You May Be Stuck With Your Same Old Genome, but Corals Aren’t
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Some corals live to be hundreds and, even thousands of years old. They were born with genes that were successful back in their parent’s generation, so how can these old corals still be successful now? Especially in a changing climate? It’s possible that the generation and the filtering of mutations that occur in different parts of a big coral act as a proving ground for adaptive genetics for the future. The new study from Stanford, Hopkins Marine Station and the California Academy of Sciences shows a novel way that some very ancient animals might be surviving.
You got your entire set of genes– good or bad - from your parents, and those are the only genes you will have for your entire life. Those genes are also the only ones you will pass along to your children. Of course, there are a few exceptions - like mutations that happen in sperm or egg cells that you might pass along to the next generation. And a growing chorus of technologies is poised to alter harmful mutations in human genes that make life difficult, such as recent success in altering the genes in lung cells that cause cystic fibrosis.
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Nearly every animal must make a living with a set of genes that remains virtually unchanged during their lifetime, but a recent study of tropical reef building corals shows something different. These very long-lived animals are constantly changing and testing their genes - and some of these changes make it into the next generation. In this way a centuries-old coral might be a cauldron of genetic innovation, and it might help prepare them for climate change.
The new data come from the PhD work of Elora López-Nandam and her colleagues in Steve Palumbi’s lab at Hopkins Marine Station at Stanford University, published this week in the Proceedings of the Royal Society. With help from the Chan Zuckerberg BioHub, López-Nandam looked very carefully at genomes of corals by taking samples from different branches of these tree-like animals. Full genome sequences showed hundreds of places in each individual branch where the DNA was slightly different – these differences represent localized mutations in these branches. Then she and collaborator Rebecca Albright used a new facility at the California Academy of Sciences to spawn these same corals and look at which of the mutations were passed to the gametes. Much to their surprise, because it does not happen this way in humans or most animals, many of the mutations in the normal tissues of the corals were passed on to the gametes. This means that mutations that occur during the growth of corals can then jump to offspring in the next generation.
But passing mutations on to your offspring can burden them with potentially bad genes. This is why most animals do not pass along the mutations that occur in their normal tissues like skin. The López-Nandam study shows that corals reduce this problem by filtering mutations before being delivered into the next generation. By examining where each mutation appears in the genome, the authors could find the changes that alter a protein sequence and ones that did not. Random mutations change protein genes at well-known rates, and these mutations are often the deleterious ones that cause genetic disease. The López-Nandam study found that the mutations that made it into the next coral generation had far fewer protein changes. This means that the corals were somehow filtering out the most likely deleterious mutations, and passing on changes that did not hurt the coral cells or that potentially benefited them.
Overall, this study agrees with previous studies that found mutations in the tissues of large, long-lived corals are evolutionarily important. These mutations can add to the genetic diversity of coral populations and increase their ability to adapt to new conditions. In most animals this process also happens when offspring inherit new mutations that happen in the eggs and sperm of their parents, but takes many generations.
The López-Nandam study goes a step further and shows that this adaptive process can happen within a single coral colony in a single generation: mutations are filtered to remove the harmful ones, potentially giving rise to patches of coral with new adaptive alleles…maybe even new mutations that can help counteract some of the stresses of climate-induced heat waves.
Reference: López-Nandam EH, Albright R, Hanson EA, Sheets EA, Palumbi SR. Mutations in coral soma and sperm imply lifelong stem cell renewal and cell lineage selection. Proc Royal Soc B. 2023;290(1991):20221766. doi: 10.1098/rspb.2022.1766.
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