Two groups (Paper #1 and Paper #2) report in the October issue of Nature Genetics on the sequencing and analysis of most of the genes found in two of the parasites that cause schistosomiasis, a significant cause of morbidity and mortality in the developing world. The initial analysis of the protein-coding portion of these genomes has shed light on their evolution and physiology, and promises to be an important public resource for the development of new vaccines and drugs to prevent and treat the disease.
Ze-Guang Han and colleagues at the Chinese National Human Genome Center in Shanghai led a team that sequenced and annotated over 13,000 genes that are known to be expressed in Schistosoma japonicum, the parasite that causes schistosomiasis in China and other Asian countries [paper 1]. S. japonicum has a total of approximately 15,000 genes. Sergio Verjovski-Almeida and colleagues at the University of São Paulo sequenced and analyzed 92% of the estimated 14,000 genes of Schistosoma mansoni, which is endemic to Africa, the Caribbean and South America [paper 2].
Of the expressed sequences identified in S. japonicum, 35% shared no similarity with known genes, and 75% had not been reported previously in schistosomes. Of those genes that could be classified, Han and colleagues found that they encode proteins similar to mammalian receptors for insulin, progesterone and neuropeptides, as well as factors that could contribute to the ability of the parasite to evade the host’s immune system. The analysis of S. mansoni gene sequences by Verjovski-Almeida et al. identified factors that are likely involved in its development, tissue structure, motility, nervous system, intracellular signaling, sexual maturation, longevity, and evasion of host immune responses.
Schistosomes are flatworms that live in fresh water, and their larvae directly penetrate human skin to accomplish infection. Those most vulnerable to infection include school-age children, who are exposed when swimming or playing in water, and adults in certain occupations, such as fishermen and irrigation workers. Schistosome infection tends to exacerbate malnutrition and anemia, and long-term consequences include liver fibrosis, bladder cancer and kidney failure. Treatment for schistosomiasis depends on the drug praziquantel, which is effective, although there are concerns about the emergence of drug-resistant parasites. An effective vaccine for humans does not yet exist.
Chinese National Human Genome Center, Shanghai, China
Tel: +86 21 50801325
Paul J. Brindley
Co-author, Tulane University Health Sciences Center, New Orleans, LA, USA
Tel: +1 504 988 4645
University of Sao Paulo, Brazil
Tel: +55 11 3091 2173
(C) Nature Genetics press release.
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