Sterol accumulation in developing ovaries of the silkworm Bombyx mori in relation to the diapause hormone

Ovary sterol of the silkworm Bombyx mori during pupal-adult development was investigated using ‘diapause’ and ‘non-diapause’ ovaries. It is composed of cholesterol with high relative concentration of more than 80%, β-sitosterol less than 20% and a trace of campesterol. Cholesterol and β-sitosterol contents per pair of ovaries increased strikingly as ovary development proceeded. In sterol concentration per wet weight of ovaries, free forms of cholesterol and β-sitosterol did not increase, or rather inclined to decrease in the former and were almost constant in the latter. However, the ester forms, especially cholesterol ester, increased remarkably during oöcyte maturation. This suggests that this ester may preferably be deposited in oöcyte yolk.Furthermore, the accumulation of sterol esters especially cholesterol ester was higher in ‘diapause’ than ‘non-diapause’ ovaries. It is highly probable that the diapause hormone stimulates the accumulation of cholesterol ester in oöcytes undergoing oögenesis.