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Background The developing mouse kidney is currently the best-characterized model of organogenesis at a transcriptional level. Detailed spatial maps have been generated for gene expression profiling combined with systematic in situ screening. These studies, however, fall short of capturing the transcriptional complexity arising from each locus due to the limited scope of microarray-based technology, which is largely based on "gene-centric" models. Results To address this, the polyadenylated RNA and microRNA transcriptomes of the 15.5 dpc mouse kidney were profiled using strand-specific RNA-sequencing (RNA-Seq) to a depth sufficient to complement spatial maps from pre-existing microarray datasets. The transcriptional complexity of RNAs arising from mouse RefSeq loci was catalogued; including 3568 alternatively spliced transcripts and 532 uncharacterized alternate 3' UTRs. Antisense expressions for 60% of RefSeq genes was also detected including uncharacterized non-coding transcripts overlapping kidney progenitor markers, Six2 and Sall1, and were validated by section in situ hybridization. Analysis of genes known to be involved in kidney development, particularly during mesenchymal-to-epithelial transition, showed an enrichment of non-coding antisense transcripts extended along protein-coding RNAs. Conclusion The resulting resource further refines the transcriptomic cartography of kidney organogenesis by integrating deep RNA sequencing data with locus-based information from previously published expression atlases. The added resolution of RNA-Seq has provided the basis for a transition from classical gene-centric models of kidney development towards more accurate and detailed "transcript-centric" representations, which highlights the extent of transcriptional complexity of genes that direct complex development events.

The functionality of sense–antisense transcripts (SATs), although widespread throughout the mammalian genome, is largely unknown. Here, we analyzed the SATs expression and its associated promoter DNA methylation status by surveying 12 tissues of mice to gain insights into the relationship between expression and DNA methylation of SATs. We have found that sense and antisense expression positively correlate in most tissues. However, in some SATs with tissue-specific expression, the expression level of a transcript from a CpG island-bearing promoter is low when the promoter DNA methylation is present. In these circumstances, the expression level of its opposite-strand transcript, especially when it is poly(A)-negative was coincidentally higher. These observations suggest that, albeit the general tendency of sense–antisense simultaneous expression, some antisense transcripts have coordinated expression with its counterpart sense gene promoter methylation. This cross-strand relationship is not a privilege of imprinted genes but seems to occur widely in SATs.