Developmental toxicity of the environmental pollutant 4-nonylphenol in zebrafish

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4-Nonylphenol (4-NP), an estrogen mimicking compound is produced by biodegradation of alkylethoxylates. It is well established that 4-NP can affect the development of aquatic animals by disrupting the endocrine signals. Here we show for the first time in zebrafish that 4-NP does not only target the neuroendocrine system but also the notochord and the muscle. The notochord malformation was first evident as distortions at 24 hours post fertilization (hpf) which within 24 h appeared as kinks and herniations. The notochord phenotype was accompanied by reduced motility and impaired swimming behavior. Whole-mount in situ hybridization using chordamesoderm markers and electron microscopic analysis showed failure in the notochord differentiation and disruption of the perinotochordal basement membrane. Late larval stages of 4-NP treated embryos displayed abnormal mineralization, vertebral curvature, fusion of vertebral bodies and abnormal extension of haemal arches. The muscle structure and the maximal active force in isolated muscle preparations were similar between 4-NP exposed and of control embryos, suggesting that 4-NP did not induce major changes in striated muscle function. However, repeated electrical stimulation (> 40 Hz) of the 4-NP exposed larvae revealed an impaired relaxation between stimuli, possibly reflecting an alteration in the relaxant mechanisms (e.g. in cellular Ca 2+ removal) which could explain the abnormal swimming pattern exhibited by 4-NP exposed larvae. Additionally, we demonstrate that the expression levels of the stress hormone, corticotropin releasing hormonewere elevated in the brain following 4-NP treatment. We also observed a significant decrease in the transcript levels of luteinizing hormone b at early larval stages. Collectively, our results show that 4-NP is able to disrupt the notochord morphogenesis, muscle function and the neuroendocrine system. These data suggest that 4-NP enduringly affects the embryonic development in zebrafish and that this compound might exert these deleterious effects through diverse signaling pathways.