Keywords: 
• microplastic /
• fish /
• tissue repair and regeneration /
• gene transcription

Abstract: Microplastic pollution has been considered as a global problem. It has been confirmed that the microplastics in the aquatic environment can be ingested by aquatic organisms, and consequently result in toxicological effects at the various level of biological organization. On the other hand, the ability to restore tissue morphology and function of wildlife is critical for individuals and population. However, our previous study has demonstrated that microplastics can inhibit the fin regeneration in zebrafish larvae, but whether the responses will differ or not when following exposure at different stages of regeneration remains unclear. In this study, the polystyrene microspheres were adopted as model particles of microplastics, and the zebrafish larvae following caudal fin amputation were exposed to microplastics (3 mg·L^-1) at different stages of regeneration (i.e., the pre amputation stage, the early or the late stage of regeneration post amputation). Firstly, the area of regenerating fin and the locomotor behaviors of fish were measured, and the effects of microplastic exposure at different stages were compared morphologically or functionally. Moreover, the transcript level of genes involved in the signaling networks regulating fin regeneration and the immune response were determined to reveal the underlying mechanisms. It was confirmed that microplastic exposure could inhibit the fin regeneration, and the effect was more significant when following exposure at the early stage of regeneration. Similar pattern was observed when the locomotor behaviors of fish exposed at different stages of regeneration were compared. It was seemed that exposure to microplastics down-regulated the transcription of genes related to immune system, and the effects were more significant for the exposure post amputation. Regarding the genes involved in the signaling networks regulating fin regeneration, although the changing trend of transcriptional response differed among genes, the impacts of exposure post amputation were seemed to be more substantial. In conclusion, this study demonstrated the regenerating stages post amputation were the important window of microplastic exposure, and the interaction between the particles and the tissue around the amputated plane was critical for the inhibitive effects of microplastics on fin regeneration.