Fig. 4

Effects of PM_2.5 exposure on activation of primordial ovarian follicles. Female mice were exposed to concentrated ambient PM_2.5 or filtered air as described for Fig. 1 and ovaries were processed for immunostaining for the proliferation protein Ki67 as detailed in Methods. Representative photomicrographs taken with 40 × objective show Ki67-positive follicles with brown stained granulosa cell nuclei in air control and PM_2.5 ovaries. Red arrows point to primary follicles with Ki67-positive granulosa cells. Black arrowhead points to primordial follicle with Ki67-negative granulosa cells. Scale bars, 50 μm. The graph shows the means ± SEM percentages of Ki67-positive primordial and primary follicles. PM_2.5 exposure significantly increased the percentage of primary follicles with Ki67-positive granulosa cells. *P < 0.05 compared to air controls. N = 6/group