About That Squid and its RNA editing �

Molecules Gone Wild

We recently reported that the common squid, Doryteuthis pealeiirecodes, uses massive, tissue-specific, RNA editing to modify many of its proteins. One evolutionary explanation for this apparent intelligent design would be that the editing machinery is merely an uncontrolled, random process. This would be in keeping with evolution�s view of life as a train off the tracks. Indeed, many past findings were initially described as vestigial or junk, until the design could no longer be denied. One current example is the finding that most of the human genome is transcribed. Apparently it is functional, and so isn�t mostly junk. But one evolutionary explanation that continues to have currency is that the transcription machinery is uncontrolled and has gone wild.

Well this �Molecules Gone Wild� explanation won�t work this time, for several reasons. First, the RNA editing is not only tissue specific, but also is protein specific. Certain proteins, such as those working on the squid nervous system, undergo much more editing than the other proteins. This doesn�t look like a random, uncontrolled, editor.

Furthermore, the RNA edits cause changes to the resulting protein amino acid sequence at a rate far higher than would be expected from random edits. And, just as striking, that non random rate is highly correlated with the editing level of the RNA site. In a given RNA transcript, some sites are found to be edited more often than others. The level of editing can range from a percent up close to 100%. And as that editing level increases, the rate at which the edits deviate from the randomly expected rate of changing the resulting protein amino acid sequence increases as well. The correlation is striking, as the graph below shows.

The horizontal red line shows the rate of amino acid sequence change that would result from random RNA edits. As you can see, for those sites that are more consistently edited, the rate increasingly rises above that red line. Something very non random is going on there, and evolution has no explanation for it aside from, �Wow, an incredibly complex design happened to arise by chance, and then it was maintained by natural selection.� That�s not science.