Transcriptional Control of an Essential Ribozyme in Drosophila Reveals an Ancient Evolutionary Divide in Animals
Figure 6
Model for the evolutionary history of RPR.
A. An ancestral RPR gene is thought to have undergone gene duplication and one of the daughter genes assumed the new functions of MRP RNA (neofunctionalization). MRP RNA is transcribed by pol III in all animals, as is RPR in animals previously characterized. We found that the RPR gene in crustaceans and insects has undergone another genetic event that inserted it, devoid of pol III signals, into a pol II-transcribed gene. B. A cladogram showing arthropod evolution (based on, [26], [27], [65]). In Hexapods and true crustaceans (Vericrustacea) (light grey), RPR is embedded in a pol II-regulated gene. In contrast, in Myriapoda and Chelicerata, RPR is a pol III gene (dark grey). The RPR genes in Remipedia and Oligostraca have not been characterized due to lack of genomic sequences (unshaded). The arrow indicates a node that connects branches where RPR is found in a recipient gene. These groups are thought to have diverged 500 million years ago [18], [66]. We predict that Remipedia RPR is also embedded in a recipient gene similar to the sister group Hexapoda. An analysis of RPR in Oligostraca will enable us to determine if embedding of RPR occurred earlier in arthropod evolution in an ancestor of all pancrustaceans.