Wednesday, 24 April 2013

Genome of the Coelacanth

West Indian Ocean coelacanth (Latimeria chalumnae) Wikimedia Commons

I remember how exciting it was when the second specimen of a coelacanth was caught in 1952. This "living fossil" was widely reported in the newspapers. Perhaps it was a formative moment.

Now the coelacanth genome has been sequenced and annotated (here).

The coelocanth is oviviviparous. Five fully developed young with attached yolk sacs were found in the right oviduct of a female specimen at the American Museum of Natural History (here). There was no indication of placentation but it is but a short step from ovoviviparity to placental viviparity - the more critical step being evolution of intromission.

The new report applied phylogenomics to look for genes that might have been significant in the transition from water to land. A number of developmental genes present in the coelocanth were lost in tetrapods. However, Hox genes, which determine overall body plan, were well conserved. An interesting exception was Hoxa14 and hereby hangs a tale. A conserved non-coding element associated with Hoxa14 in the coelacanth (HA14E1) was retained in tetrapods. It is speculated that it might have been recruited to coordinate nearby genes (Hoxa13, Hoxa11 and Hoxa10) that are critical in formation of mammalian fetal membranes.

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