Comparing Bulk RNA Sequencing and Ultrafast RNA-Seq

Standard bulk RNA-seq, provides unparalleled coverage and sensitivity, making it the gold standard for comprehensive transcriptome analysis. It involves sequencing of extracted mRNA or total RNA, either by polyA selection or rRNA depletion, respectively. Bulk RNA-seq can be applied to prokaryotes, eukaryotes and RNA viruses. Because the entire RNA transcript is sequenced, bulk RNA-seq can detect alternative splicing events, fusion genes, and novel isoforms. It offers flexibility in depth of sequencing; however, it tends to be deeper sequencing (typically 30 M+ paired end reads for most animals) to detect both abundant and rare transcripts. As a result, bulk RNA-seq is suitable for research into complex biological systems, novel insights, rare disease mechanisms, and biomarker discovery, while also being suitable for de novo transcriptome assembly in plants, animals, and bacteria.

3’ end counting RNA-seq is well-suited for studies where the detection of highly expressed genes is the main goal, enabling high-level screening for major changes in expression including compound screening. This method provides limited insight beyond gene counts (no exon-level resolution). It is often coupled with cost reduction actions upstream, like direct from cell lysate library preparation, versus sequencing from extracted RNA, further constraining input sample types to animal cell pellets. By sequencing only the 3’ end of the polyadenylated transcript, fewer reads are needed per sample to capture gene-level detection; however, low-expressing genes may not be detected. Finally, 3’ end counting requires a reference transcriptome for analysis.

Bulk RNA-Seq vs. 3’ End Counting: Factors to Consider

Choosing between bulk and 3’ end counting RNA-seq should be guided by experimental objectives, sample type, and required analytical resolution. Bulk RNA-seq is recommended when comprehensive transcriptome coverage, discovery of novel features, or detection of rare transcripts are essential, as well as for any bacterial or plant-based RNA analysis. Conversely, 3’ end counting is ideal for large-scale screening of extracted RNA or animal cell pellets where cost is prioritized, at the sacrifice of transcript-level information. In the US, GENEWIZ also now offers bulk rna-seq as fast as five business days with our new Lightning RNA-Seq service.