Fish antifreeze proteins give clues to the evolution of novel genes – oceanbites

Rives, N., Lamba, V., Cheng, C. C., & Zhuang, X. (2024). Diverse origins of near-identical antifreeze proteins in unrelated fish lineages present insights into evolutionary mechanisms of new gene beginning and protein sequence convergence. Molecular Biology and Evolution, 41(9), msae182. 

Freezing fish

Temperatures in the frigid polar oceans can attain under zero as a result of the salt in seawater lowers the freezing level (to about -2 °C or 28 °F). This raises a main query: how come fish don’t freeze? The reply lies with particular molecular adaptation: antifreeze proteins.

Antifreeze proteins work by attaching to microscopic ice crystals in the physique, stopping the crystals from growing. Many completely different teams of fish have advanced antifreeze proteins independently, making them an instance of “convergent evolution.” Convergent evolution signifies that the identical trait evolves more than as soon as in numerous, unrelated teams of organisms—for instance, the wings of birds, bugs, and bats. Convergent traits are helpful to evolutionary biologists as a result of we are able to see, repeatedly, how evolution makes new traits.

Fish antifreeze proteins are a great system to examine the origins of new genes as a result of they’ve advanced convergently many occasions and have a clearly-defined molecular operate. In this examine, scientists examine an antifreeze protein, AFP1, in three lineages of polar fish; flounder, sculpin, and cunner. By trying intently at the fishes’ genomes, they decide the origins of the AFP1 gene in every species, and describe how completely different genomes advanced to produce comparable protein sequences.

Where do new genes come from?

In order for an organism to adapt to its surroundings, it wants genetic materials that may purchase new, adaptive features. Organisms can purchase new genes in many alternative methods, together with modifications and duplications of current genes. The duplicated gene is free to evolve new features, whereas the previous gene can keep performing its authentic operate. Genes may also generally come up fully “de novo”, or anew, from different elements of the genome. However, we nonetheless don’t totally perceive the mechanisms as a result of the evolution of new genes.

A primer on evolution

Gene evolution is a little bit sophisticated, and there are a few ideas that we need to focus on so as to perceive how it really works. First, DNA can both be “coding” or “non-coding.” Coding DNA is the half of the genome that makes proteins-–the sequence of DNA encodes the construction of the protein, and the proteins go on to carry out organic features. Non-coding DNA, on the different hand, can do all kinds of different issues, together with regulating the place, when, and how protein-coding genes are expressed. Non-coding DNA is variety of like the areas and punctuation marks that help us learn paragraphs, whereas the coding DNA is simply the letters themselves.

A gene is a chunk of DNA that makes one protein, and it wants two elements so as to work: the protein-coding half, and the regulatory, non-coding half.

The different ideas we need to perceive are natural choice and mutation. Mutations come up all the time, randomly, each time an organism reproduces. Very hardly ever, mutations may be advantageous, however most of the time they’re dangerous or just impartial. Natural choice removes dangerous mutations, which is why genes preserve their sequences over long durations of time. If you had no choice, random mutations would accumulate and the gene would ultimately decay. In different phrases, genes are maintained over time by natural choice as long as they supply an benefit for the organism to survive and reproduce.

Now, back to the fish! 

The three fish have AFP1 genes are practically equivalent in sequence, as a result of they carry out the identical operate. However, they arose independently. How did three genes independently purchase nearly the identical protein sequence?

To be taught more about the origins of AFP1 genes, the researchers examined the elements of the genome that gave rise to every gene and reconstructed their evolutionary histories. They discovered that the genes arose from completely different precursor genes that every carried out completely different features in the three species. These genes had all duplicated and decayed, and had been then re-purposed into the new antifreeze proteins. Importantly, the protein-coding elements of the genes had been completely modified, however the non-coding regulatory elements of the genes had been intact.

Putting this all collectively, the scientists define the following steps to producing a new antifreeze protein.

You begin with an authentic gene performing another operate. First, that gene duplicates due to a mutation. After a gene duplicates, the second copy is redundant—the organism doesn’t need two copies of the gene, so the second copy is free to accumulate random mutations and begins to degenerate. Critically, as a result of the non-coding regulatory DNA remains to be round, the degenerating gene remains to be lively. Then, the degenerated gene copy, by likelihood, provides the fish a survival benefit in cold temperatures as a result of its construction has ice-binding talents. Finally, choice acts to improve and preserve that new operate.

Animals have many beautiful variations to their surroundings, and this analysis reveals how finding out these variations can help us find out about elementary organic questions! In this case, we gained a clearer image of how new genes come up out of the fragments of previous genes.