Largest animal genome ever: South American lungfish

Amazing stuff!

"... “With over 90 gigabases (in other words, 90 billion bases), the DNA of the South American species is the largest of all animal genomes and more than twice as large as the genome of the previous record holder, the Australian lungfish,”  ...

The researchers found that “autonomous transposons” are responsible for the South American lungfish’s enormous genome. Also known as “jumping genes”, these are DNA sequences that can copy and paste themselves throughout the genome and causing it to expand. ...

The new analysis shows that the expansion rate of the South American lungfish genome is the fastest ever seen – growing by the size of the entire human genome every 10 million years. ..."

"... The genetic material of the South American lungfish in particular breaks all records for size: “With over 90 gigabases (in other words, 90 billion bases), the DNA of the South American species is the largest of all animal genomes and more than twice as large as the genome of the previous record holder, the Australian lungfish. 18 of the 19 chromosomes of the South American lungfish are each individually larger than the entire human genome with its almost 3 billion bases,” says Meyer. Autonomous transposons are responsible for the fact that the lungfish genome has ballooned to this enormous size over time. These are DNA sequences that “replicate” and then change their position in the genome, which in turn causes the genome to grow. ...
The researchers identified the mechanism for this gigantic genome growth: The extreme expansion is at least partially due to very low piRNA abundance. This type of RNA is part of a molecular mechanism that normally silences transposons. ..."

From the abstract:

"The genomes of living lungfishes can inform on the molecular-developmental basis of the Devonian sarcopterygian fish–tetrapod transition. We de novo sequenced the genomes of the African (Protopterus annectens) and South American lungfishes (Lepidosiren paradoxa). The Lepidosiren genome (about 91 Gb, roughly 30 times the human genome) is the largest animal genome sequenced so far and more than twice the size of the Australian (Neoceratodus forsteri) and African lungfishes owing to enlarged intergenic regions and introns with high repeat content (about 90%). All lungfish genomes continue to expand as some transposable elements (TEs) are still active today. In particular, Lepidosiren’s genome grew extremely fast during the past 100 million years (Myr), adding the equivalent of one human genome every 10 Myr. This massive genome expansion seems to be related to a reduction of PIWI-interacting RNAs and C2H2 zinc-finger and Krüppel-associated box (KRAB)-domain protein genes that suppress TE expansions. Although TE abundance facilitates chromosomal rearrangements, lungfish chromosomes still conservatively reflect the ur-tetrapod karyotype. Neoceratodus’ limb-like fins still resemble those of their extinct relatives and remained phenotypically static for about 100 Myr. We show that the secondary loss of limb-like appendages in the Lepidosiren–Protopterus ancestor was probably due to loss of sonic hedgehog limb-specific enhancers."

Largest animal genome ever: South American lungfish

Decoding the world’s largest animal genome (original news release)

The genomes of all lungfish inform on genome expansion and tetrapod evolution (no public access)

South American lungfish (Lepidosiren paradoxa)