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Isolation and characterization of a termite transferrin gene up-regulated on infection

Authors


G. J. Thompson, Department of Biological Science, Simon Fraser University, 8888 University Drive, Burnaby BC Canada V5S 1S6. Tel.: +1 604 291 5625; Fax: +1 604 291 3496; E-mail: gjt@sfu.ca

Abstract

PCR-based subtractive hybridization was used to isolate genes preferentially expressed in a termite (Mastotermes darwiniensis) following exposure to an entomopathogenic fungus. The subtraction procedure yielded a cDNA clone encoding a putative transferrin that, when sequenced to its ends, is the largest (728 amino acids) for any insect transferrin characterized to date. Cysteines and residues comprising putative iron-binding sites are conserved in both N- and C-terminal lobes, suggesting structural and functional similarity to diferric vertebrate transferrins. A quantitative PCR assay confirmed a significant increase in transferrin expression following infection, suggesting its up-regulation is part of the innate immune response. However, codon-based tests for selection among known insect transferrins revealed only a small proportion of codon-sites positively selected. Thus, unlike certain vertebrate transferrin lineages, no widespread evidence for pathogen-mediated positive selection was detected at this locus.

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