5’ isomiRs analysis
The function of a miRNA is largely defined by its seed sequence, which is a stretch of nucleotides from positions 2 to 7. Recent literature has shown that cleavage by either DROSHA or DICER1 at alternative sites can generate 5’ isomiRs with altered seed sequences (Gu et al., 2012). This process is known as seed shift. The mechanisms regulating seed shift are not yet fully understood, but include aspects such as changes in the secondary structure of miRNA precursors (Gu et al., 2012; Ma et al., 2013; Bofill-De Ros, Kasprzak, et al., 2019) and/or the recruitment of RNA-binding proteins (Kim et al., 2020). The “5’ isomiRs analysis” section facilitates the analysis of this phenomenon in the pan-cancer datasets. Users can find reports of the 5’ Fidelity index and the Effective Number of seeds. The 5’ Fidelity index is an average of the cleavage site position offset weighted by the number of supporting reads, while the Effective Number of seeds is calculated as an inverted Simpson index.
- N: Effective Number of seeds
- p: Ratio of each seed generated by 5' isomiRs of a given miRNA [range 0 to 1]
