SEQUENCE-ANALYSIS OF A GENE FAMILY ENCODING TAENIA-OVIS VACCINE ANTIGENS EXPRESSED DURING EMBRYOGENESIS OF EGGS

The 45W vaccine antigen of the cestode parasite Taenia ovis is a membe r of a small gene family estimated to comprise six members. All six ge nes were cloned and characterised. Nucleotide sequence analysis of the different family members identified a set of closely related genes ex hibiting between 75.2 and 98.6% DNA sequence homology. Intron/exon str ucture for the various genes constituting the family was found to be c onserved. Open reading frame analysis and pairwise alignments of predi cted polypeptides from the various members of the family revealed that the encoded proteins share between 51.8 and 96.5% amino acid identity with the host-protective 45W antigen. Polymerase chain reaction (PCR) primers were designed which allowed amplification of individual famil y members in a transcript-specific manner. These were used to investig ate gene expression in different developmental stages of the parasite by reverse-transcription polymerase chain reaction (RT-PCR). All membe rs of the gene family were expressed during the T. ovis life-cycle. 45 W gene family transcription correlates with embryogenesis of eggs and expression is increased in activated eggs (oncospheres). One family me mber, ToW3S, was expressed in the early larvae (cysticercus) stages. E xpression of genes closely related to the 45W vaccine antigen has impo rtant implications for immune evasion under selection from the applica tion of a 45W-based vaccine. (C) 1997 Elsevier Science B.V.