The ultrastructure of oogenesis in Culex theileri

Abstract

The 12-36 h post blood meal (PBM) oocyte in C. theileri is characterized by a dramatic increase in the quantity of protein with concomitant changes in the adjacent follicular epithelium. The cytoplasm shows a preponderance of mitochondria and rough endoplasmic reticulum in proportion to free ribosomes. Numerous Golgi complexes, which bud off secretory granules, are also found scattered in the cytoplasm. These changes are concerned with the deposition of the vitelline membrane and by 36 h PBM, a continuous vitelline membrane is formed at the follicle cell-oocyte interface. Vitellogenesis appears to be completed by 48 h PBM and the final maturation stages are concerned solely with deposition of the chorionic membrane. In C. theileri the chorionic membrane seems to be synthesized in a similar manner to the vitelline membrane; namely from the aggregation of secretory droplets and only proceeds once the vitelline membrane formation is completed. The chorionic membrane is made up of an endochorion and an exochorion. Although the structural complexity of the follicular epithelium is maintained at 48 h PBM, its appearance at 60 h PBM is indicative of degenerative changes. By 60 h PBM synthesis of both the vitelline and chorionic membranes has been completed and vitellogenesis has ceased. This stage then represents the complete maturation of the ovum in C. theileri.