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Open Access Highly Accessed Research article

Cross-species mapping of bidirectional promoters enables prediction of unannotated 5' UTRs and identification of species-specific transcripts

Helen Piontkivska2, Mary Q Yang1, Denis M Larkin3, Harris A Lewin34, James Reecy5 and Laura Elnitski1*

Author affiliations

1 National Human Genome Research Institute, National Institutes of Health, Rockville, MD, 20852, USA

2 Department of Biological Sciences, Kent State University, Kent, Ohio 44242, USA

3 Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61821 USA

4 Institute for Genome Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61821, USA

5 Department of Animal Science, Iowa State University, Ames, IA 50011, USA

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Citation and License

BMC Genomics 2009, 10:189  doi:10.1186/1471-2164-10-189

Published: 24 April 2009

Abstract

Background

Bidirectional promoters are shared regulatory regions that influence the expression of two oppositely oriented genes. This type of regulatory architecture is found more frequently than expected by chance in the human genome, yet many specifics underlying the regulatory design are unknown. Given that the function of most orthologous genes is similar across species, we hypothesized that the architecture and regulation of bidirectional promoters might also be similar across species, representing a core regulatory structure and enabling annotation of these regions in additional mammalian genomes.

Results

By mapping the intergenic distances of genes in human, chimpanzee, bovine, murine, and rat, we show an enrichment for pairs of genes equal to or less than 1,000 bp between their adjacent 5' ends ("head-to-head") compared to pairs of genes that fall in the same orientation ("head-to-tail") or whose 3' ends are side-by-side ("tail-to-tail"). A representative set of 1,369 human bidirectional promoters was mapped to orthologous sequences in other mammals. We confirmed predictions for 5' UTRs in nine of ten manual picks in bovine based on comparison to the orthologous human promoter set and in six of seven predictions in human based on comparison to the bovine dataset. The two predictions that did not have orthology as bidirectional promoters in the other species resulted from unique events that initiated transcription in the opposite direction in only those species. We found evidence supporting the independent emergence of bidirectional promoters from the family of five RecQ helicase genes, which gained their bidirectional promoters and partner genes independently rather than through a duplication process. Furthermore, by expanding our comparisons from pairwise to multispecies analyses we developed a map representing a core set of bidirectional promoters in mammals.

Conclusion

We show that the orthologous positions of bidirectional promoters provide a reliable guide to directly annotate over one thousand regulatory regions in sequences of mammalian genomes, while also serving as a useful tool to predict 5' UTR positions and identify genes that are novel to a single species.