Convergent evolution of antifreeze glycoproteins in Antarctic notothenioid fish and Arctic cod
AUTOR(ES)
Chen, Liangbiao
FONTE
The National Academy of Sciences of the USA
RESUMO
Antarctic notothenioid fishes and several northern cods are phylogenetically distant (in different orders and superorders), yet produce near-identical antifreeze glycoproteins (AFGPs) to survive in their respective freezing environments. AFGPs in both fishes are made as a family of discretely sized polymers composed of a simple glycotripeptide monomeric repeat. Characterizations of the AFGP genes from notothenioids and the Arctic cod show that their AFGPs are both encoded by a family of polyprotein genes, with each gene encoding multiple AFGP molecules linked in tandem by small cleavable spacers. Despite these apparent similarities, detailed analyses of the AFGP gene sequences and substructures provide strong evidence that AFGPs in these two polar fishes in fact evolved independently. First, although Antarctic notothenioid AFGP genes have been shown to originate from a pancreatic trypsinogen, Arctic cod AFGP genes share no sequence identity with the trypsinogen gene, indicating trypsinogen is not the progenitor. Second, the AFGP genes of the two fish have different intron–exon organizations and different spacer sequences and, thus, different processing of the polyprotein precursors, consistent with separate genomic origins. Third, the repetitive AFGP tripeptide (Thr-Ala/Pro-Ala) coding sequences are drastically different in the two groups of genes, suggesting that they arose from duplications of two distinct, short ancestral sequences with a different permutation of three codons for the same tripeptide. The molecular evidence for separate ancestry is supported by morphological, paleontological, and paleoclimatic evidence, which collectively indicate that these two polar fishes evolved their respective AFGPs separately and thus arrived at the same AFGPs through convergent evolution.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=20524Documentos Relacionados
- Evolution of antifreeze glycoprotein gene from a trypsinogen gene in Antarctic notothenioid fish
- An antifreeze glycopeptide gene from the antarctic cod Notothenia coriiceps neglecta encodes a polyprotein of high peptide copy number.
- An antifreeze glycopeptide gene from the antarctic cod Notothenia coriiceps neglecta encodes a polyprotein of high peptide copy number.
- Antarctic fish hemoglobins: Evidence for adaptive evolution at subzero temperature
- Diversity and Structure of Bacterial Communities in Arctic versus Antarctic Pack Ice