Coelacanth helps in the fight against HIV

The coelacanth has been called a "living fossil" in popular media as it is thought to have barely evolved compared to the fossil record. Despite morphological similarities of the extant coelacanth to the fossil specimen, considerable molecular evolution is likely to have occurred as seen in the case of species that have been called living fossils. However, a comparison of nucleotide sequence has shown that the rate of evolution in this lineage is significantly lower than other tetrapod lineages. The reasons for the morphological stasis have been the focus of speculation and need greater investigation. Some groups of species (including the Coelacanth) that have been characterized as living fossils are species-poor and not easily amenable to molecular evolutionary analysis. 

More than 95% of all extant fish species belong to the infraclass Teleostei (teleost fish) and abundant fish species that are commercially important or serve as model organisms (such as the zebrafish) belong to this group. These teleost fish belong to the class Actinopterygii (ray-finned fishes) and are known to have had a third round of whole-genome-duplication (3R-WGD). Phylogenetic studies have consistently found that the Coelacanths and lungfish belong to the clade of Sarcopterygii (lobe-finned fish) and share a more recent common ancestor with Tetrapods than Actinopterygii. Importantly, the Coelacanths share the two rounds of whole-genome duplication (2R-WGD) found in other tetrapods and lack the third round (3R-WGD) of whole-genome duplication found in teleost fish. This close evolutionary relationship of Coelacanths with tetrapods and its phylogenetic position has made it a useful model to study the transition of vertebrates from water to land. 

Despite the challenges associated with the study of molecular evolution of Coelacanths, sequencing of its genome in 2013 helped uncover many interesting aspects. Availability of the Coelacanth genome played an important role in timing the whole genome duplication events and provided clearer evidence to support the occurrence of vertebrate whole-genome duplication events. Identification of gene loss events in tetrapods compared to the Coelacanth highlighted several adaptive events that occurred during the transition from water to land. One of the interesting finds reported was the lack of IgM (Immunoglobulin-M) in the Coelacanth genome. Due to its strategic phylogenetic location, Coelacanth genes have been studied to understand the origin and diversification of gene families. A prominent example, the origin of the restriction factor tetherin and more recently HERC's have made use of the Coelacanth gene sequences.

Ramdas et al., use an elaborate study design to investigate the SERINC family of restriction factors. During the course of their investigation, they find that one of the human paralogs SERINC2 is not able to fight HIV while all the other four SERINCs do a good job of fighting HIV. Upon further investigation, they find that SERINC2 from the Coelacanth is able to deal with HIV and this activity was lost in other lineages. One of the most interesting aspects of this study is the use of foamy viruses similar to the endogenous one recovered from the Coelacanth genome to evaluate the ability of SERINC2. The mechanism of action is also deciphered using sophisticated assays.  You can read the final published version titled "Coelacanth SERINC2 inhibits HIV-1 infectivity and is counteracted by envelope glycoprotein from foamy virus" on the website of JVI.