Abstract：Microcystin-LR (MC-LR) is a widespread toxin produced by Cyanobacteria that pollutes the water environment. Animal studies provide strong evidence of positive associations between microcystins (MCs) exposure and reproductive toxicity, representing a threat to human reproductive health and the biodiversity of wild life. However, little is known about its toxic effects on animal oocytes. This study evaluated the toxic effects of MC-LR on porcine (Sus scrofa) oocyte in vitro maturation. The cumulus-oocyte complexes (COCs) were exposed to 0, 20, 40, 60 μg/mL MC-LR for maturation culture. Immunofluorescent staining coupled with confocal microscopy imaging techniques was used to examine the chromosomes alignment and spindle tubulin distribution of the MC-LR treated oocytes. The results showed that the maturation rate of pig oocytes exposed to MC-LR decreased in a dose-dependent manner. After 44 h in culture, most of the control oocytes had extruded the first polar body and arrested at the MⅡ stage in vitro, and the first polar body extrusion rate was 72.81%. However, the rate was significantly reduced to 56.71% (P<0.05) and 45.00% (P<0.01) when treated with 40 and 60 μg/mL of MC-LR, respectively. After MC-LR (60 μg/mL) treatment, the proportion of the oocytes arrested in telophase Ⅰ (TⅠ) stage was significantly increased from 10.63% to 45.49% (P<0.001), and the proportion of the oocytes showed obvious defects in homologous chromosome segregation and alignmen was also increased from 11.94% to 44.33% (P<0.001). Further subcellular structure examination results showed that the proportion of oocytes with spindle structure disorder increased significantly after MC-LR treatment. The results of this study indicated that MC-LR had obvious toxic damage to the spindle structure of porcine oocyte, resulting in abnormal alignment of homologous chromosomes and arrestment of meiosis in TⅠ stage, eventually resulted in failure of porcine oocyte maturation (P<0.01). The results will provide an experimental basis for further understanding the reproductive toxicity and its mechanism of MC-LR, and also provide experimental reference for effective prevention and treatment of diseases related to the reproductive toxicity of MC-LR
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