The asexual clonal crayfish that could teach us about tumor development
Marmorkrebs, or marbled crayfish, have an extraordinary ability. Not only can they reproduce excessively in the wild, but a new study from the German Cancer Research Center (DKFZ) has revealed that the entire species originates from a single mother crayfish, who cloned herself in an aquarium almost 30 years ago. This clonal genome evolution is phenomenal in itself, but it may also help to explain processes in the development of cancerous tumors.
A few decades ago, the Marmorkrebs clone split from the slough crayfish (Procambarus fallax), an animal endemic to the Florida Everglades, and evolved into a separate species (Procambarus virginalis). Reproducing via parthenogenesis, an asexual form of reproduction whereby embryos develop without fertilization, the all-female offspring of the crustacean are believed to be essentially identical in their genome sequences, with few differences that can be chalked up to natural mutations.
"We could detect only a few hundred variants in a genome that is larger than the human genome," says Frank Lyko, lead researcher of the study. "That is an incredibly small number."
In the entire genome sequenced from 11 individual marbled crayfish, the DKFZ researchers counted 3.5 billion base pairs, making it seven percent larger than the human genome.
To add to their repertoire of amazing traits, marbled crayfish are also highly adaptable to a wide variety of habitats and have been found in Sweden, Japan, Germany and even subtropical Madagascar. Marmorkrebs in these locations are either released or aquarium escapees, and the rapid growth in their numbers is testament to their adaptability, and worrying for ecologists.
"It was known that the crayfish can establish itself in the wild after releases from the aquarium," Lyko says. "But the news was that it can spread so rapidly and massively."
Despite not having a mix of paternal and maternal genes to enlarges genetic variety, Marmorkrebs are able to rapidly adapt to different environmental conditions using epigenetic mechanisms. These regulate the interpretation of genetic information, working like switches to turn genes on or off.
"Epigenetic variants are often influenced by genetic variants," says Lyko, "In Marmorkrebs, however, epigenetic variation is independent, because there is virtually no genetic variation."
Here's where it becomes quite interesting for cancer researchers. Like Marmorkrebs, tumor genomes evolve clonally from a single original cell and can adapt to their environment. Epigenetic mechanisms play a role in this process, along with chance mutations, genetic drift and selective pressures, so the marbled crayfish gives scientists the opportunity to study the influence of these factors.
The scientists hope that uncovering which environmental factors impact epigenetics and gene regulation in the marbled crayfish will provide knowledge that is applicable to tumor development and open up new avenues for treatment.
The study was published in Nature's journal Nature Ecology & Evolution.
Source: German Cancer Research Center