3.4 Functional enrichment
Gene ontology (GO) analysis for biological processes shows very similar
enrichment of GO terms within tissue types regardless of sampling
method. Among tissue types, certain GO terms are common such as RNA
processing and RNA modification, which is similar to a previous fish
gene expression study (Passow et al. 2018). There is also variation in
the number and diversity of enriched GO terms depending on the tissue
type (Supporting Information Figure S4). There are many more enriched GO
terms associated with genes that are highly expressed in muscles (6 to
14 categories) compared to gills (0 to 5 categories), while the number
of enriched GO categories associated with comparisons of gills (14 to 15
categories) versus blood (7 to 11 categories), and blood (9 to 11
categories) versus muscle (6 to 10 categories), are similar. Gills in
particular are enriched for many GO categories related to major cell
cycle processes, which fits with their active growth and turnover as
epithelial cells at the aquatic interface (Stolper et al. 2019).
Regardless of the sampling method, genes associated with cellular stress
appear to be more highly expressed in blood and gills compared to
muscle, potentially indicating tissue-specific physiological effects of
the sampling process.