Molecular programming of the corticosteroid stress axis during zebrafish development

Area of Science:

• Endocrinology
• Developmental Biology
• Neuroscience

Background:

• The hypothalamus-pituitary-interrenal (HPI) axis regulates stress response in teleosts.
• Limited knowledge exists on the molecular mechanisms of HPI axis development and stress response onset in early life stages.

Purpose of the Study:

• To investigate the molecular events and gene expression patterns of the HPI axis during zebrafish development.
• To understand the timing of cortisol synthesis and stressor-induced response in developing zebrafish.

Main Methods:

• Analysis of mRNA expression for key HPI axis genes (CRF, POMC, MC2R, StAR, P450scc) in zebrafish embryos and larvae.
• Monitoring of cortisol levels and stressor-induced responses at different developmental stages.

Main Results:

• Key HPI axis gene transcripts (CRF, POMC, MC2R, StAR, P450scc) are detected during embryogenesis prior to hatching.
• mRNA levels of MC2R, StAR, and P450scc increase before the rise in basal larval cortisol post-hatch.
• A stressor-induced cortisol response is observed at 97 hours post-fertilization (hpf), despite cortisol synthesis at hatch.

Conclusions:

• Zebrafish exhibit early expression of HPI axis components but a delayed onset of the stressor-induced cortisol response.
• The delayed stress response is hypothesized to result from the late development of neural pathways relaying stress stimuli.
• Zebrafish serve as a valuable model for studying the development of the vertebrate corticoid stress axis.