Trans-Species Polymorphism in Mitochondrial Genome of Camarodont Sea Urchins.

Evgeniy S Balakirev

doi:10.3390/genes10080592

Abstract

Mitochondrial (mt) genomes of the sea urchins Strongylocentrotus intermedius and Mesocentrotus nudus demonstrate the identical patterns of intraspecific length variability of the ND6 gene, consisting of 489 bp (S variant) and 498 bp (L variant), respectively. For both species, the ND6 length difference is due to the 488A>G substitution, which changes the stop codon TAG in S variant for a tryptophan codon TGG in L variant and elongates the corresponding ND6 protein by three additional amino acids, Trp-Leu-Trp. The phylogenetic analysis based on mt genomes of sea urchins and related echinoderm groups from GenBank has shown the S and L ND6 variants as shared among the camarodont sea urchins; the rest of the echinoderms demonstrate the S variant only. The data suggest that the ND6 488A>G substitution can be the first example of the trans-species polymorphism in sea urchins, persisting at least since the time of the Odontophora diversification at the Eocene/Oligocene boundary (approximately 34 million years ago), which was characterized by an abrupt climate change and significant global ocean cooling. Alternative hypotheses, including the convergent RNA editing and/or codon reassignment, are not supported by direct comparisons of the ND6 gene sequences with the corresponding transcripts using the basic local alignment search tool (BLAST) of full sea urchin transcriptomes.

Highlights

The data suggest that the ND6 488A>G substitution can be the first example of the trans-species polymorphism in sea urchins, persisting at least since the time of the Odontophora diversification at the Eocene/Oligocene boundary, which was characterized by an abrupt climate change and significant global ocean cooling
Interspecies crosses between S. intermedius and M. nudus have been successfully performed in a laboratory [9,10], which is not unusual for sea urchins
The complete mt genomes and separate ND6 gene sequences of sea urchins and other echinoderm groups, obtained from GenBank, were analyzed to clarify the ND6 L/S polymorphism detected in S. intermedius

Summary

Introduction

The two putative variants share the amino acid residues 1–162 but have different C-terminal ends depending on the removal or not of a three-amino acid tail, Trp-Leu-Trp. In the current study, the complete mt genomes and separate ND6 gene sequences of sea urchins and other echinoderm groups, obtained from GenBank, were analyzed to clarify the ND6 L/S polymorphism detected in S. intermedius. The nucleotide elongation encodes an identical Trp-Leu-Trp C-terminal tail of the ND6 L variant for both sea urchin species (Figure 1).

Results

Conclusion