Meeting Abstract
The zebrafish (Danio rerio) is a commonly studied model organism utilized for stress research due to functional similarities between the hypothalamus–pituitary–adrenal (HPA) axis and teleost hypothalamus–pituitary–interrenal (HPI) axis. The Japanese medaka (Oryzias latipes) is another promising model teleost for stress axis research; however, there has been considerably less research done on the embryonic development of key stress axis components in this species compared to zebrafish. To further the utility of both species as model organisms for stress research, we have characterized the development of the HPI axis in both by measuring expression levels of genes encoding key HPI hormones, receptors, and enzymes during embryonic development. Toward this goal, we isolated total RNA from zebrafish embryos collected at 12 time points, from 10 hours post-fertilization (hpf) to just prior to hatching at 48 hpf, and from medaka embryos collected at 9 time points, from 2 days post fertilization (2 dpf) to just prior to hatching at 8 dpf. We used quantitative PCR to determine the relative expression of the target HPI axis genes normalized to the housekeeping gene β-actin. We found that in the medaka, glucocorticoid receptor (GR) mRNA levels significantly increase from 2 days post fertilization (dpf) through 6dpf, then remain fairly steady until 8 dpf. Conversely, in the zebrafish, we found that GR mRNA levels remain relatively unchanged from 10 hours post fertilization (hpf) up to 48 hpf. These initial results indicate that there are critical differences in the early development of the HPI axis among teleost fishes.
