Growing Oocytes Need Zinc: Zinc Deficiency in the Preantral Ovarian Follicle

Objective To evaluate the effect of zinc deficiency on oocyte development in the preantral ovarian follicle – a novel developmental stage for micronutrient investigation. Methods Oocyte-granulosa cell complexes were collected from preantral ovarian follicles of 14 day old CD-1 mice and cultured on collagen membranes under control, zinc-deficient, or rescue conditions. Oocyte diameter was measured from brightfield images taken with an Olympus DP20 microscope digital camera. Chromatin arrangement and nucleolar development was observed after DAPI staining. Gene expression was measured with qPCR. Meiotic competence was measured by exposing cultured oocyte-granulosa cell complexes to Epidermal Growth Factor (EGF) to mimic the in-vivo ovulatory signal (maturation media). The ability of the oocytes to undergo meiotic division was assessed 24 hours after EGF treatment. Results Zinc deficiency disrupted oocyte growth in vitro. Zinc deficient oocytes were smaller than control or rescue on day 4 (p<0.001) and 6 (p<0...