Lineage-specific evolution of echinoderm mitochondrial ATP synthase subunit 8

Identification of camelid specific residues in mitochondrial ATP synthase subunits

ATP synthase is an enzyme involved in oxidative phosphorylation from prokaryotic to eukaryotic cells. In mammals it comprises at least 16 subunits from which the mitochondrial encoded ATP6 and ATP8 are essential. Mitochondrial genes variations have been suggested to allow rapid human and animal adaptation to new climates and dietary conditions (Mishmar et al. 2003). Camelidae taxa are uniquely adapted to extremely hot and dry climates of African-Asian territories and to cold and hypoxic environments of the South American Andean region. We sequenced and analyzed ATP6 and ATP8 genes in all camelid species. Based on the available structural data and evolutionary conservation of the deduced proteins we identified features proper of the group. In Old World camels the ATP8, important in the assembly of the F0 complex, showed a number of positively charged residues higher than in the other aligned species. In ATP6 we found the camelid specific substitutions Q47H and I106V that occur in sites highly conserved in other species. We speculate that these changes may have functional importance.

Identification of human-specific adaptation sites of ATP6

Mitochondria play an essential role in forming ATP and generating heat. The proportion of these two depends on the coupling efficiency of electrochemical gradient to synthesize ATP. Therefore, an increased basal metabolic rate caused by partial uncoupling of the mitochondria can be balanced by a high caloric intake provided by a high-fat diet. The recent study by Mishmar et al. (Proc. Natl. Acad. Sci. USA 2003; 100: 171-176) suggested that ATP6 was the most variable gene among human mitochondrial DNAs and probably resulted from the adaptation of Homo sapiens to the colder climate during the migration out of Africa. According to this adaptation theory, the ATP6 of Homo sapiens (omnivorous animals consuming fat-containing diet) should be significantly different from that of other primates for permitting human adaptation to the dietary conditions. On the basis of this rationale, we analyzed ATP6 sequences of 136 unrelated Taiwanese subjects, which then were compared with 1,130 reported sequences. The obtained human consensus from 1,266 individuals was compared with that derived from 42 species of primates other than human. The alignment showed that human ATP6 harbored 80 variable residues, among which 25 amino acids were conserved in other primates, suggesting that adaptation constraints operating at the amino acid level results in the species-specific difference of ATP6. Therefore, these 25 amino acids are probably the human-specific adaptation residues of ATP6.

Complete mitochondrial genome sequences for Crown-of-thorns starfish Acanthaster planci and Acanthaster brevispinus

Background

The crown-of-thorns starfish, Acanthaster planci (L.), has been blamed for coral mortality in a large number of coral reef systems situated in the Indo-Pacific region. Because of its high fecundity and the long duration of the pelagic larval stage, the mechanism of outbreaks may be related to its meta-population dynamics, which should be examined by larval sampling and population genetic analysis. However, A. planci larvae have undistinguished morphological features compared with other asteroid larvae, hence it has been difficult to discriminate A. planci larvae in plankton samples without species-specific markers. Also, no tools are available to reveal the dispersal pathway of A. planci larvae. Therefore the development of highly polymorphic genetic markers has the potential to overcome these difficulties. To obtain genomic information for these purposes, the complete nucleotide sequences of the mitochondrial genome of A. planci and its putative sibling species, A. brevispinus were determined and their characteristics discussed.

Results

The complete mtDNA of A. planci and A. brevispinus are 16,234 bp and 16,254 bp in size, respectively. These values fall within the length variation range reported for other metazoan mitochondrial genomes. They contain 13 proteins, 2 rRNA, and 22 tRNA genes and the putative control region in the same order as the asteroid, Asterina pectinifera. The A + T contents of A. planci and A. brevispinus on their L strands that encode the majority of protein-coding genes are 56.3% and 56.4% respectively and are lower than that of A. pectinifera (61.2%). The percent similarity of nucleotide sequences between A. planci and A. brevispinus is found to be highest in the CO2 and CO3 regions (both 90.6%) and lowest in ND2 gene (84.2%) among the 13 protein-coding genes. In the deduced putative amino acid sequences, CO1 is highly conserved (99.2%), and ATP8 apparently evolves faster any of the other protein-coding gene (85.2%).

Conclusion

The gene arrangement, base composition, codon usage and tRNA structure of A. planci are similar to those of A. brevispinus. However, there are significant variations between A. planci and A. brevispinus. Complete mtDNA sequences are useful for the study of phylogeny, larval detection and population genetics.