![]() Many scientists assume that the immune system, once established, would evolve only in one direction, “towards becoming more adaptive and more specific,” Fassati says. To University College London immunologist and virologist Ariberto Fassati, who wasn’t involved in the study, the results are astonishing. In the case of multiple mates, this was marked by even more changes, such as the blunting of antibody responses, and the loss of rag genes. ![]() While temporary attachment only seemed to require reduced antibody responses, permanent one-to-one fusions seemed to be associated also with the curtailing of cytotoxic T cell function. Overall, the more extreme attachment between mates, the more extreme the changes to adaptive immunity genes appeared to be, the team notes. Certain rag genes, which are also involved in antibody formation, had amassed deleterious mutations in species that mate as groups of males, whereas those genes were relatively intact in species that pair in a one-to-one fashion such as C. Although many of these genes seemed to be intact in most of the anglerfish species, they found that aicda, which plays an important role in creating specific antibodies, was effectively absent in all 10 species that form temporary or permanent attachments, whereas it was intact in the three control species. Pietsch, University of Washingtonīecause antibodies directed against foreign tissue are also known to cause complications in patients during tissue transplants, the team also looked at certain genes that underpin antibody generation. In all six permanent attachers, for instance, two genes that encode such receptors were entirely missing, suggesting that dismantling the cytotoxic reactivity of T cells might be necessary to allow different anglerfish individuals to mate. The researchers also found alterations in the genes encoding receptors of the cytotoxic T cells that interact with the MHC class I proteins. Interestingly, the six permanently attaching species all showed unusual, significant alterations to their MHC genes, which were even more severe in the three species in which multiple males fuse with each female. It’s the MHC class I receptors that drive cytotoxic T cells to attack foreign cells in tissue transplant settings. ![]() First, they looked at genes that encode the fishes’ major histocompatibility complex (MHC) class I and II proteins, cell surface molecules that differ between individuals and enable T cells to distinguish the body’s own cells from foreign ones. ![]() The team examined a handful of well-characterized genes known to be key players in the adaptive immune response. The team also included three control species from other anglerfish groups in which males never attach to females. That included four species that mate by temporary attachment and six species that form permanent fusions-three of them in a one-to-one fashion, and three that have multiple males fuse with a single female. Biological samples from the deep sea are hard to come by, but with the help of ichthyologist Theodore Pietsch, an expert on deep-sea anglerfishes at the University of Washington, the team was able to obtain tissue samples from several specimen collections.īoehm and his colleagues sequenced the DNA from 31 specimens, representing 13 species of deep-sea anglerfish. Immunologist Thomas Boehm and his colleagues at the Max Planck Institute of Immunology and Epigenetics in Germany long wanted to know how some anglerfish species can form bodily fusions between individuals, and set out to do an analysis of the animals’ genomes. Evolution produces all sorts of wacky outcomes, and this is one of them.” “I suppose we shouldn’t have too many preconceptions about what is and isn’t possible in nature. “It’s quite shocking,” remarks geneticist Elizabeth Murchison of the University of Cambridge who wasn’t involved in the study. ![]() Over the course of evolution, changes in genes involved in antibody production and cytotoxic T cell responses may have paved the way for the animals’ strange reproductive habits, while for scientists it raises questions about how the fish defend themselves against pathogens in the deep sea. The genomes of species that temporarily or permanently fuse with their mates have undergone radical alterations of key genes that underpin adaptive immunity-a branch of the immune system responsible for the rejection of foreign tissue-making some of them the first known instances of vertebrates that effectively lack an adaptive immune system. A new genomic analysis of 13 anglerfish species published today (July 30) in Science provides some clues. ![]()
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