Effects of melatonin treatment in vitro on the meiotic progression, spindle/chromosome structure and euploidy of aged oocytes. (A) The kinetics of PBE was recorded in young (n = 68), aged (n = 58), melatonin-treated (n = 64) and melatonin + luzindole-treated (n = 57) oocytes at consecutive time points of post-GVBD. (B) Representative images of spindle morphologies and chromosome alignment in young, aged, melatonin-treated and melatonin + luzindole-treated oocytes. Scale bar, 3 μm. (C) The rate of aberrant spindle with misaligned chromosome was recorded in young (n = 58), aged (n = 46), melatonin-treated (n = 51) and melatonin + luzindole-treated (n = 43) oocytes. (D) Representative images of euploid and aneuploid MII eggs. Chromosome spreading was performed to count the number of chromosomes in young, aged, melatonin-treated and melatonin + luzindole-treated oocytes. Scale bar, 5 μm. (E) The rate of aneuploid eggs was recorded in young (n = 35), aged (n = 34), melatonin-treated (n = 2) and melatonin + luzindole-treated (n = 27) oocytes. Control: young oocytes cultured in M16 medium; Vehicle: aged oocytes cultured in M16 medium containing ethanol and DMSO; Mel: aged oocytes cultured in M16 medium supplemented with melatonin; Luz: aged oocytes cultured in M16 medium supplemented with melatonin and luzindole. Data were presented as mean percentage (mean ± SEM) of at least three independent experiments. *P < 0.05, **P < 0.01, ***P < 0.001.