Evolution of the Antarctic teleost immunoglobulin heavy chain gene

Antarctic teleost immunoglobulins: More extreme, more interesting

“…The elongation of the EMPD was generated by the insertion of 13-aa tandem repeats, that were encoded by 39-nt additional exons, present in various numbers (up to 4) according to the species analyzed. Analysis of the EMPD amino acid composition showed quite abundant negatively charged residues (aspartic and glutamic acid, 23.7%), and cysteine and proline residues being 6.2 and 4.2% of the total, respectively [41].…”

“…It consisted in a large insertion in the Igm gene locus in parallel with a significant modification of the mRNA splicing mechanism resulting in a membrane antigen receptor of only two constant Ig domains [41]. This event occurred during the major cooling period, and, thus, may have an adaptive key significance.…”

“…We were thus prompted to elucidate the different splicing mechanisms observed. Genomic DNA analyses were performed in two Antarctic species, C. hamatus and C. mawsoni, and in one non-Antarctic notothenioid, B. diacanthus [41]. While the non-Antarctic species sequence did not show any peculiar feature, those from the Antarctic species revealed that each 39-nt additional exon fell within a 411-nt long sequence that was the reverse complement sequence of an upstream region beginning in the CH2eCH3 intron, and ending in the region located between the CH2eCH3 intron and the 3 0 UTR.…”

“…The results showed the formation of a long duplex, due to the presence of complementary reverse sequences, stabilized by free energy of À3835.10 kcal/mol at the Antarctic physiological temperature of 0 C. Since the CH3 exon 5 0 splice site and the RC 39-nt region 3 0 splice site are included in this duplex, they are not available to bind the spliceosomal complex [41]. Nineteen out of 20 substitutions in RB and RA were found to be non-synonymous, and 5 substitutions introduced a cysteine codon.…”

“…The consensus sequence DKLGALCPCHIRD of the 13-aa repeats of all the Antarctic species sequenced showed a clearly symmetrical hydropathic character. Therefore, the assembly of several repeats gives rise to a region consisting of alternate hydrophilic and hydrophobic parts [41].…”