Comb jellies reveal ancient origins of animal genome regulation

Life depends on genes being switched on and off at exactly the right time. Even the simplest living organisms do this, but usually over short distances across the DNA sequence, with the on/off switch typically right next to a gene. This basic form of genomic regulation is probably as old as life on Earth. A new study published in Nature by researchers at the Centre for Genomic Regulation (CRG) and the Centre Nacional d’Anàlisi Genòmica (CNAG) finds that the ability to control genes from far away, over many tens of thousands of DNA letters, evolved between 650 and 700 million years ago. It probably appeared at the very dawn of animal evolution, around 150 million years earlier than previously thought. The critical innovation likely originated in a sea creature, the common ancestor or all extant animals. The ancient animal evolved the ability to fold DNA in a controlled manner, creating loops in three-dimensional space that brought far-flung bits of DNA in direct contact with each other. The discovery was made by exploring the genomes of many of the oldest branches on the animal family tree, including comb jellies like the ‘sea walnut’ (Mnemiopsis leidyi), placozoans, cnidarians, and sponges and single-celled relatives of animals.

Two comb jellies can fuse together into one–and keep both butts

They heal. They poop. They live on.

File:Sea Walnut (Mnemiopsis leidyi) - Bærum, Norway 2021-08-15 (04).jpg - Wikimedia Commons

File:Sea Walnut (Mnemiopsis leidyi) - Bærum, Norway 2021-08-15 (03).jpg - Wikimedia Commons

File:Sea Walnut (Mnemiopsis leidyi) - Bærum, Norway 2021-08-15 (02).jpg - Wikimedia Commons

New forms of animals made by fusing several comb jellies together

Parts from dozens of different individual comb jellies have been fused together to create strange new animals unlike anything seen before

Scientists accidentally find deep-sea 'jelly' creatures merged into 'single entity' after injury, revealing bizarre new behavior

Researchers discovered that some comb jellies can fuse their bodies together when injured. The unique adaptation, which involves merging their nervous systems and stomachs, has never been seen in any other species.

Scientists accidentally find deep-sea 'jelly' creatures merged into 'single entity' after injury, revealing bizarre new behavior

Researchers discovered that some comb jellies can fuse their bodies together when injured. The unique adaptation, which involves merging their nervous systems and stomachs, has never been seen in any other species.

After injury, one species of comb jelly can fuse to become one

Researchers reporting in the journal Current Biology on October 7 have made the surprising discovery that one species of comb jelly (Mnemiopsis leidyi) can fuse, such that two individuals readily turn into one following an injury. Afterwards, they rapidly synchronize their muscle contractions and merge digestive tracts to share food.