Elongation of in vitro cultured ovarian follicles in the mosquito, Culex pipiens pallens

Ovarian follicles dissected from female Culex pipiens pallens 3 d after a blood meal were cultured in PBS-based medium and morphological changes were recorded as time-lapse movies. The dissected follicles, already reaching stage III, were ovoid in shape, ca 300 μm long, and 180 μm wide. The oocyte had almost finished yolk protein uptake, and the cytoplasm was filled entirely with yolk granules. From 2 to 4 h after the culture started, the follicles started to elongate dramatically to reach a length of 450–550 μm during the next few hours. After culturing for 24–30 h, the follicles had reached stage V, assuming the shape of normal mature eggs with a micropyle apparatus. Since cytochalasin D or colchicine completely or partially inhibited such follicle elongation and maturation, contraction of cytoskeletons made of actin filaments or microtubules may play a significant role in this phenomenon.