Stress, Locomotion, and Zebrafish Mutant Analysis

Student: Emma Hall ’21
Research Mentor: Karl Clark (Mayo Clinic Department of Biochemistry and Molecular Biology)

The stress response (SR), mediated through the hypothalamic-pituitary-adrenal (HPA) axis, is an organism’s reaction to threats to homeostasis. Proper SR is essential for survival and fitness, but exaggerated or chronic activation of SR leads to stress-aggravated disorders including depression and post-traumatic stress disorder. However, there is minimal understanding on the role of rapid SR in stress-associated disorders.  Within a few minutes of HPA axis activation, a hormonal cascade results in the secretion of glucocorticoids from the adrenal gland in humans and from the interrenal cells (HPI axis) in zebrafish which dictates the behavioral and physiological responses of an organism. Because of the quick timeline, SR excludes transcription-dependent response that require gene expression changes. fkbp5, a co-chaperone protein that binds to glucocorticoid receptor (GR), has been implicated in decreased glucocorticoid receptor activity. Replacing fkbp5 with fkbp4 renders GR more free, increases GR binding affinity to cortisol, and allows GR to translocate into the nucleus more efficiently. We hypothesized that abrogating fkbp5 function will increase locomotor response to acute stressors. To test this hypothesis, we used zebrafish with a frameshift allele (116 bp deletion) in exon 2 of fkbp5 and subjected larval zebrafish (5 days-post-fertilization) to abrupt light changes. fkbp5 heterozygous and homozygous fish showed significantly increased locomotion after 1-min white light illumination [baseline (15-min infrared (dark)) – white light (1 min) – post-treatment (30-min infrared)] and in a repeated 7.5-min dark-light cycling assay. Our findings indicate a role for fkbp5 in rapid SR. Current work is focused on generating “knock-in” mutant strains to compare the phenotypes with frameshift mutants. Our behavioral assay-based approach may discover novel genetic modifiers of rapid stress response.

When faced with a threat, animals respond in a distinct way called the stress response (SR). Concurrently with the fight-or-flight response of the nervous system, SR takes effect within minutes maintaining the body’s energy levels (e.g. blood sugar) while causing rapid behavioral changes. However, there is little known about the genes responsible for this rapid SR. Using zebrafish and focusing on one gene (fkbp5) known to play a role in long-term SR, we found that fkbp5 also participates in rapid behavioral SR. We aim to discover new genes for rapid SR and increase our understanding on the relationship between rapid and chronic SR.