Related Experiment Video
Updated: Oct 25, 2025
Studying Neurobehavioral Effects of Environmental Pollutants on Zebrafish Larvae
Published on: February 5, 2020
The brominated flame retardant, TBCO, impairs oocyte maturation in zebrafish (Danio rerio)
Darren Van Essen1, Alper James G Alcaraz2, Justin G P Miller1
1Department of Biological Sciences, University of Lethbridge, Lethbridge, Alberta, T1K 3M4, Canada.
Abstract:
The brominated flame retardant, 1,2,5,6-tetrabromocyclooctane (TBCO), has been shown to decrease fecundity in Japanese medaka (Oryzias latipes) and there is indirect evidence from analysis of the transcriptome and proteome that this effect might be due to impaired oogenesis. An assay for disruption of oocyte maturation by chemical stressors has not been developed in Japanese medaka. Thus, using zebrafish (Danio rerio) as a model, objectives of the present study were to determine whether exposure to TBCO has effects on maturation of oocytes and to investigate potential mechanisms. Sexually mature female zebrafish were given a diet of 35.3 or 628.8 μg TBCO / g food for 14 days after which, stage IV oocytes were isolated to assess maturation in response to maturation inducing hormone. To explore potential molecular mechanisms, abundances of mRNAs of a suite of genes that regulate oocyte maturation were quantified by use of quantitative real-time PCR, and abundances of microRNAs were determined by use of miRNAseq. Ex vivo maturation of oocytes from fish exposed to TBCO was significantly less than maturation of oocytes from control fish. The percentage of oocytes which matured from control fish and those exposed to low and high TBCO were 89, 71, and 67%, respectively. Among the suite of genes known to regulate oocyte maturation, mRNA abundance of insulin like growth factor-3 was decreased by 1.64- and 3.44-fold in stage IV oocytes from females given the low and high concentrations of TBCO, respectively, compared to the control group. Abundances of microRNAs regulating the expression of proteins that regulate oocyte maturation, including processes related to insulin-like growth factor, were significantly different in stage IV oocytes from fish exposed to TBCO. Overall, results of this study indicated that impaired oocyte maturation might be a mechanism of reduced reproductive performance in TBCO-exposed fish. Results also suggested that effects of TBCO on oocyte maturation might be due to molecular perturbations on insulin-like growth factor signaling and expression of microRNAs.
Insights
The brominated flame retardant 1,2,5,6-tetrabromocyclooctane (TBCO) impairs zebrafish oocyte maturation. This chemical exposure disrupts insulin-like growth factor signaling and microRNA expression, potentially reducing fish reproductive success.
Area of Science:
- Environmental Toxicology
- Reproductive Biology
- Molecular Endocrinology
Background:
- Brominated flame retardants, like 1,2,5,6-tetrabromocyclooctane (TBCO), are environmental contaminants.
- Previous studies suggest TBCO reduces fecundity in Japanese medaka, possibly via impaired oogenesis.
- A specific assay for TBCO-induced oocyte maturation disruption is lacking in medaka.
Purpose of the Study:
- To determine if TBCO exposure affects oocyte maturation in zebrafish (Danio rerio).
- To investigate the molecular mechanisms underlying TBCO's potential effects on oocyte maturation.
- To establish a model for assessing chemical disruption of oocyte maturation.
Main Methods:
- Zebrafish were fed diets containing low (35.3 μg/g) or high (628.8 μg/g) concentrations of TBCO for 14 days.
- Stage IV oocytes were isolated for ex vivo maturation assessment in response to hormonal induction.
- mRNA and microRNA (miRNA) expression levels were quantified using qRT-PCR and small RNA sequencing (miRNAseq).
Main Results:
- Ex vivo oocyte maturation was significantly reduced in TBCO-exposed zebrafish compared to controls (89% vs. 71% and 67%).
- mRNA abundance of insulin-like growth factor 3 (IGF-3) was significantly decreased in oocytes from TBCO-exposed fish.
- Differential expression of specific microRNAs regulating IGF signaling pathways was observed in TBCO-exposed oocytes.
Conclusions:
- Impaired oocyte maturation is a likely mechanism for reduced reproductive performance in TBCO-exposed fish.
- TBCO's effects on oocyte maturation may involve molecular disruptions in insulin-like growth factor signaling.
- Alterations in microRNA expression patterns contribute to the observed reproductive toxicity of TBCO.
