Accumulation of Yolk Proteins in Insect Oocytes

Abstract

In insects, accumulation of yolk, or vitellogenesis, is a heterosynthetic pro­ cess, in which an extraovarian tissue, the fat body, produces yolk protein precursors ( 1 , 92). Heterosynthetic vitellogenesis occurs even in the most primitive insects, the Apterygota (9, 10, 1 13). Only for two apterygote insects have ultrastructural observations indicated participation of autosynthesis in vitellogensis (9, 10) . This claim, however, requires confirmation by biochem­ ical or immunochemical means . Because of the heterosynthetic nature of vitellogenesis in insects, their oocytes are highly specialized for the specific accumulation of extraovarian yolk protein precursors . Telfer first implicated the role of endocytosis in yolk deposition in insect oocytes . He found selective concentration of some hemolymph-borne proteins in yolk bodies of Hyalophora cecropia oocytes ( 1 29, 1 3 1 ) . Coated vesicles, the cellular structures associated with selective endocytosis, were first observed in oocytes of the mosquito Aedes aegypti ( 1 1 2) . These pioneering studies were followed by numerous electron micro­ scopical and tracer investigations that supported earlier data on the in­ ternalization pathway of extraovarian proteins in follicles and on the role of coated vesicles in yolk deposition in insect oocytes (reviewed in 1 33) .