Non-random organization of the Biomphalaria glabrata genome in interphase Bge cells and the spatial repositioning of activated genes in cells co-cultured with Schistosoma mansoni

Abstract

The snail, Biomphalaria glabrata is a major intermediate host for the parasitic trematode Schistosoma mansoni the causative agent of human schistosomiasis. Efforts are underway to decipher the molecular basis of the snail - host schistosome interaction, and the Bge embryonic cell line derived from this snail provides a unique in vitro model cell system to assess whether interactions between the snail host and parasite affects the cell and genome biology for both organisms. In line with these interests, this snail has been chosen as a molluscan representative to have its genome sequenced. By using the method whereby labelled nucleotides are incorporated into replicating DNA and cells are then allowed to progress through several cell divisions in the absence of labelled nucleotides we were able to visualise, for the first time, whole individual chromosomes within interphase nuclei of the Bge cells, study their morphology and where they are located within interphase nuclei. By using bioimaging and image analysis we revealed that these chromosome territories are similar in morphology to those found in more complex organisms and are radially positioned within nuclei, non-randomly. Furthermore, specific gene loci, present as 2 copies on homologous Bge chromosomes, delineated using BAC probes and fluorescence in situ hybridisation (FISH), were also non-randomly positioned with Bge cell nuclei. In order to determine whether there is a genomic response to parasitic exposure, the interphase spatial positioning of the gene loci was assessed after co-culturing live or irradiated attenuated schistosoma miracidia with the Bge cells for 30 minutes to 24 hours. The genes investigated, actin and ferritin, are genes known to be up-regulated in the snail host when subjected to parasite infection. Most interestingly, with alteration in the expression of these genes, as determined by quantitative-PCR, gene repositioning in interphase nuclei was correlated temporally with up-regulation of gene expression and then with down-regulation. Co-culture with irradiated attenuated parasite did not elicit interphase gene repositioning correlated with changes in gene expression. Thus, the parasite is able to elicit influence directly over the host genome via secreted molecules through the hosts’ own nuclear architecture.