Characterization of the ribosomal DNA from Trichinella spiralis

Genes and genomes of parasitic nematodes

Our knowledge of gene and genome organization in nematodes is growing rapidly, partly as a result of the Caenorhabditis elegans genome project. Here Martin Hammond and Ted Bianco review what is known about the organization of genes and genomes in parasitic nematode species, using information gained from molecular and cytological approaches. They suggest that there are implications not only for a wide range of problems in parasitology but also for our understanding of genome evolution in eukaryotes.

Genetic diversity within the genus Trichinella as shown by cleavage fragment length polymorphism analysis

The genetic diversity within the genus Trichinella was studied using cleavage fragment length polymorphism (CFLP) analysis. The CFLP method generates specific fingerprints based on single nucleotide mutations. By this method the amplified intergenic regions of the 5S rRNA genes of the eight different genotypes of Trichinella were analysed. The CFLP pattern of T. spiralis was completely different compared with the sylvatic species T. britovi, T. nativa, T. nelsoni, and the genotypes Trichinella T5, Trichinella T6 and Trichinella T8. The T. pseudospiralis intergenic region can be differentiated by size from the other species of Trichinella.

PCR-RFLP patterns of four isolates of Trichinella for rDNA ITS1 region

We have studied the genetic differences among four isolates of Trichinella including a new strain of Trichinella spiralis (ISS 623) recently found from a human case who took a badger in Korea. Because they have a different host origin and came from geographically separated regions, we supposed the genetic pattern of the isolates might be different as had been previously reported. It was analysed by PCR-RFLP analysis of the rDNA repeat that can readily distinguish a species or strain from others. Isolated genomic DNA of each isolate of Trichinella larvae was amplified with ITS1 specific primers and digested with restriction endonucleases. The PCR product of ITS1 was confirmed using Southern blot analysis to be a 910 bp fragment. The restriction fragments of each isolate had variable patterns when it was digested with Rsa 1 only. According to the RFLP patterns, the estimated genetic divergence between each isolate was different. In conclusion, four isolates of Trichinella including a new strain of T. spiralis obtained from a Korean patient may have genetic differences in the ITS1 region and the Shanghai isolate was genetically more similar to the Japanese unknown isolate than others in the ITS1 region.

Detection and identification of eight Trichinella genotypes by reverse line blot hybridization

A reverse line blot (RLB) assay was developed to identify different Trichinella genotypes. The RLB assay accomplishes detection and specific identification of the different Trichinella genotypes and relies on hybridization of the amplified 5S ribosomal DNA intergenic spacer regions to specific, membrane-bound oligonucleotide probes. After one single amplification, we were able to detect and genetically identify six sibling species, i.e., T. spiralis, T. britovi, T. nativa, T. murrelli, T. nelsoni, and T. pseudospiralis, and two additional Trichinella genotypes, T6 and T8. Twenty-four Trichinella strains of different genotypes were unequivocally identified evaluated using one simple PCR-based assay based on single larvae. This assay allows the specific identification of Trichinella species without the need to passage larvae in laboratory animals.

The systematics of the genus Trichinella with a key to species

The authors review the major biological, biochemical, and molecular characters that are used to distinguish the seven Trichinella species (T. spiralis, T. nativa, T. britovi, T. pseudospiralis, T. murrelli, T. nelsoni, T. papuae) and three genotypes whose taxonomic status is yet uncertain (T-6, T-8, T-9). A comparison of host specificity, morphology, reproductive abilities, nurse cell development and freeze resistance is presented, along with useful biochemical and molecular markers. Finally, this information is used to construct a diagnostic key for the species. A phylogenetic classification of the species is needed.

PCR-SSCP of rDNA for the identification of Trichinella isolates from mainland china

A polymerase chain reaction (PCR)-based single strand conformation polymorphism (SSCP) analysis of the expansion segment 5 (domain IV) of the large subunit of ribosomal DNA was employed to characterize seven isolates of Trichinella from China (A-G), including six of pig origin from regions in Dengxian (A), Tianjin (B), Harbin (D), Baoshan (E), Xinye (F) and Xian (G), and one of canine origin from Changchun (C). Isolates A, D, E, F and G were classified as Trichinella spiralis based on SSCP patterns, while the patterns for isolates B and C were consistent with those of Trichinella nativa or Trichinella T6. The results were supported by random amplified polymorphic DNA (RAPD) analysis using five decamer primers and were in accordance with ecological information for the isolates. Single strand conformation polymorphism results also allowed the direct display of mutational sequence variation in the expansion segment among the five isolates of T. spiralis from China, indicating its usefulness for studying population variation within that species.

The identification and characterization of a break within the large subunit ribosomal RNA of Trichinella spiralis: comparison of gap sequences within the genus

A break was identified in the large subunit ribosomal RNA of Trichinella spiralis that results in its dissociation into 2 smaller fragments of approximately equal length. The approximate location of the break within the encoding gene was mapped from subcloned rDNA fragments by S1 protection experiments. The boundaries of the break were determined by cDNA primer extension and S1 nuclease protection assays. The excised fragment (gap sequence) was localized to expansion segment 5 within domain IV from which 86 bases are removed during the excision process. The gap region is flanked by the consensus sequence CGAAAG; however, comparison of expansion segment 5 sequences from T. spiralis, T. nativa, T. nelsoni and T. pseudospiralis, all of which undergo 'gap processing', demonstrates significant size and sequence heterogeneity and provides little evidence for additional consensus sequences which could be implicated in gap processing.

Cloning and characterization of the ribosomal RNA gene repeat from Ostertagia ostertagi

Clones of the rRNA genes of Ostertagia ostertagi were selected from a library prepared from the genomic DNA of adult worms of strain LA-2. A 13.4-kb insert in a clone, lambda OOR78, is comprised of one complete 7.5-kb rDNA unit and portions of two adjacent units. The rDNA unit is directly repeated in a head-to-tail fashion and represents approximately 0.9% of the total genomic DNA. This repeating unit appears to be the only long tandemly repeated sequence in the genome. Restriction enzyme recognition sites in the rDNAs of four strains of O. ostertagi were fully conserved with the exception of one PstI site present in the large rRNA gene which was absent from a proportion of the genes of the LA-2 strain. The rDNA of O. ostertagi is more similar to that of Caenorhabditis elegans in unit length and arrangement than to parasitic helminths previously examined.