Biomedical subjects

Fabrice Lopez

Publications and source records attributed to Fabrice Lopez.

4 recordsLinked to original sources

PubMed2006

The disparate nature of "intergenic" polyadenylation sites.

The termination of mature eukaryotic mRNAs occurs at specific polyadenylation sites located downstream from stop codons in the 3'-untranslated region (UTR). An accurate delineation of these sites is essential for the study of 3'-UTR-based gene regulation and for the design of pertinent probes for transcriptome analysis. Although typical poly(A) sites are located between 0 and 2 kb from the stop codon, EST sequence analyses have identified sites located at unexpectedly long ranges (5-10 kb) in a number of genes. Here we perform a complete mapping of EST and full-length cDNA sequences on the mouse and human genome to observe putative poly(A) sites extending beyond annotated 3'-ends and into the intergenic regions. We introduce several quality parameters for poly(A) site prediction and train a classification tree to associate P-values to predicted sites. We observe a higher than background level of high-scoring sites up to 12-15 kb past the stop codon, both in human and mouse. This leads to an estimate of about 5000 human genes having unreported 3'-end extensions and about 3500 novel polyadenylated transcripts lying in present "intergenic" regions. These high-scoring, long-range poly(A) sites corresponding to novel transcripts and gene extensions should be incorporated into current human and mouse gene repositories.

3' Untranslated Regions↗

PubMed2006

Conservation of alternative polyadenylation patterns in mammalian genes.

BACKGROUND: Alternative polyadenylation is a widespread mechanism contributing to transcript diversity in eukaryotes. Over half of mammalian genes are alternatively polyadenylated. Our understanding of poly(A) site evolution is limited by the lack of a reliable identification of conserved, equivalent poly(A) sites among species. We introduce here a working definition of conserved poly(A) sites as sites that are both (i) properly aligned in human and mouse orthologous 3' untranslated regions (UTRs) and (ii) supported by EST or cDNA data in both species. RESULTS: We identified about 4800 such conserved poly(A) sites covering one third of the orthologous gene set studied. Characteristics of conserved poly(A) sites such as processing efficiency and tissue-specificity were analyzed. Conserved sites show a higher processing efficiency but no difference in tissular distribution when compared to non-conserved sites. In general, alternative poly(A) sites are species-specific and involve minor, non-conserved sites that are unlikely to play essential roles. However, there are about 500 genes with conserved tandem poly(A) sites. A significant fraction of these conserved tandems display a conserved arrangement of major/minor sites in their 3' UTR, suggesting that these alternative 3' ends may be under selection. CONCLUSION: This analysis allows us to identify potential functional alternative poly(A) sites and provides clues on the selective mechanisms at play in the appearance of multiple poly(A) sites and their maintenance in the 3' UTRs of genes.

3' Untranslated Regions↗

PubMed2006

Differential repression of alternative transcripts: a screen for miRNA targets.

Alternative polyadenylation sites produce transcript isoforms with 3' untranslated regions (UTRs) of different lengths. If a microRNA (miRNA) target is present in the UTR, then only those target-containing isoforms should be sensitive to control by a cognate miRNA. We carried out a systematic examination of 3' UTRs containing multiple poly(A) sites and putative miRNA targets. Based on expressed sequence tag (EST) counts and EST library information, we observed that levels of isoforms containing targets for miR-1 or miR-124, two miRNAs causing downregulation of transcript levels, were reduced in tissues expressing the corresponding miRNA. This analysis was repeated for all conserved 7-mers in 3' UTRs, resulting in a selection of 312 motifs. We show that this set is significantly enriched in known miRNA targets and mRNA-destabilizing elements, which validates our initial hypothesis. We scanned the human genome for possible cognate miRNAs and identified phylogenetically conserved precursors matching our motifs. This analysis can help identify target-miRNA couples that went undetected in previous screens, but it may also reveal targets for other types of regulatory factors.

Animals↗

PubMed2006

AltTrans: transcript pattern variants annotated for both alternative splicing and alternative polyadenylation.

BACKGROUND: The three major mechanisms that regulate transcript formation involve the selection of alternative sites for transcription start (TS), splicing, and polyadenylation. Currently there are efforts that collect data & annotation individually for each of these variants. It is important to take an integrated view of these data sets and to derive a data set of alternate transcripts along with consolidated annotation. We have been developing in the past computational pipelines that generate value-added data at genome-scale on individual variant types; these include AltSplice on splicing and AltPAS on polyadenylation. We now extend these pipelines and integrate the resultant data sets to facilitate an integrated view of the contributions from splicing and polyadenylation in the formation of transcript variants. DESCRIPTION: The AltSplice pipeline examines gene-transcript alignments and delineates alternative splice events and splice patterns; this pipeline is extended as AltTrans to delineate isoform transcript patterns for each of which both introns/exons and 'terminating' polyA site are delineated; EST/mRNA sequences that qualify the transcript pattern confirm both the underlying splicing and polyadenylation. The AltPAS pipeline examines gene-transcript alignments and delineates all potential polyA sites irrespective of underlying splicing patterns. Resultant polyA sites from both AltTrans and AltPAS are merged. The generated database reports data on alternative splicing, alternative polyadenylation and the resultant alternate transcript patterns; the basal data is annotated for various biological features. The data (named as integrated AltTrans data) generated for both the organisms of human and mouse is made available through the Alternate Transcript Diversity web site at http://www.ebi.ac.uk/atd/. CONCLUSION: The reported data set presents alternate transcript patterns that are annotated for both alternative splicing and alternative polyadenylation. Results based on current transcriptome data indicate that the contribution of alternative splicing is larger than that of alternative polyadenylation.

Alternative Splicing↗