The mitochondrial genome of Ixodes ricinus reveals Tick-Box: a motif involved in 3'-end formation of mitochondrial transcripts and conserved in ticks, basal chelicerates plus Drosophila
The mitochondrial genome of Ixodes ricinus reveals Tick-Box: a motif involved in 3'-end formation of mitochondrial transcripts and conserved in ticks, basal chelicerates plus Drosophila
Sunday, November 10, 2013: 3:30 PM
Meeting Room 6 A (Austin Convention Center)
The typical bilaterian mitochondrial DNA (hereafter mtDNA) is a circular molecule of 14-18 kb
encoding for 37 genes (i.e. 13 protein subunits of the respiratory complexes; 22 tRNAs and 2 rRNAs
of mt translational apparatus) involved in the mitochondrial metabolism. According to the tRNA
punctuation model, the metazoan mitochondrial genome is transcribed as large polycistronic
precursors that are maturated by endonucleolytic cleavage at tRNA borders and RNA polyadenylation.
Among arthropods, the mtDNA has been completely sequences in more then five hundreds different
species (http://www.caspur.it/mitozoa), mainly Hexapoda, while within ticks, complete mt genome
sequences is available only for 11 species. Moreover, the mt genome has not yet been determined for
the main vector of Lyme borreliosis in Europe, the widespread sheep tick Ixodes ricinus.
We have recently been determined in our laboratories the mtDNA of Ixodes ricinus. Starting from this
genome and using a combination of mitogenomics and transcriptional analyses (i.e. EST analysis -
Expressed Sequence Tag, and 3' RACE - Random Amplification of cDNA End), we found that in all
currently sequenced tick lineages (Prostriata, Metastriata and Argasidae) the 3'-end of the
polyadenylated nad1 and rrnL transcripts do not follow the tRNA punctuation model and is located
upstream of a degenerate 17-bp DNA motif, named by us "Tick-Box". A slightly different motif is
also present downstream the 3'-end of nad1 transcripts in the primitive chelicerate L. polyphemus and
Diptera of the genus Drosophila, indicating the ancient origin and the evolutionary conservation of
this motif in arthropods. The transcriptional analyses suggest that this motif directs the 3'-end
formation of the nad1/rrnL mature RNAs, likely working as a transcription termination signal or a
processing signal of precursor transcripts that is either un-transcribed or quickly removed from the
primary precursor transcripts of nad1 and rrnL., According to the proposed role, as most regulatory
elements, the Tick-Box motif is characterized by a taxon-specific evolution.
encoding for 37 genes (i.e. 13 protein subunits of the respiratory complexes; 22 tRNAs and 2 rRNAs
of mt translational apparatus) involved in the mitochondrial metabolism. According to the tRNA
punctuation model, the metazoan mitochondrial genome is transcribed as large polycistronic
precursors that are maturated by endonucleolytic cleavage at tRNA borders and RNA polyadenylation.
Among arthropods, the mtDNA has been completely sequences in more then five hundreds different
species (http://www.caspur.it/mitozoa), mainly Hexapoda, while within ticks, complete mt genome
sequences is available only for 11 species. Moreover, the mt genome has not yet been determined for
the main vector of Lyme borreliosis in Europe, the widespread sheep tick Ixodes ricinus.
We have recently been determined in our laboratories the mtDNA of Ixodes ricinus. Starting from this
genome and using a combination of mitogenomics and transcriptional analyses (i.e. EST analysis -
Expressed Sequence Tag, and 3' RACE - Random Amplification of cDNA End), we found that in all
currently sequenced tick lineages (Prostriata, Metastriata and Argasidae) the 3'-end of the
polyadenylated nad1 and rrnL transcripts do not follow the tRNA punctuation model and is located
upstream of a degenerate 17-bp DNA motif, named by us "Tick-Box". A slightly different motif is
also present downstream the 3'-end of nad1 transcripts in the primitive chelicerate L. polyphemus and
Diptera of the genus Drosophila, indicating the ancient origin and the evolutionary conservation of
this motif in arthropods. The transcriptional analyses suggest that this motif directs the 3'-end
formation of the nad1/rrnL mature RNAs, likely working as a transcription termination signal or a
processing signal of precursor transcripts that is either un-transcribed or quickly removed from the
primary precursor transcripts of nad1 and rrnL., According to the proposed role, as most regulatory
elements, the Tick-Box motif is characterized by a taxon-specific evolution.
