In the last two years, the Great Barrier Reef has lost 50 percent of all its corals. The 2016-2017 disaster was just the latest in a series of three global coral bleaching events that have been slowly decimating reefs since the 1980s, leading so far to the destruction of 27 percent of the world's reefs. As conservationists are scrambling to find innovative ways to combat the effects of widespread coral bleaching, a new solution might present itself in the field of genetics.
Stanford Medicine has announced that a project is underway to explore the future potential of gene editing so that it one day might be used to save the dying corals. The idea behind this project is to understand "what genes are critical to coral biology," explains Stanford geneticist Phillip Cleves.
"What we really want to do is figure out the basic mechanisms of how coral works and use that to inform conservation efforts in the future."Cleves has already conducted a proof-of-principle study, featured yesterday in the journal Proceedings of the National Academy of Sciences, in which he successfully modified coral genes using the CRISPR-Cas9 gene-editing tool.
His was the first-ever successful attempt to use CRISPR-Cas9 on coral, Stanford Medicine revealed, noting that the study offered conclusive evidence that the gene-editing tool "could be a potent resource for coral biologists."
"Up until now, there hasn't been a way to ask whether a gene whose expression correlates with coral survival actually plays a causative role," Cleves said.
"There's been no method to modify genes in coral and then ask what the consequences are," he pointed out.
And that is just exactly what Cleves is trying to achieve. He stated that he views his study as an "early blueprint" for the type of work that can be done in the future in order to give corals a helping hand.
For now, the geneticist is trying to find out whether the coral genome contains genes that can help these animals establish new colonies or that perhaps can make them more resistant to the rising ocean temperatures.His study focused on Acropora millepora corals, in which he successfully modified three types of genes: red fluorescent protein, green fluorescent protein, and fibroblast growth factor 1a.
According to Stanford Medicine, Cleves' team tweaked the genes to switch them off and see what would happen. In the case of the first two genes, this proved to be tricky work, since both genes have multiple copies in the genome, so switching off one copy to stop it from glowing didn't turn off its replicas as well.
"Although we are not sure we saw convincing loss of fluorescence, DNA sequencing showed us that we were able to molecularly target both the red and the green fluorescent protein genes," Cleves explained in the news release.
However, in the case of the third gene — which scientists believe helps regulate new coral colonization and which has only one copy in the genome — CRISPR-Cas9 produced mutations in the coral embryos, proving that the gene-editing tool can modify single-copy coral genes.
But using CRISPR-Cas9 on corals was not without some challenges. Since the procedure requires a fertilized egg (or zygote) to work, and coral spawning occurs only once or twice a year and is only triggered by the rise of a full moon, Cleves had to carefully time the zygote-collecting process. For this purpose, he enlisted the help of researchers at the Australian Institute of Marine Science, who guided him throughout the process.
Going forward, Cleves hopes that geneticists will one day use the CRISPR-Cas9 tool to target genes that are potentially involved in bleaching — a process that takes place when sea surface temperatures rise and in which corals expel the algae that live in their tissues, becoming completely white.
Other genes that could be studied in the future include those that regulate skeletal growth or the symbiotic relationship that corals have with algae.
"This is an all-hands-on-deck moment," Cleves pointed out.
"If we can start classifying what genes are important, then we can get an idea of what we can do to help conservation, or even just to predict what going to happen in the future. And I think that makes this a really exciting time to be a basic biologist looking at the genetics of coral," he said.