Preoviposition activation of cathepsin-like proteinases in degenerating ovarian follicles of the mosquito Culex pipiens pallens

Within developing ovaries of many insects, some developing follicles or ooc ytes usually degenerate (follicular atresia or oosorption), while the other s may continue to grow to maturity, thus maintaining the balance between th e number of eggs and reproductive circumstances such as available nutrients . To help clarify the phenomenon of follicular atresia during ovarian devel opment, we examined cysteine proteinases stored in mosquito Culex pipiens p ollens ovaries. First, analysis using synthesized substrates showed that ca thepsin B- and L-like proteinases gradually accumulated in the developing o varies after a blood meal, which required more than 10 min of preincubation under acidic conditions to reach their maximum activities. However, homoge nates of degenerating follicles 3 days after feeding showed proteolytic act ivities without acid treatment, suggesting that the proteinases had already been activated, while the extract of normally developing follicles collect ed from the same ovaries required more than 10 min of acid preincubation to reach the optimum activities, suggesting that the enzymes remained as inac tive forms. Chemical and immunohistochemical analyses showed that more prot einases are located in the cytoplasm, rather than being associated with yol k granules. Ovarian proteinases, which are believed to become activated at the onset of embryogenesis, should also be activated during oogenesis, pres umably to enhance oosorption. (C) 2001 Academic Press.