Schistosome albumin is of host, not parasite, origin q Ricardo DeMarco * , William Mathieson, Gary P. Dillon, R. Alan Wilson Department of Biology, University of York, P.O. Box 373, York YO10 5YW, UK Received 14 February 2007; received in revised form 15 March 2007; accepted 19 March 2007 Abstract Recent work has implicated schistosome albumin as part of a mechanism for neutralizing the oxidative assault by host immune defenses and suggested that the gene had been acquired by horizontal transfer from the mammalian host. In the course of proteomic analyses of Schistosoma mansoni adult worm vomitus and eggs recovered from mice, we identified numerous peptides, largely derived from murine rather than parasite albumin. We therefore conjectured that the supposed S. mansoni albumin sequence deposited on Gen- Bank might be the result of contamination rather than horizontal gene transfer. Based on phylogenetic analysis the most likely source was the Syrian (golden) hamster Mesocricetus auratus. Proteomic analysis of Syrian hamster albumin generated peptide identities to S. mansoni as the top hit, with a high ion score >1,500 and 63% coverage of the translated cDNA sequence. RT-PCR using specific primers permitted amplification of the M. auratus albumin transcript, which is identical to the deposited S. mansoni albumin sequence. PCR amplification of a fragment of the M. auratus albumin gene from genomic DNA suggests a homologous structure to the Mus musculus albumin gene. We were unable to find the S. mansoni albumin gene sequence by in silico searching on either version 3 of the S. mansoni genome assembly or the >3 million shotgun DNA reads. Finally, Southern blotting detected the albumin gene in M. auratus but not in S. mansoni genomic DNA, even when the latter was present in a 10-fold excess. Collectively, our data make the strongest case that the schis- tosome albumin protein described in previous reports is of host origin and all nucleotide-derived data are the result of contamination with host material. By analogy, we suggest that other reported examples of horizontal gene transfer to schistosomes might similarly be explained by complementary/genomic DNA contamination. Ó 2007 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Horizontal gene transfer; Proteomics; Polymerase chain reaction; Southern blotting 1. Introduction Schistosoma mansoni is a digenetic platyhelminth trema- tode and one of the causative agents of schistosomiasis in humans. The disease is endemic in 74 developing countries, infecting about 200 million individuals, and it is estimated that an additional 500–600 million are at risk (WHO, 2002). Schistosomes persist in the human host for decades despite eliciting a pronounced immune response (Pearce and MacDonald, 2002) and our knowledge of the mecha- nisms which the parasite uses to evade host defenses is still incomplete. Recently, several groups have claimed that hor- izontal transfer permitted the direct acquisition of host genes that could be co-opted to perform a role in immune evasion (Imase et al., 2003; Inal, 2005; Williams et al., 2006). Albumin is the major protein of human plasma where its main function is to act as a protein carrier for steroids, fatty acids and thyroid hormones; it is also involved in the regulation of plasma osmotic pressure. Sayed et al. (2006) described the novel albumin of the human blood fluke S. mansoni as one of the main oxidised products, detected by mass spectroscopy, after silencing of peroxire- doxins (Prx), the H 2 O 2 – neutralizing enzymes of the para- site. In addition, the expression of the S. mansoni albumin gene was induced when either adult or schistosomula par- asites in axenic culture were exposed to oxidative stress 0020-7519/$30.00 Ó 2007 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijpara.2007.03.004 q Note: Nucleotide sequence data reported in this paper is available in GenBank., EMBL and DDBJ databases under Accession Nos. EF488484 and EF4884845. * Corresponding author. Tel.: +44 1904 328592; fax: +44 1904 328505. E-mail address: rdemarco77@yahoo.com.br (R. DeMarco). www.elsevier.com/locate/ijpara International Journal for Parasitology 37 (2007) 1201–1208