Differential gene expression in haemocytes of the snail Biomphalaria glabrata: effects of Schistosoma mansoni infection.

Parasite encapsulation and destruction in Biomphalaria glabrata has been shown to involve the cellular component of the snail's internal defence system, the haemocytes. To identify genes involved in the immunobiology of these cells, we used the method of differential display reverse transcriptase polymerase chain reaction (DDRT-PCR) to investigate differential gene regulation in haemocytes isolated from Schistosoma mansoni exposed and unexposed snails. RNA isolated from circulating haemocytes from resistant snails (BS-90 stock), previously exposed to S. mansoni, was analysed using 12 different arbitrary primers in conjunction with an anchored Oligo d(T(11)CG) primer. Transcription profiles between haemocytes of parasite exposed and unexposed snails were compared and a total of 87 differentially regulated bands were identified and isolated. Of these, 65 bands were cloned and used as probes in Southern blots to show the presence of corresponding sequences in the snail genome. RT-PCR was performed to verify the regulation of these transcripts. DNA sequence analysis showed that the majority of the cloned sequences were novel, although a few showed a high degree of sequence similarity to other sequences in the DNA and protein databases. One of these included a differentially expressed transcript that showed a significant degree of sequence identity to E. coli transposase Tn5, an enzyme whose activity is normally associated with generating mobility and instability in the genome.