until recently that researchers discovered that horizontal gene transfer could also occur between bacteria and animals.
Back in 2001, when the human genome was first sequenced, the experts thought it contained nearly
200 bacteria-derived genes however, the microbial origins of plenty did not hold up.
This process involves the transfer of genetic material between different bacteria cells and can result
in the acquisition of new genes that confer beneficial traits such as antibiotic resistance.
A retinal biologist at the University of Sydney’s Save Sight Institute, who was not involved in
the work, said: “Their findings demonstrate how complex structures like the vertebrate eye can
evolve, not only by modifying existing genetic material but also by acquiring and integrating foreign
genes”.
In particular, they found that some of the genes responsible for vision in vertebrates have a bacterial
origin. “It’s incredible”, he added.
The study suggests that some 500 million years ago, bacteria likely transferred the gene to the
ancestor of all vertebrates.
How did this happen?
The genes that seem to have appeared first in vertebrates do not link back to earlier animals, which
rules out the possibility of having a predecessor in earlier animals.
Its absence in invertebrates and in any other complex cells like plants, yeast, etc. Therefore, it increases its chances of having a close resemblance to bacteria, especially if they had modern microbes.
A gene called IRBP – interphotoreceptor retinoid-binding protein – is already known to facilitate the
physical separation between light sensing and retinoid regeneration. It has the most similar protein
sequence to a bacterial protein called peptidase. A key element is known to break down proteins
and recycle them.
“A growing list of eukaryotic functions owe their origins to bacterial and viral genes, including
components of antiviral and antibacterial immunity, metabolic functions, adaptation to
environmental stress, and now an essential component of vertebrate vision”, the experts wrote in
their study.
In addition, a mutated version of the gene can lead to several retinal diseases in humans. For
instance, retinal dystrophy – a group of degenerative disorders of the retina that can cause color
blindness and complete blindness under progressive conditions.
Due to the advances in eye arrangements in animals over the course of 500 million years, scientists
do not have a complete picture of exactly how the vision in vertebrates has evolved.
According to a 2008 study entitled ‘The Origin of the Vertebrate Eye’, hard bodies were either not
preserved or very poorly represented in fossils before the evolution of skeletons.
Furthermore, in the face of advancements concerning eye arrangements, prior ones are very unlikely
to have survived for hundreds of millions of years. Connecting the missing dots, the researchers
reconstruct the origin of IBRP.
Whether IBRP acquisition from bacteria played a crucial role in the evolution of vertebrate vision or
was a mere ‘historical accident’, remains a contested issue among researchers.
Nevertheless, the study revealed a possible pathway through which something as complex as the
vertebrate eye must have evolved.