Site-specific reverse splicing of a HEG-containing group I intron in ribosomal RNA

The wide, but scattered distribution of group I introns in nature is a result of two processes; the vertical inheritance of introns with or without losses, and the occasional transfer of introns across species barriers. Reversal of the group I intron self-splicing reaction, termed reverse splicing, coupled with reverse transcription and genomic integration potentially mediate an RNA-based intron mobility pathway. Compared to the well characterized endonuclease-mediated intron homing, reverse splicing is less specific and represents a likely explanation for many intron transpositions into new genomic sites. However, the frequency and general role of an RNA-based mobility pathway in the spread of natural group I introns is still unclear. We have used the twin-ribozyme intron (Dir.S956-1) from the myxomycete Didymium iridis to test how a mobile group I intron containing a homing endonuclease gene (HEG) selects between potential insertion sites in the small subunit (SSU) rRNA in vitro, in Escherichia coli and in yeast. Surprisingly, the results show a site-specific RNA-based targeting of Dir.S956-1 into its natural (S956) SSU rRNA site. Our results suggest that reverse splicing, in addition to the established endonuclease-mediated homing mechanism, potentially accounts for group I intron spread into the homologous sites of different strains and species

A mitogenomic approach to the taxonomy of pollocks: Theragra chalcogramma and T. finnmarchica represent one single species

<p>Abstract</p> <p>Background</p> <p>The walleye pollock (<it>Theragra chalcogramma</it>) and Norwegian pollock (<it>T. finnmarchica</it>) are confined to the North Pacific and North Atlantic Oceans, respectively, and considered as distinct species within the family Gadidae. We have determined the complete mtDNA nucleotide sequence of two specimens of Norwegian pollock and compared the sequences to that of 10 specimens of walleye pollock representing stocks from the Sea of Japan and the Bering Sea, 2 specimens of Atlantic cod (<it>Gadus morhua</it>), and 2 specimens of haddock (<it>Melanogrammus aeglefinus</it>).</p> <p>Results</p> <p>A total number of 204 variable positions were identified among the 12 pollock specimens, but no specific substitution pattern could be identified between the walleye and Norwegian pollocks. Phylogenetic analysis using 16.500 homologous mtDNA nucleotide positions clearly identify the Norwegian pollock within the walleye pollock species cluster. Furthermore, the Norwegian pollock sequences were most similar to mitochondrial genotypes present in walleye pollock specimens from the Sea of Japan, an observation supported both by neighbor-joining, maximum parsimony, and maximum likelihood analyses.</p> <p>Conclusion</p> <p>We infer that walleye pollock and Norwegian pollock represent one single species and that Norwegian pollock has been recently introduced from the Pacific to the Atlantic Oceans.</p

Characterization of mitochondrial mRNAs in codfish reveals unique features compared to mammals

Expression and processing of mitochondrial gene transcripts are fundamental to mitochondrial function, but information from early vertebrates like teleost fishes is essentially lacking. We have analyzed mitogenome sequences of ten codfishes (family Gadidae), and provide complete sequences from three new species (Saithe, Pollack and Blue whiting). Characterization of the mitochondrial mRNAs in Saithe and Atlantic cod identified a set of ten poly(A) transcripts, and six UAA stop codons are generated by posttranscriptional polyadenylation. Structural assessment of poly(A) sites is consistent with an RNaseP cleavage activity 5′ of tRNA acceptor-like stems. COI, ND5 and ND6 mRNAs were found to harbor 3′ UTRs with antisense potential extending into neighboring gene regions. While the 3′ UTR of COI mRNA is complementary to the tRNASer (UCN) and highly similar to that detected in human mitochondria, the ND5 and ND6 3′ UTRs appear more heterogenic. Deep sequencing confirms expression of all mitochondrial mRNAs and rRNAs, and provides information about the precise 5′ ends in mature transcripts. Our study supports an overall evolutionary conservation in mitochondrial RNA processing events among vertebrates, but reveals some unique 5′ and 3′ end characteristics in codfish mRNAs with implications to antisense regulation of gene expression

MicroRNAs in Daphnia magna identified and characterized by deep sequencing, genome mapping and manual curation

