Project description:We have sequenced and characterized the complete mitochondrial genome of the soft-shell clam, Mya arenaria, an important organism for environmental toxicology and aquaculture. Mya arenaria is located in the taxonomic order Myoida, which lacks any member with a completely annotated mitogenome. The M. arenaria mitochondrial genome is 17 947 bp in length. Like most marine bivalves, the circular mitogenome codes entirely on the heavy strand, with no introns. As with other bivalves, the gene order of the mitochondrion is highly rearranged. The mitogenome contains 12 protein-coding genes but ATP8 is missing, consistent with about half of all bivalve genera. Twenty-three tRNAs were identified. Phylogenetic analysis shows that M. arenaria is related most closely with the bivalves Sinonovacula constricta, and Moerella iridescens, of the infraclass Euheterodonta (unassigned). This, along with the close grouping of the phylogenetic trees, confirms a close tie between Myoida and Euheterodonta (unassigned).
Project description:Apoptosis is a fundamental feature of multicellular animals and is best understood in mammals, flies, and nematodes, with the invertebrate models being thought to represent a condition of ancestral simplicity. However, the existence of a leukemia-like cancer in the softshell clam Mya arenaria provides an opportunity to re-evaluate the evolution of the genetic machinery of apoptosis. Here, we report the whole-genome sequence for M. arenaria which we leverage with existing data to test evolutionary hypotheses on the origins of apoptosis in animals. We show that the ancestral bilaterian p53 locus, a master regulator of apoptosis, possessed a complex domain structure, in contrast to that of extant ecdysozoan p53s. Further, ecdysozoan taxa, but not chordates or lophotrochozoans like M. arenaria, show a widespread reduction in apoptosis gene copy number. Finally, phylogenetic exploration of apoptosis gene copy number reveals a striking linkage with p53 domain complexity across species. Our results challenge the current understanding of the evolution of apoptosis and highlight the ancestral complexity of the bilaterian apoptotic tool kit and its subsequent dismantlement during the ecdysozoan radiation.