Accelerated molecular evolution of insect orthologues of ERG28/C14orf1: a link with ecdysteroid metabolism?

We have analysed the evolution of ERG28/C14orf1, a gene coding for a protei n involved in sterol biosynthesis. While primary sequence of the protein is well conserved in all organisms able to synthesize sterols de novo, strong divergence is noticed in insects, which are cholesterol auxotrophs. In spi te of this virtual acceleration, our analysis suggests that the insect orth ologues are evolving today at rates similar to those of the remaining membe rs of the family. A plausible way to explain this acceleration and subseque nt stabilization is that Erg28 plays a role in at least two different pathw ays. Discontinuation of the cholesterogenesis pathway in insects allowed th e protein to evolve as much as the function in the other pathway was not co mpromised.