Genome of living fossil revealed

The coelocanth is a five-foot-long fish that lives in deep-sea caves, and which hasn't changed in three hundred million years. Image: IMCB

Coelocanth: Close-up of head
Coelocanth: close-up of head. Image: IMCB
May 25, 2014 – The African coelacanth has brought an international team of scientists together to crack its genomic code. Findings from the study are providing new insights into the evolutionary history of this fish and new clues about aquatic creatures transitioned to life on land.

A coelacanth is what is known as a "living fossil," an organism that has survived unchanged for millions of years. The skeletons of modern coelacanths are nearly indistinguishable from the 300-million-year-old skeletons of their fossilized ancestors. By sequencing the genome of these fish and comparing it to the genes of other vertebrates, the researchers have uncovered information about the genetic changes that helped aquatic animals transition from water to land. The findings include many genes and regulatory elements gained and genes lost when vertebrates came on land. Their research findings appear in the journal Nature.

A salient feature of the coelacanth is its fleshy fins, which resemble the limbs of land animals. The team has found several important regions of the genome used in the formation of limbs, which suggest that four-legged land animals (tetrapods) adopted these sequences from coelacanths to help them form limbs. The researchers also found that there are many regulatory changes that influence genes involved in the perception of smell, as creatures that transitioned to land needed new means of detecting chemicals in their environment.

Prof. Byrappa Venkatesh, Research Director of the Institute of Molecular and Cell Biology, whose group was involved in the project, said, "The coelacanth with its distinctive fleshy fins represents an intermediary phase in the evolution of land animals from aquatic fishes. By comparing the genomes of coelacanth, human and other vertebrates, our group has been able to discover gene regulatory elements that played a key role in the development of our limbs and fingers as well as our ability to detect airborne odorants."

While sequencing the genome of the coelacanth has provided some answers, future investigation of the coelacanth's physiology -- particularly that of its respiratory, immune and reproductive systems -- will further show us how some vertebrates were able to adapt to land while others remained in the water.

Adapted from materials obtained from AAAS

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