Schistosomiasis Research Group

The genome of Schistosoma mansoni, at 270Mb, is large compared to the majority of pathogens that have already been sequenced.  As a result, it has been difficult for the community to raise funds for the sequencing of the full genome.  Some initial moves were made with the construction of two BAC libraries containing genomic inserts.  The ends of most of the clones in these libraries were sequenced, and both TIGR in the USA and the Sanger Institute undertook pilot projects to sequence complete BACs and to determine whether a BAC-by-BAC "map-as-you-go" approach would be feasible.  Both centres reached the same conclusion: the presence of large amounts of repeat sequence in the genomes (estimated at 40%) effectively ruled out this option.  The only remaining possibility was to raise funds for a "whole genome shotgun" (WGS) approach, with the possibility of adding additional mapping data as an when time and resources allowed.

Funding was obtained by TIGR from the NIH and by the Sanger Institute via the Pathogen Sequencing Advisory Group, and WGS sequencing begin in 2003.  The two centres have produced >2.5 billion bases of sequence, representing >9X coverage of the genome.  As at the end of March 2004, assembly of the genome sequence is underway, and both of the sequencing centres will be undertaking an initial round of annotation and gene finding, with a view to publishing the full genome sequence at the earliest opportunity.  After that, the genome database will be made available to the community, and it is hoped that database will be actively maintained.

In parallel, the genome sequence of the related species S. japonicum is also being sequenced by the Chinese National Human Genome Center in Shanghai.  Having the full sequences of both genomes will allow many important analyses to be performed, and should improve the quality of the gene prediction in both species.  Although no agreement on data sharing has yet been reached, it would seem the most sensible option to combine both genomes into a single database resource.

A diagram of the karyotype of S. mansoni showing the C-banding pattern which stains the heterochromatic regions of the chromosomes.