Tuesday, July 13, 2010

Endogenous filoviruses

Readers will recall Liu and Soper's exogenation hypothesis for the origin of retroviruses. They speculated that retroviruses - like the AIDS virus HIV - originated as escaped particles from what were originally endogenous parts of certain eukaryotic genomes (like our own). While I like the idea of thinking backwards from the standard evolutionary model to come up with a creationist idea, I always found their hypothesis a bit limiting. It could really only explain retroviruses, which are just one family among many different types of viruses. In relation to that shortcoming, I previously noted the discovery of remnants of a bornavirus in mammalian genomes, but they were just fragments that looked more like insertions. Now, Taylor et al. report evidence of filovirus-like sequences in some mammals. You'll recall filoviruses as causative agents of the notorious ebola hemorrhagic fever.

From a creationist perspective, this report is complicated by the phylogenetic analyses of the filovirus-like sequences. They show that the filovirus sequences are nested within a clade of mammalian sequences. So we creationists have to wonder whether they represent true insertion events or whether they were created there to begin with (as Liu and Soper hypothesize for the retroviruses). It's not an easy question to answer from their phylogenies, since the true virus proteins are just as divergent as the mammalian copies, and the various mammal species tested (esp. kangaroo Macropus) are present in multiple copies. What we would really like to know is whether any of these putative insertions exist at homologous chromosomal sites in mammals that are likely to be of different baramins. That would suggest that they were created there rather than inserted. It's an interesting report nonetheless.

Taylor et al. 2010. Filoviruses are ancient and integrated into mammalian genomes. BMC Evolutionary Biology 10:193.

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