Meeting Abstract
Glucocorticoid hormones mediate stress responses in all vertebrates, from teleost fishes to mammals. In teleosts the primary glucocorticoid, cortisol, is synthesized by the interrenal gland via a series of enzyme-mediated reactions. Cortisol synthesis in adults is controlled by hormones produced via the hypothalamic-pituitary-interrenal (HPI) axis in response to stressors. The hypothalamic peptide corticotropin-releasing hormone (CRH) stimulates release of the pituitary protein adrenocorticotropin hormone (ACTH), which stimulates interrenal cortisol production. Cortisol exerts its effects on target cells via two types of receptors, the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR). The timing and sequence of events that leads to a functioning HPI axis in developing teleosts are not fully known. To address this gap, we measured the mRNA from genes involved in cortisol synthesis and signaling throughout embryogenesis in two model fishes, the zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes). We isolated RNA from embryos collected at multiple developmental stages in both species, and used qPCR to measure relative mRNA levels of key HPI axis genes, including CRH, steroidogenic acute regulatory protein (StAR), and MR. In zebrafish, MR transcript levels remained fairly constant throughout embryo development, whereas in medaka, MR transcripts increased 10-fold. Zebrafish CRH mRNA doubled from 6 hours post fertilization (hpf) to hatching (48 hpf). However, in medaka, CRH mRNA levels rose over 90-fold from 2 days post fertilization (dpf) to hatch at 8 dpf. In zebrafish, StAR mRNA levels increased 40-fold from 24 hpf to hatch, whereas levels rose only 5-fold in medaka. In conclusion, we found noteworthy differences in mRNA profiles for CRH, MR, and StAR in both species.
