Identification of the Boudicca and Sinbad retrotransposons in the genome of the human blood fluke Schistosoma haematobium

Abstract

Schistosomes have a comparatively large genome, estimated for Schistosoma mansoni to be about 270 megabase pairs (haploid genome). Recent findings have shown that mobile genetic elements constitute significant proportions of the genomes of S. mansoni and S. japonicum. Much less information is available on the genome of the third major human schistosome, S. haematobium. In order to investigate the possible evolutionary origins of the S. mansoni long terminal repeat retrotransposons Boudicca and Sinbad, several genomes were searched by Southern blot for the presence of these retrotransposons. These included three species of schistosomes, S. mansoni, S. japonicum, and S. haematobium, and three related platyhelminth genomes, the liver flukes Fasciola hepatica and Fascioloides magna and the planarian, Dugesia dorotocephala. In addition, Homo sapiens and three snail host genomes, Biomphalaria glabrata, Oncomelania hupensis, and Bulinus truncatus, were examined for possible indications of a horizontal origin for these retrotransposons. Southern hybridization analysis indicated that both Boudicca and Sinbad were present in the genome of S. haematobium. Furthermore, low stringency Southern hybridization analyses suggested that a Boudicca-like retrotransposon was present in the genome of B. truncatus, the snail host of S. haematobium.Key words: schistosome -long terminal report retrotransposon -mobile genetic element -reverse transcriptase -BulinusThe life cycle of schistosomes, diecious trematodes of the order Digenea, involves parasitism of both humans and genera of aquatic or amphibious snails specific to each species: Biomphalaria for Schistosoma mansoni, Oncomelania for S. japonicum, and Bulinus for S. haematobium. In the case of S. mansoni and S. japonicum, adult worms inhabit the portal system blood vessels and mesenteric veins of the intestines of their human hosts. Much progress has been made toward sequencing and sequence annotation of the genomes of S. mansoni and S. japonicum (El-Sayed et al. 2004), including characterization of much of their transcriptomes (Hu et al. 2003, Verjovski-Almeida et al. 2003, and the construction of a bacterial artificial chromosome (BAC) library representing an eight-fold coverage of the S. mansoni genome (Le Paslier et al. 2000). In contrast to the burgeoning wealth of sequence information for S. mansoni and S. japonicum, relatively little is known about the genome sequence of S. haematobium; less than seventy S. haematobium nucleotide sequences were present in S. haematobium by physical measurement (Hilyer 1974, Rollinson et al. 1997) and their chromosomal karyotypes are similar in appearance .Mobile genetic elements (MGEs) represent a major force driving the evolution of eukaryotic genomes (Charlesworth et al. 1994, Kidwell & Lisch 1997, Kazazian 2004 and play an important role in the establishment of genome size (Petrov et al. 2000). In schistosomes, more than half of the genome appears to be composed of, or derived from, repetitive sequences, to a large extent from retrotrans...

Combination of de novo assembly of massive sequencing reads with classical repeat prediction improves identification of repetitive sequences in Schistosoma mansoni

“…Over the last 30 years, roughly a dozen repetitive sequences have been identified by classical molecular biology methods e.g. (Copeland et al, 2003;Copeland et al, 2006). When the genome sequence became available, conventional repeat prediction programs were used to identify additional repetitive sequences.…”

Both sense and antisense strands of the LTR of the Schistosoma mansoni Pao-like retrotransposon Sinbad drive luciferase expression

“…Alternatively, the failure of the Boudicca LTR to drive luciferase activity in HeLa could indicate that either the LTR may not be active in heterologous (mammalian) cells and/or that it cannot drive transcription from the WreXy luciferase gene. Interestingly, the LTR of the same copy of Boudicca examined here can drive green Xuorescent protein (GFP) expression in adult schistosomes transfected by particle bombardment (B. H. Kalinna, personal communication), a Wnding that suggests that the absence of luciferase activity in HeLa cells could reXect tissue speciWcity, perhaps schistosome or molluscan tissue speciWcity, rather than simple lack of promotor function [Boudicca-like retrotransposons may be present in the genomes of some snail hosts of schistosomes, but do not appear to be present in the human genome (Copeland et al 2006)]. Further experiments using whole schistosomes or cell lines such as Bge, a line derived from embryonic Biomphalaria glabrata snail cells (Yoshino et al 1998), may help to clarify whether the Boudicca LTR is capable of functioning in nonhuman tissues.…”