Most "dark matter" transcripts are associated with known genes.

Area of Science:

• Genomics
• Molecular Biology
• Transcriptomics

Background:

• Previous studies suggested extensive transcription beyond annotated genes.
• The quantity and nature of these novel transcripts remained largely unknown.

Purpose of the Study:

• To quantify and characterize transcripts in PolyA+ RNA from human and mouse tissues.
• To compare RNA-Seq and tiling array data for transcript identification.

Main Methods:

• Utilized single- and paired-end RNA-Sequencing (RNA-Seq) data.
• Employed tiling arrays for transcript analysis.
• Focused on PolyA+ RNA from human and mouse tissues.

Main Results:

• RNA-Seq identified significantly fewer transcribed regions outside known exons and non-coding RNAs compared to tiling arrays.
• Most novel transcripts were intronic or intergenic, often near known genes, suggesting roles in alternative polyadenylation or novel exons.
• Identified 4,544 new exons affecting 3,554 genes.
• Discovered several thousand small, conserved transcripts originating from open chromatin regions.

Conclusions:

• While bona fide novel intergenic transcripts exist, their number and abundance are generally low.
• The mammalian genome is not as pervasively transcribed as previously suggested.
• RNA-Seq provides a more refined view of transcription compared to tiling arrays.