Gene organization and evolution of mitochondrial genomes from two invertebrate phyla: Vestimentifera and Chaetognatha.

摘要

Information concerning DNA sequence comparisons and gene organization of animal mitochondrial DNA has proven extremely valuable in determining relationships of animal groups. Within the vertebrates, only two gene rearrangements are known. A single major rearrangement separates the vertebrates from the echinoderms, while three major rearrangements distinguish these groups from the insect gene organization. In contrast, nematodes and the mollusc Mytilis have extensive differences from arrangements of other animal groups.;In this thesis, I have used the polymerase chain reaction and direct sequencing to obtain partial sequence and gene organization for members of two enigmatic phyla: Vestimentifera (deep sea vent tube-worms) and Chaetognatha (arrow worms). Approximately one-third of the mitochondrial genome was determined for both groups.;The organization of the vestimentiferan genome bears some similarities to those of vertebrates and insects. In particular, the subunits of cytochrome oxidase (COI-COIII) and ATPase appear in the same order: COI, COII, ATPase 8, COIII. In addition, the two ribosomal RNA genes are transcribed in the same direction and are separated by tRNA valine gene, as occurs in vertebrates and insects. One major difference, however, is the removal of the ATPase 6 gene from its position between ATPase 8 and COIII. This change clearly separates them from those phyla.;The chaetognath gene organization bears no similarities to that of any other known phylum, and suggests that this group separated from other groups very early in the history of the animal kingdom. The large ribosomal RNA gene has been separated from the small RNA gene, and is located adjacent to the structural gene for COI. The cytochrome b gene has been rearranged to the region upstream the 5