Human beings are not the only animal that suffers from cancer. What's more, there are some rare types that do not affect us. This is the case of two types of cancer that occur among cockles, which have been affecting this mollusk for hundreds, possibly thousands of years. Its peculiarity: it is transmitted through water. Now, a team made up of researchers from the Wellcome Sanger Institute, the CiMUS research center at the University of Santiago de Compostela in Spain, and collaborators from several countries, has discovered that these cockle tumors are highly genetically unstable: cancer cells within a tumor alone contained very different numbers of chromosomes, something not seen in other cancers. The conclusions have just been published in 'Nature Cancer'. There are more than 205 species of cockles around the world. They also belong to one of the oldest groups of animals on Earth: bivalve mollusks. These beings have inhabited the Earth for more than 500 million years. As a fact: they appeared 300 million years before the dinosaurs. But, despite being the 'usual suspects' of life on our planet, they also suffer from cancer. In fact, a strange type, similar to leukemia, transmitted through live cancer cells that are passed from one cockle to another through sea water. Contagious cancers that infect cockles spread throughout the body and are often fatal to infected animals. In fact, cockles are not the only ones: eight independent types of this cancer (called BTN) have so far been identified in clams, cockles and mussels around the world. But, to focus the shot, the study focused on the common cockle (Cerastoderma edule), a species that lives on the coasts of Europe and northwest Africa, and is often collected for food. In fact, not only the genome of these cancers was sequenced, but also that of the cockle itself, being the most complete to date. "Transmissible marine cancers are less understood than contagious cancers in species such as dogs and Tasmanian devils, due to the lack of robust reference genomes of the animals they affect," says Zemin Ning of the Wellcome Sanger Institute and one of the authors of the study. »Our study provides the top-quality reference genome of the common cockle, which is vital if we are to discover and understand the genetic changes observed in cockle cancers. "To continue learning about transmissible cancers, it is important to continue providing quality genetic data on the affected species." 7,000 cockles collected around the world The team collected around 7,000 cockles in 36 locations in 11 countries, including Spain, Portugal, the United Kingdom, Ireland and Morocco. From this, they genetically sequenced 61 tumors and were able to show the existence of two different types of BTN. They even found several cockles that had unexpectedly been infected by cells from both forms of cancer at the same time. By genetically tracking the evolution of tumors, they found multiple types of changes, including evidence that cancer cells had captured mitochondria (the small organelles that generate the cell's energy) from their cockle hosts at least seven times in the past. . An ancient cancer While it is difficult to accurately estimate the age of cockle cancers, the findings of this study suggest that these cancers likely emerged centuries or even millennia ago. The authors' opinion is that they have spread slowly through European cockle populations, occasionally capturing mitochondria from host cells as replacements for their own when they become damaged. "Tumors were first found in cockles about 40 years ago, but our study is one of the first to sequence and genetically analyze the entire process," says Alicia Bruzos, researcher at CiMUS -Universidade de Santiago de Compostela during the research and coautra del estuo. «We clarified the existence of two independent transmissible cancers, although we suspect that there are many more different types. "Having a broader view of the different types of transmissible cancers can give us more information about the conditions necessary for tumors to evolve and survive in the long term." Unstable cancers In particular, the team found that the genomes of BTN tumors are very unstable: the number and size of chromosomes varied markedly between different tumors and between cells of the same tumor. For example, some cells contained as few as 11 chromosomes and others as many as 354 (the number of chromosomes in normal cockle cells is 38). This degree of “chromosomal instability” is much greater than any previous observation in human tumors and suggests that a stable genome is not necessary for the long-term survival of these transmissible cancers. This is surprising, since human cancer cells cannot survive high levels of chromosomal instability, although moderate levels often make tumors more likely to spread to other organs and become resistant to treatment. Understanding more about how BTN cells tolerate this instability could help inform new approaches to targeting human cancer cells in the future. Furthermore, understanding the BTN and its impact is vital to protecting cockle populations from future threats. Sometimes transmissible cancers can combine with many other factors, such as pollution, rising sea temperatures and viral outbreaks, to trigger mass mortality events, killing more than 90% of cockles in a given area. MORE INFORMATION news No Astronomers, on the warpath against satellite constellations: "The sky is also the heritage of humanity" news No The meteorite that split a mountain in two "Cockles are an important part of the life of many people in Europe and are a crucial part of coastal ecosystems," concludes Adrián Báez-Ortega, from the Wellcome Sanger Institute and lead author of the study. »They have existed for many millions of years, but now face a variety of threats of which transmissible cancers are just one example. Understanding more about the origins and evolution of transmissible cockle cancers, and how their cells interact with cockle cells and the marine environment, could help protect animal populations in the future, while also providing insights into how Cancers can survive for thousands of years as marine parasites."
