The immunoglobulin of the Antarctic teleost Trematomus bernacchii was inves
tigated with respect to the amino acid sequence of the heavy chain and the
diversity of the gene segments encoding the variable domain. A cDNA express
ion library was constructed from the spleen and immunoscreened with rabbit
anti-T. bernacchii IgH. A positive clone, found to encode the complete IgH
sequence, including the leader peptide, was sequenced. Comparison of the de
duced amino acid sequence of T. bernacchii constant domains with those from
other actinopterygians showed identities ranging between 53.1 and 71.1%. M
ultiple sequence alignment revealed the pressure of two remarkable insertio
ns occurring in the VH-CH1 switch region and at the CH2-CH3 boundary. Addit
ional differences were found in the number and positions of putative N-glyc
osylation sites as well as of cysteine residues not involved in the intrado
main bridges. An oligonucleotide primer was designed to amplify in PCR cDNA
encoding different variable domains. The nucleotide sequence of 33 VH clon
es was determined, and found distributed over three gene families, named Tr
be VH I, Trbe VH II, and Trbe VH III. Nine distinct JH gene segments were a
lso identified. The differences found with respect to other fish Ig, as wel
l as the low diversity found in VH genes, were attributed to adaptation pro
cesses.