Differential transcription of two highly divergent gut-expressed Bm86 antigen gene homologues in the tick Rhipicephalus appendiculatus (Acari: Ixodida)

Abstract

The transcriptional control of gene expression is not well documented in the Arthropoda. We describe tran-scriptional analysis of two exceptionally divergent homologues (Ra86) of the Bm86 gut antigen from Rhi-picephalus appendiculatus. Bm86 forms the basis of a commercial vaccine for the control of Rhipicephalus (Boophilus) microplus. The R. appendiculatus Ra86 proteins contain 654 and 693 amino acids, with only 80% amino acid sequence identity. Reverse-transcription PCR of gut cDNA showed transcription of only one genotype in individual female ticks. PCR amplification of 3 untranslated sequences from genomic DNA indicated that both variants could be encoded within a single genome. When both variants were present, one of the two Ra86 genotypes was transcriptionally dominant.