Tracing the evolution of genes sheds light on origins of life

Looking at how genes function across different species is helping to answer questions about human origins as well as how we view life on Earth.

Dr Davide Pisani is integrating genomic data with palaeontological data to answer fundamental questions such as when vision first originated in animals and what was the first chemical smelled.

Pisani, Reader in Phylogenomics, considers the work in his research program to be the phylogenomic approach to ‘think global, act local’.  In order to answer broad questions about the origins of animals and how they process information from their environment, Pisani uses complex computational analyses to trace the ancestry of specific genes.

His recent work has traced the origins of opsins, which are the light-sensitive proteins key to vision. 

"What we found was that opsins originated after the sponges split from the common ancestor to all other animals. This is particularly relevant as it shows that vision originated only once in animals and as a consequence, reveals how and when vision evolved in humans."

More than 711 million years ago, a common ancestor to humans as well as placozoans, which are tiny amoeboid-like creatures that inhabit the ocean floor, duplicated a gene and one of the copies acquired the ability to detect light. Placozoans possess this basic opsin gene, but don’t have the subsequent mutation that makes the opsin protein light-sensitive. Human ancestors, however, were on the evolutionary branch that did undergo duplication and mutation events around 700 million years ago that led to the three different light-sensitive opsin proteins that exist in visual systems today.

"What we want to do now is link this information to the origins of chemoreception. Look at when chemoreception originated, what the first molecule ‘smelled’ was, and tie together the different systems used to perceive the environment."

Pisani has also used his approach to look at the genetic relatedness of many living organisms, including bacteria in order to better understand the origins of the eukaryotic cell – a topic that has been debated for decades.  Eukaryotic cells have complex compartmentalised structures and all complex organisms, including plants, animals and fungi, are eukaryotes.

One hypothesis is that eukaryotes evolved from a nucleated ancestor and subsequently underwent compartmentalisation to develop various organelles. However, Pisani’s research supports the more current hypothesis that suggests eukaryotes are the result of the fusion of organisms from two different domains - eubacteria and archaebacteria – either through some sort of physical fusion or endosymbiosis.

“Eukaryotes are a genetic mosaic of these two genomes,” said Pisani, “which supports a symbiotic hypothesis.  From this perspective, all eukaryotes, including ourselves, are effectively hybrids. This tells us a lot about the nature of life and offers a new way of looking at organisms.”

In terms of the impact of his research, Pisani admits that he’s not going to find a cure for cancer or induce political change. However, his research could have profound implications for our understanding of life’s origins.  

“In a sense, the impact of our research is philosophical,” said Pisani. “We try to answer questions that impact how we perceive the world and to some extent how humanity perceives itself – to have a better understanding of what we are and where we came from.”

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