In alternative splicing RT-PCR assays, we are monitoring the expression shift between different isoforms of an alternative splicing event. Percent Spliced-In (PSI) is a metric based on the long and short isoforms, respectively representing the alternative portion inclusion and exclusion. PSI is calulated as L/(L+S) where L and S are the measured expression of the long and short isoforms, respectively. Thus PSI is interpreted as the expression portion taken by the event inclusion part. PSI are reported as a ratio value between 0 and 1, or as a percentage.

PSI is defined using two isoforms. When there is more than two amplicons detected, the PSI algorithm automatically associates long and short isoforms to the two most abundantly expressed amplicons in all assays for this event (primer pair).

In the heatmap figure below, PSI values are mapped to a rainbow color scale (see figure legend). A grayscale color is used when no PSI value could be obtained for a particular assay:

• no matching detected peak: no peak (amplicon) was detected that could match any isoform of the event.
• filtered out: a PSI value have been calculated, but rejected because of low expression of the isoforms.
• undefined short/long: there is only one amplicon detected and it cannot be unambiguously associated to the short or long isoform.
• no assay: no assay at this primer pair / sample combinaison

Heatmap row labels are clickable and link to the primer pair page.

There is also a PSI data table available to download.