MicroRNAs (miRNAs) are small non-coding RNAs that function in RNA silencing and post-transcriptional regulation of gene expression in most organisms. The water flea, Daphnia magna is a key model to study phenotypic, physiological and genomic responses to environmental cues and miRNAs can potentially mediate these responses. By using deep sequencing, genome mapping and manual curations, we have characterised the miRNAome of D. magna. We identified 66 conserved miRNAs and 13 novel miRNAs; all of these were found in the three studied life stages of D. magna (juveniles, subadults, adults), but with variation in expression levels between stages. Forty-one of the miRNAs were clustered into 13 genome clusters also present in the D. pulex genome. Most miRNAs contained sequence variants (isomiRs). The highest expressed isomiRs were 3′ template variants with one nucleotide deletion or 3′ non-template variants with addition of A or U at the 3′ end. We also identified offset RNAs (moRs) and loop RNAs (loRs). Our work extends the base for further work on all species (miRNA, isomiRs, moRNAs, loRNAs) of the miRNAome of Daphnia as biomarkers in response to chemical substances and environment cues, and underline age dependency

MicroRNAs in Daphnia magna identified and characterized by deep sequencing, genome mapping and manual curation

MicroRNAs (miRNAs) are small non-coding RNAs that function in RNA silencing and post-transcriptional regulation of gene expression in most organisms. The water flea, Daphnia magna is a key model to study phenotypic, physiological and genomic responses to environmental cues and miRNAs can potentially mediate these responses. By using deep sequencing, genome mapping and manual curations, we have characterised the miRNAome of D. magna. We identified 66 conserved miRNAs and 13 novel miRNAs; all of these were found in the three studied life stages of D. magna (juveniles, subadults, adults), but with variation in expression levels between stages. Forty-one of the miRNAs were clustered into 13 genome clusters also present in the D. pulex genome. Most miRNAs contained sequence variants (isomiRs). The highest expressed isomiRs were 3′ template variants with one nucleotide deletion or 3′ non-template variants with addition of A or U at the 3′ end. We also identified offset RNAs (moRs) and loop RNAs (loRs). Our work extends the base for further work on all species (miRNA, isomiRs, moRNAs, loRNAs) of the miRNAome of Daphnia as biomarkers in response to chemical substances and environment cues, and underline age dependency

MicroRNAs as Potential Biomarkers in Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare and aggressive type of skin cancer associated with a poor prognosis. This carcinoma was named after its presumed cell of origin, the Merkel cell, which is a mechanoreceptor cell located in the basal epidermal layer of the skin. Merkel cell polyomavirus seems to be the major causal factor for MCC because approximately 80% of all MCCs are positive for viral DNAs. UV exposure is the predominant etiological factor for virus-negative MCCs. Intracellular microRNA analysis between virus-positive and virus-negative MCC cell lines and tumor samples have identified differentially expressed microRNAs. Comparative microRNA profiling has also been performed between MCCs and other non-MCC tumors, but not between normal Merkel cells and malignant Merkel cells. Finally, Merkel cell polyomavirus encodes one microRNA, but its expression in virus-positive MCCs is low, or non-detectable or absent, jeopardizing its biological relevance in tumorigenesis. Here, we review the results of microRNA studies in MCCs and discuss the potential application of microRNAs as biomarkers for the diagnosis, progression and prognosis, and treatment of MCC

A mitogenomic approach to the taxonomy of pollocks: and represent one single species-0

<p><b>Copyright information:</b></p><p>Taken from "A mitogenomic approach to the taxonomy of pollocks: and represent one single species"</p><p>BMC Evolutionary Biology 2007;7():86-86.</p><p>Published online 7 Jun 2007</p><p>PMCID:PMC1894972.</p><p></p>genes (indicated by the standard one-letter symbols for amino acid below the diagram), are encoded by the H-strand. Abbreviations: SSU and LSU, mitochondrial small- and large-subunit ribosomal RNA genes; ND1-6, NADH dehydrogenase subunit 1 to 6; COI-III, cytochrome c oxidase subunit I to III; A6 and A8, ATPase subunit 6 and 8; Cyt b, cytochrome b; OH and OL, origin of H-strand and L-strand replication; CR, control region containing the D-loop. () Distribution of variable sites in pollock mtDNA numbered according to the sequence of the Norwegian pollock Tf 19 (AM489718, Table 1). The position 834+ in SSU rDNA indicates nucleotide insertion between positions 834 and 835 in Tf 19. The variable sites were aligned to that of Tf 19. Identical sites are indicated by dots and deletions by dashes. The proposed diagnostic single nucleotide polymorphism at ND4 of Sea of Japan and Bering Sea pollocks [14] is boxed at position 11578