The evolution of the human eye For a long time One of the most challenging mysteries in biology, the sequence of steps required to transform a primitive photosensitivity into a complex photographic system is arguing.
New research suggests that some components of vertebrate vision may not have formed gradually because their genes are passed down along family lines, but were “stolen” from entirely different branches of life.
“At least one innovation that led to the present structure of vertebrate eyes did not come from the gradual ‘patching over’ of genes found in other animals, but came from the introduction of new DNA from bacteria by horizontal gene transfer,” Explain Molecular biologist Matt Dougherty of the University of California, San Diego (UCSD) on Twitter.
Horizontal gene transfer It describes the process of transferring genetic material between different types of organisms, such as gene-swap viruses or sticky bacteria.
One of the main features that distinguishes our fine-focus, camera-like eyes from those of invertebrates is the separation of light-sensing tissues from cells responsible for recycling their light-reacting molecules.
It’s worth noting that invertebrates also have amazing eyes so they’ve obviously evolved different solutions for visual acuity. We only rely on IRBP and they don’t, which means that acquiring this bacterial gene sets us on an evolutionary path that makes our eyes what they are. 7/
– Matt Daugherty (@Daugherty_Lab) April 10, 2023
This relies on mechanisms to actually move molecules, called retinoids, between different cells. Highly conserved retinoid receptor-binding protein (IRBP) It does the transfer, and according to this new research, it originated from a bacterial gene that suddenly appeared in vertebrate-like eyes more than 500 million years ago.
Not only is IRBP absent in invertebrates, it’s not found in any other complex cell either, from trees to amoeba to yeast. The only record we have of the gene A sequence similar to the one encoding IRBP is from bacteria.
By analyzing more than 900 genomes, MIT molecular biology graduate student Chinmay Kalluraya and colleagues were able to determine the gene’s appearance in vertebrate lineages. This coincided with the appearance of vertebrate-like eyes more than 500 million years ago.
It seems that the ancestors of all backcrossed animals stole the original gene from bacteria, and over many generations of natural selection, Its codon replication and function is formed to transport retinoids.
Although it plays only one small role in vertebrate vision, the fact that novel components can slip between vastly different parts of the biosphere presents new possibilities for explaining many complex biological processes. Another example of this is a protein necessary for the formation of the placenta in mammals called syncytin. gene for this protein It originated in retroviruses.
“Unlike the evolution of existing genes, or so-called modification, the acquisition of foreign genetic material has the potential to permeate the evolution of eukaryotes by providing immediate functional novelty,” Explain in their paper.
As more genomes are sequenced, the researchers believe we will find more examples of horizontal gene transfer in our evolutionary history.
“DNA from microbes (including viruses) has shaped the evolution of animals in strange and surprising ways.” He says Dougherty.
This research has been published in PNAS.
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