Meeting Abstract
Downstream molecular consequences of stress responses are not well known in free-ranging marine mammals, hindering understanding of stress-related pathologies and regulation of metabolic activity by stress hormones. We examined cellular responses to a stress challenge in juvenile northern elephant seals by stimulating the hypothalamic-pituitary-adrenal (HPA) axis with exogenous adrenocorticotropic hormone (ACTH) and profiling resultant changes in tissue gene expression using transcriptomics (RNA sequencing). Global gene expression changes were analyzed in the inner layer of blubber, a metabolically active tissue that responds rapidly to fluctuations in stress hormone levels. We sequenced and assembled the first blubber transcriptome, producing over 350,000 assembled transcripts, including a number of seal-specific adipose genes with no homology to terrestrial mammal proteins. The acute response to ACTH was measured two hours after administration and involved significant elevation in circulating cortisol and aldosterone and alteration in expression levels of over 200 transcripts. Differentially expressed genes included key mediators of lipid metabolism, inflammation, and cell proliferation, global transcriptional regulators, and smooth muscle and endothelial markers of smooth muscle due to the extensive vascularization of marine mammal blubber tissue. This study provides a number of marine mammal-specific blubber and stress markers and complements previous work on the elephant seal muscle transcriptome response to ACTH, furthering understanding of how stress responses are integrated across multiple tissues in marine mammals.
