Tiny, durable tardigrades take up a mishmash of genes from plants, bacteria

Turns out tardigrades, the nearly microscopic animals known for their ability to survive in extreme environments, have been promiscuous in their borrowing of genes obtained directly from other species, making them the only animals known to have undergone extensive horizontal gene transfer. Sequencing of the tardigrade genome, as reported in Proceedings of the National Academy of Sciences in November 2015, reveals that a stunning 17% consists of genes from a wide variety of sources, including bacteria, fungi, viruses, and plants. The foreign genetic material is not clustered together, but spread fairly uniformly throughout the animal’s genome. Assimilated genes have since acquired properties characteristic of animal genes, such as intron regulatory elements, the research team found. Further analysis revealed that the most abundant acquired genes encode catalases, antioxidant enzymes involved in neutralizing oxidative conditions that might damage cells under environmental stress. Tardigrades also acquire DNA-repair genes and other genes known to mitigate damage to cells caused by extreme environmental conditions. The authors suggest that tardigrades may be more prone to picking up genes from their environment during the transition from desiccation to rehydration, when cell membranes become transiently leaky. When combined with desiccation-induced breaks in double-stranded DNA, the newly introduced foreign DNA may be more likely, they suggest, to become a permanent resident of the tardigrade genome. —Karyn Hede, News Editor

More kids genetically predisposed to cancer than previously understood

At least 8% of children with cancer have heritable genetic alterations that may have predisposed them to the disease, according to a large genomic study published in the New England Journal of Medicine. The surprising results, which may change clinical practice, suggest that comprehensive genomic screening may be warranted for all pediatric cancer patients, not just those with a family history of cancer. The study of 1,120 pediatric cancer patients, led by investigators from the Pediatric Cancer Genome Project at St. Jude Children’s Research Hospital, Memphis, TN, and Washington University School of Medicine, St. Louis, MO, overturns the idea that germ-line mutations in pediatric cancer patients are rare and occur only in children with a family history of cancer. More than half of the 95 children with germ-line mutations in genes associated with autosomal dominant hereditary cancer predisposition syndromes had no family history of cancer. Perhaps most surprising, eight patients harbored mutations in BRCA1, BRCA2, or PALB2—genes thought to predispose adults, not children, to cancer. The findings suggest that mutations in BRCA1 and BRCA2 are more common in pediatric cancers than is currently understood and have clearly important implications for management of children and their extended families. Additionally, 109 children (9.7%) had germ-line mutations in other cancer-associated genes. In comparison, only 1% of 966 adult controls from the 1000 Genomes Project had alterations in these same genes. The study “lays the groundwork to understand the spectrum of cancers and age-specific cancer risks associated with germline mutations in predisposition genes and how best to monitor at-risk patients and families,” stated investigator Kim Nichols, director of the St. Jude Hereditary Cancer Predisposition Clinic. St. Jude has now launched Genomes for Kids (G4K), to sequence the genomes of eligible pediatric cancer patients who enter the hospital for treatment. —Karyn Hede, News Editor