Scientists have sequenced the largest animal mitochondrial genome, that of the tube anemone.
The tube anemone is found in the Atlantic from the coast of Patagonia in Argentina as far north as the East Coast of the US. Its mitochrondial genome has 80,923 base pairs, meaning it is the largest animal mitochondrial genome to be sequenced to date.
The shape of the mitogenomes in the two species of tube anemone were surprising. According to the researchers, despite the fact the gene sequences of these closely related species should be similar, the I. nocturnus has five chromosomes while P. magnus has eight. This type of variation has previously only been found in medusozoans, sponges, and some crustaceans. Stampar commented: “Humans and bony fish species are more similar than these two tube anemones in terms of the structure of their mitochondrial DNA.”
The difficulty of sequencing the largest animal mitochondrial genome
The animals’ elusive behaviour is an obstacle to sequencing the genome. When faced with a threat, the tube anemone hides in the long leathery tube it has that distinguishes it from true anemones.
Sérgio Nascimento Stampar, a professor in São Paulo State University‘s School of Sciences and Letters (FCL-UNESP) at Assis in Brazil and the leader of the study, explained: “You have to dig a hole around it, sometimes as deep as a meter, and stop up the part of the tube buried in sand. All this must be done under water while carrying diving gear. Otherwise, it hides in the buried part of the tube and you simply can’t get hold of it.”
Comparing the tube anemone to the human genome
Stampar said: “I. nocturnus‘s mitogenome is almost five times the size of the human mitogenome. We tend to think we’re molecularly more complex, but actually our genome has been more ‘filtered’ during our evolution. Keeping this giant genome is probably more costly in terms of energy expenditure.”