Since the discovery that genes are split into intron and exons, the studies of the mechanisms involved in splicing pointed to presence of consensus signals in an attempt to generalize the process for all living cells. However, as discussed in the present review, splicing is a theme full of variations. The trans-splicing of pre-mRNAs, the joining of exons from distinct transcripts, is one of these variations with broad distribution in the phylogenetic tree. The biological meaning of this phenomenon is discussed encompassing reactions resembling a possible noise to mechanisms of gene expression regulation. All of them however, can contribute to the generation of life diversity.Key words: RNA processing -alternative trans-splicing -spliced leader RNA -trypanosomatids -nematodes -mammalian Most of the protein-coding eukaryotic genes display an interrupted structure alternating exons and introns. After transcription, introns must be removed from the primary transcript (pre-mRNA) to generate a translatable mature mRNA. It is interesting to note that the mature mRNA is constituted of 5' and 3' untranslatable regions (UTR) flanking the open reading frame (ORF) and that UTR are also exons. The precise excision of the introns and the joining of neighboring exons is a complex process generally named splicing, and when this processing occurs within a single pre-mRNA molecule it can also be called cis-splicing (Moore et al. 1993, Burge et al. 1999.Cis-splicing occurs in a two-step mechanism, each step consisting of a transesterification reaction (Moore et al. 1993) (Fig. 1A). The spliceosome, a ribonucleoprotein machinery composed of five small ribonucleoproteins (U1, U2, U4, U5, U6 snRNPs, named in relation to the kind of associated RNA molecule) and approximately 300 distinct proteins, is responsible for the splicing catalysis (Burge et al. 1999).Much effort was expended on the comprehension of the structure and dynamics of this complex machine during the splicing process, but the rules that discriminate introns and exons within the message are still poorly understood. Nevertheless, four conserved pre-mRNA sequence elements, which interact with the spliceosome, have been characterized as determinants in the splicing process (Moore et al. 1993, Burge et al. 1999 (Fig. 1C). In mammals, the 5' splice site consensus is AG/GURAGU (R for purine, /for splice site, bold for the dinucleotide 5' intron boundary) while the 3' splice site consensus is YAG/G (Y for pyrimidine, /for splice site, bold for the dinucleotides 3' intron boundary). There is also a conservation of nucleotide sequence around the branch point, CURAY (Y for pyrimidine, R for purine and A for branch Recently, other cis-regulatory elements were implicated in splice site recognition, e.g. the exonic splicing enhancers (ESEs) (Fig. 1C). ESEs are localized within exons and interact with a family of proteins rich in serine and arginine (SR proteins) that recruits the spliceosome to the proximal splice site .Although the presence of those consensuses was observed, it i...

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The addition of a capped mini-exon [spliced leader (SL)

TMZ added to accelerated radiotherapy for GBM resulted in prolonged overall survival with low rates of severe hematological toxicity.

Taking into account the expected increased shortages in PCPs in rural regions, the results show the need for targeted interventions for improving lifestyle counseling in rural practices.

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The identification of new bovine male-specific DNA sequences is of great interest because the bovine Y chromosome remains poorly characterized in terms of physical and genetic maps. Since taurine and zebu Y chromosomes are structurally different, the identification of Y-specific sequences present in both sub-species is particularly important: these sequences are of evolutionary significance and can be broadly used for embryo sexing. In this work, we initially used the random amplified polymorphic DNA (RAPD) technique to search for male-specific sequences present as monomorphic markers in genomic DNA from zebu and taurine bulls. A male-specific RAPD band was found to be present and highly conserved in both sub-species, as demonstrated by Southern blotting, fluorescent in situ hybridization (FISH) and DNA sequencing. In a previous work, a pair of primers derived from this marker was successfully used in taurine and zebu embryo sexing.

Trypanosomatidae is a family of flagellated protozoans. A variety of Trypanosomatidae species from the Leishmania and Trypanosoma genera are responsible for various human diseases that lead to millions of deaths in developing countries. These organisms branch early in the phylogenetic tree and exhibit a single, conserved mechanism for gene expression (Simpson et al. 2006). Protein coding genes are polycistronically transcribed by RNA polymerase II from only a small number of promoter regions and individual nuclear messenger RNA (mRNA) is then generated via two coupled reactions: trans-splicing and polyadenylation (Lebowitz et al. 1993, Mayer & Floeter-Winter 2005. Although transsplicing is a processing event that involves two independently transcribed RNA molecules, spliced leader (SL) RNA and pre-mRNA, the acceptor and donor sequences are identical to those in the majority of cis-spliced transcripts (Liang et al. 2003, Mayer & Floeter-Winter 2005. Trans-splicing processing adds a 39-nt mini-exon (ME) (SL) sequence derived from SL RNA to the 5' end of virtually all mRNAs. The SL RNA donor sites invariably consist of a GU dinucleotide. This processing occurs at transcribed intergenic regions and the acceptor sites are generally composed of an AG dinucleotide preceded by a polypyrimidine tract (Liang et al. 2003, Mayer & Floeter-Winter 2005, Orlando et al. 2007). The polyadenylation of an upstream gene appears to be coupled to the trans-splicing of a second gene that is typically 200-500 nts downstream (Lebowitz et al. 1993, Hug et al. 1994). High-throughput analyses have shown that the locations of both the trans-splicing and the polyadenylation acceptor sites are quite variable in trypanosomatids and a considerable number of alternative sites have been described (Siegel et al. 2011).Until recently, SL addition trans-splicing was exclusively associated with pre-mRNA processing and other RNA molecules were not considered to be involved in this processing mechanism. However, polyadenylation of non-protein coding genes has been detected in both prokaryotes and eukaryotes (Fleischmann et al. 2004). In trypanosomatids, it has been shown that ε ribosomal RNA (rRNA) fragment precursors (the 3'-most portion of the fragmented large rRNA subunit) are polyadenylated in Leishmania (Viannia) braziliensis and Leishmania (Leishmania) donovani (Decuypere et al. 2005). Moreover, in Trypanosoma brucei, a small number of RNA polymerase II-transcribed tRNA sec precursor transcripts have been shown to exhibit SL ME sequences attached to their 5' ends (Aeby et al. 2010). Finally, we have identified pre-rRNA molecules that are processed by transsplicing in the 5' external transcribed spacer (5'ETS) region in four trypanosomatid species [T. brucei, Trypanosoma cruzi, Leishmania (Leishmania) (Mayer et al. 2012). These results show that such processing events are not restricted to pre-mRNAs in these organisms.In this study, we showed that pre-rRNA trans-splicing is not restricted to the 5'ETS region. In addition, we demonstrated that t...