/https://tf-cmsv2-smithsonianmag-media.s3.amazonaws.com/filer/6e/b3/6eb39914-a950-40f7-80ab-a547ca735487/cc5bc2.jpg )
An international scientific team made up of more than 40 authors from 7 different countries, led by Juan Pascual Anaya, PhD, a researcher at the University of Malaga (UMA) in Spain, has managed to sequence the first genome of the myxini – also known as “hagfish”–, the only large group of vertebrates for which there was no reference genome of any of its species yet. This finding, published January 12, 2024 in Nature Ecology & Evolution, has allowed deciphering the evolutionary history of genome duplications – number of times a genome is completely duplicated – that occurred in the ancestors of vertebrates, a group that comprises human beings. The article is titled “Hagfish Genome Sequence Sheds Light on Early Vertebrate Genome Evolution.”
“This study has important implications in the evolutionary and molecular field, as it helps us understand the changes in the genome that accompanied the origin of vertebrates and their most unique structures, such as the complex brain, the jaw and the limbs,” explains Dr. Anaya, the scientist of the Department of Animal Biology of the UMA, who has coordinated the research.
Thus, this study, which has taken almost a decade, has been carried out by an international consortium that includes more than 30 institutions from Spain, the United Kingdom, Japan, China, Italy, Norway, and the United States, including the University of Tokyo, the Japan research institute RIKEN, the Chinese Academy of Science, and the Centre for Genomic Regulation in Barcelona, among others.
Ecological Link
The myxini or “hagfish” are a group of animals that inhabit deep ocean areas. Known for the amount of mucosa they release when they feel threatened – a focus of research of cosmetic companies – and, also, for their role as an ecological link in the seabed – because they are scavengers and are responsible for eliminating, among other things, the corpses of whales that end up at the bottom of the sea after dying –; hitherto their genome had not been sequenced due to its complexity, because it is composed of a large number of microchromosomes, which, in turn, are composed of repetitive sequences. This is in addition to the difficulty of accessing biological material.
“Besides, these microchromosomes are lost during the development of the animal, so that only the genital organs maintain a whole genome,” says Dr. Anaya.
Genome Duplications
To be more specific, for this study, in collaboration with the Chinese Academy of Science, the genome that has been sequenced is that of the Eptatretus burgeri, which lives in the Pacific, on the coasts of East Asia. To achieve this, the researchers generated data up to 400 times the size of its genome, using advanced techniques – Hi-C – of chromosomal proximity and managing to assemble it at chromosome level.
“This is important because it allowed us to compare, for example, the order of genes between this and the rest of vertebrates, including sharks and humans, and, thus, solve one of the most important open debates in genomic evolution: the number of genome duplications, and when these occurred during the origin of the different vertebrate lineages,” says the UMA scientist Dr. Anaya, who adds that, thanks to this, we now know that the common ancestor of all vertebrates derived from a species whose genome was completely duplicated once.
Later, according to Dr. Anaya, the lineages that gave rise to modern mandibular and non-mandibular vertebrates separated, and each of these re-multiplied its genome independently: while the former, which include humans, duplicated it, the latter tripled it.
Evolutionary Impact
An analysis of the functionality of genomes, based on extremely rare samples of myxini embryos, carried out in the prestigious laboratory of Professor Shigeru Kuratani of RIKEN; and a study on the possible impact of genome duplications on each vertebrate, developed together with the Phil Donoghue, PhD, Professor at the University of Bristol and member of the Royal Society, complete this multidisciplinary research that is key to understanding the evolutionary history of vertebrates, because it provides perspectives on the genomic events that, probably, drove the appearance of important characteristics of vertebrates, such as brain structure, sensory organs, or neural crest cells, among them, an increase in regulatory complexity, that is, a greater number of switches that turn genes on/off.