About sixty percent of the genomes of human beings and bananas are similar. So does that mean we are bananas? Well, no - only in a figurative sense. The regulation of gene expression is essential to the definition of cells, tissues, and organisms. While we may have far more in common with organisms like chimpanzees, the when and where of gene expression has an essential and undeniable effect on the ultimate definition of an organism.
Humans have so much in common, genetically speaking, with other organisms in part because so much life in the world is derived from a common ancestor. Animals with a front, back, top, and bottom, have a body plan with bilateral symmetry. This originated about seven hundred million years ago with the first bilatarian creature. This basic body plan would eventually be inherited by many other life forms, including humans.
The world's first bilatarian was probably an ancient marine animal that lived on the seafloor. It would give rise to all vertebrates, including birds, mammals, and reptiles, and invertebrates like insects, worms, mollusks, arthropods, and other animals.
Scientists have now shown that about 7,000 gene groups can be traced back to this last common ancestor of bilatarians. This work investigated the genomes of twenty bilatarians including centipedes, mayflies, sharks, octopuses, and humans. The findings have been reported in Nature Ecology & Evolution.
About half of these ancient genes have been used by different animals for very different purposes in various parts of the body, notably in the brain and reproductive organs. This work has indicated that some errors in a kind of copy-and-paste genetic swapping method has given rise to many different characteristics in vertebrate evolution.
Some genes that are specifically used in certain tissues also emerged during events in which the entire genome was duplicated. With duplicate copies of genes, animals were free to use one copy for basic, essential processes, while the other copy could be modified for innovation. These events can be seen at varying scales throughout the evolutionary development of bilatarians.
"Our genes are like a vast library of recipes that can be cooked up differently to create or change tissues and organs. Imagine you end up with two copies of a recipe for paella by accident. You can keep and enjoy the original recipe while evolution tweaks the extra copy so that it makes risotto instead," explained study co-author Federica Mantica, a researcher at the Centre for Genomic Regulation (CRG) in Barcelona.
"Now imagine the entire recipe book is copied twice, and the possibilities it opens for evolution. The legacy of these events, which took place hundreds of millions of years ago, lives on in most complex animals today."
Ancestral genes like TESMIN and tomb came from the same common ancestor, but they have special functions in the testes of vertebrates and insects, for example. Disruptions in the genes can interfere with sperm production and fertility in mice and fruit flies.
Other ancestral genes help promote the growth of complex nervous systems. There are gees in vertebrates that are essential for the production of myelin, which insulates neurons and enable the rapid propagation of signals in the nervous system.
The use of different genes depends greatly on context, and when tissues activate new genes, novel traits or abilities can arise, and boost evolution.
"Our work makes us rethink the roles and functions that genes play. It shows us that genes that are crucial for survival and have been preserved through millions of years can also very easily acquire new functions in evolution," added study co-author and Professor Manuel Irimia of CRG. "It reflects evolution's balancing act between preserving vital roles and exploring new paths."
Sources: Center for Genomic Regulation, Nature Ecology & Evolution