The Changeable Coelacanth: Not Strictly a “Living Fossil”
Fields covered: Evolutionary Genetics, Molecular Biology
§ Diverse Eukaryotic CGG-Binding Proteins Produced by Independent Domestications of hAT Transposons (Open source) § Interspecies Insertion Polymorphism Analysis Reveals Recent Activity of Transposable Elements in Extant Coelacanths (Open source) |
Yes, today’s coelacanths may seem morphologically unchanged from their fossilised ancestors that lived 65 million years ago. But their genome—as scientists have discovered—tells quite a different story.
Flying in the face of the long-held belief that the coelacanth’s morphological stasis was due to a slow-evolving (or not evolving) genome, genetic sequencing has shown that the coelacanth Latimeria chalumnae has, in fact, undergone widespread evolution.
Scientists arrived at this conclusion rather serendipitously; while searching databases for CGGBP1 (an ancestral human gene involved in gene regulation), they found that L. chalumnae had mysteriously acquired a whopping 62 new variations of this gene around 10 million years ago.
But that’s not the really surprising part. These new genes did not share a common ancestor with one another, which suggests that they were somehow acquired from other species—via horizontal gene transfer. How is that possible though? The answer: Transposons, DNA sequences which jump around and between genomes almost like viruses.
By analysing the sequences of the coelacanth CGGBP1 genes, scientists found that 47 out of 62 contained full BED zinc finger and Hermes DNA binding and protein dimerization domains. These domains are encoded by transposons belonging to the hAT family, so their presence in coelacanth CGGBP1 genes practically screams the work of transposons.
Transposons could have been integrated into the coelacanth genome, then lost their ability to jump. Ostensibly, the 62 genes thus introduced were so functionally useful (or functionally neutral) to the coelacanth that they were conserved over time.
Because CGGBP1 is probably involved in gene regulation in coelacanths, subtle changes (or in this case, additions) could have huge evolutionary impacts.
Who knows? Give or take a few thousands of millennia, we could very well be seeing new coelacanth species popping up!