A group of Brazilian scientists claim to have sequenced the largest mitochondrial genome of those already sequenced previously. The mitochondrial genome (mitogenome) is represented by the DNA contained in the mitochondria, the cellular organelles that in turn are found in the eukaryotic cells. It is only a small portion of the DNA of an animal eukaryotic cell since most of it is found in the nucleus of the cell (in this case we speak of nuclear genome or nuclear DNA).
Scientists at the University of São Paulo (FCL-UNESP), Assis, Brazil, have in fact sequenced the mitochondrial genome of Isarachnanthus nocturnus, a tubular sea anemone only 15 cm long but which boasts, in relation to its body, a long mitochondrial genome consisting of 80,923 base pairs (the human mitochondrial genome includes only 16,569 base pairs).
The results, published in Scientific Reports, therefore confirm that the mitogenome of the I. nocturnus is almost five times larger than the human one, as stated by Sérgio Nascimento Stampar, professor at FCL-UNESP and principal author of the study, who adds: “We tend to think that we are molecularly more complex, but in reality our genome has been more ‘filtered’ during our evolution. Maintaining this giant genome is probably more expensive in terms of energy expenditure.”
Among other things, this same sequencing puts on the table the possibility of a reclassification of the species of cnidarians (jellyfish, octopus, corals and sea anemones) since the tubular anemones analyzed seem to form a group separated from corals and other sea anemones and show similarities with jellyfish.
More data and more studies will be needed, perhaps focusing on the sequencing of the nuclear genome of these species, a result that Stampar intends to achieve by the end of 2020.