The effects of progesterone on transcriptional expression profiles of genes associated with hypothalamic–pituitary–gonadal and hypothalamic–pituitary–adrenal axes during the early development of zebrafish (Danio rerio)

• Zebrafish embryos were exposed to progesterone for 144 hpf.
• The transcriptional effects of progesterone on the HPG and HPA axes were evaluated.
• Progesterone could alter mRNA expression of target genes along HPG and HPA axes.
• The molecular effects of progesterone are time- and concentration-dependent manners.

Progesterone (P4) has been reported in surface water, and it may have adverse effects on aquatic organisms. This study provided the transcriptional effects of P4 during the early development of zebrafish. Zebrafish embryos were exposed for 144 h post fertilization (hpf) to 0, 6, 45 and 90 ng L−1 P4, and transcriptional expression profiles of the hypothalamic–pituitary–gonadal (HPG) and hypothalamic–pituitary–adrenal (HPA) axes were assessed every day. For the receptor signaling pathways, P4 significantly induced the transcript of Pgr gene above 45 ng L−1 at 72 and 144 hpf, but inhibited its transcript above 6 ng L−1 at 96 and 120 hpf. A significant up-regulation of Vtg1 mRNA was observed at 6 ng L−1 P4 or higher at 24, 96 and 144 hpf. For the steroidogenic pathways, the transcriptional expression of Cyp11a1 and Hsd17b3 mRNAs was mediated by 6 ng L−1 P4 or higher according to different exposure time points. In addition, P4 resulted in a significant induction of Cyp19a1a and Cyp11b mRNA expression while it caused a significant inhibition of Hsd11b2 mRNA expression above 6 ng L−1. For the other target genes related to hypothalamic and pituitary hormones, P4 mainly modulated the transcripts of Gnrh2, Fshb and Lhb genes at 6 ng L−1 or higher. The overall results from the present study indicate that P4 at environmentally relevant concentrations could cause the potential effects on zebrafish reproductive and adrenal endocrine systems by interfering with the HPG and HPA axes.