Trichinella pseudospiralis vs. T. spiralis thymidylate synthase gene structure and T. pseudospiralis thymidylate synthase retrogene sequence.
BACKGROUND
Thymidylate synthase is a housekeeping gene, designated ancient due to its role in DNA synthesis and ubiquitous phyletic distribution. The genomic sequences were characterized coding for thymidylate synthase in two species of the genus Trichinella, an encapsulating T. spiralis and a non-encapsulating T. pseudospiralis.


METHODS
Based on the sequence of parasitic nematode Trichinella spiralis thymidylate synthase cDNA, PCR techniques were employed.


RESULTS
Each of the respective gene structures encompassed 6 exons and 5 introns located in conserved sites. Comparison with the corresponding gene structures of other eukaryotic species revealed lack of common introns that would be shared among selected fungi, nematodes, mammals and plants. The two deduced amino acid sequences were 96% identical. In addition to the thymidylate synthase gene, the intron-less retrocopy, i.e. a processed pseudogene, with sequence identical to the T. spiralis gene coding region, was found to be present within the T. pseudospiralis genome. This pseudogene, instead of the gene, was confirmed by RT-PCR to be expressed in the parasite muscle larvae.


CONCLUSIONS
Intron load, as well as distribution of exon and intron phases in thymidylate synthase genes from various sources, point against the theory of gene assembly by the primordial exon shuffling and support the theory of evolutionary late intron insertion into spliceosomal genes. Thymidylate synthase pseudogene expressed in T. pseudospiralis muscle larvae is designated a retrogene.
Elżbieta
E
Jagielska
Andrzej
A
Płucienniczak
Magdalena
M
Dąbrowska
Anna
A
Dowierciał
Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02-093 Warszawa, Poland. w.rode@nencki.gov.pl.
Wojciech
W
Rode
D000818:Animals; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D007814:Larva / Q000201:enzymology / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D013045:Species Specificity; D013940:Thymidylate Synthase / Q000235:genetics / Q000378:metabolism*; D014234:Trichinella / Q000201:enzymology* / Q000235:genetics*
D013940:Thymidylate Synthase