What is Gene set enrichment?

Enrichment analysis is a technique commonly used to interpret add biological context to a list of genes (, such as list of significant genes). The procedure is based on assigning genes to groups , based on their characteristics and then finding overrepresented groups in filtered gene lists .

Upon selecting a Feature list data node, the Biological interpretation section will become visible in the context sensitive menu. To perform the analysis, select the Enrichment analysis option (Figure 1).

Then select the gene set you want to use (Figure 2). The files available for the current Genome build are using a Fisher's exact test.

Running Gene set enrichment

We recommend filtering to a set of genes you want to test for enrichment, but Gene set enrichment will run on any Feature list data node. 

• Click a Feature list data node
• Click the Biological interpretation section of the toolbox
• Click Gene set enrichment 
• Configure the background gene list (optional)

The background gene list is used as the list of possible genes. By default, this is the genes included in the selected gene set database. If your assay limits the genes that could be detected, you may want to specify a background list.

• Choose the Gene set 

The gene sets available for the current Assembly are listed under the Gene set drop-down list. Click the Finish button to start the analysis.  The assembly is automatically selected, if possible. If the assembly cannot be detected, you can specify it using a drop-down menu.

• Click Finish to run (Figure 1)

By default, the groups are defined by Gene Ontology (GO), a bioinformatics initiative to unify the representation of gene and gene product attributes across various species [1, 2]. There are three main GO groups which are further divided into subgroups:

• biological process
• molecular function
• cellular component

Alternatively, selecting the Add gene ontology source from the Gene set drop down list option opens another dialog (Figure 3), where you can either Download gene set from Partek^® (Recent GO database gene sets for human, mouse and rat are supportedavailable) or Import gene set. The latter option takes you to the file browser, where you can point to the file that you want to use (not shown). Partek^® Flow^® accepts .gmt files as gene set inputs.

The result is stored under an Enrichment task node. To open it, double click on the node or select the respective Task report from the context sensitive menu.

Gene set enrichment task report

Figure 4 shows an example GO enrichment example Gene set enrichment task report. The table contains one GO category gene set per row (Gene set column; the column entries are hyperlinks when using the distributed GO gene sets), with the category name in the Description column. The categories are ranked by the Enrichment score, which is the negative natural logarithm of the enrichment p-value (P-value column) derived from Fisher's exact test on the underlying contingency table. The higher the enrichment score, the more overrepresented the GO category is within the input list of significant genes. The columns can be searched by typing in the search term in the respective box (and hitting Enter), or sorted by selecting the double arrow icon ( ).

The contingency table (Figure 5) can be displayed by selecting the View gene breakdown chart icon on the right (). The term "list" refers to the list of significant genes, while the term "set" refers to the respective GO category. The first row of the contingency table is also seen in the report, namely the Genes in list and Genes not in list columns.

The View extra details () button provides additional information on the GO category (Figure 6). In addition to the details already given in the report, a full list of Genes in list and Genes not in list can be inspected and downloaded (Download data) to the local computer as a text file.

As previously mentioned, if you are using the GO gene sets distributed by Partek, the GO identifiers in the first column are hyperlinks to the Gene Ontology web-site entries (an example shown in Figure 7).

References

1. Ashburner M, Ball CA, Blake JA et al. Gene Ontology: tool for the unification of biology. Nat Genetics. 2000; 25:25-29.
2. The Gene Ontology Consortium. Gene Ontology Consortium: going forward. Nucleic Acids Res. 2015; 43:D1049-1056.Recommended citations from the Geneontology.org website

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