Actin Is a Major Structural and Functional Element of the Egg Cortex of Giant Silkmoths during Oogenesis

The cortex and subcortical regions of the developing follicles and eggs of silkmoths are rich in cytoskeletal elements, particularly actin. In situ analysis using [ 3H]-polyuridylic acid and biotinylated oligo d(T) reveals a pattern of changes in poly(A) + RNA distribution during oogenesis. The developing pattern of distribution of actin filaments in the ooplasm closely resembles that of poly(A) + RNA. RNA polymerase II is also associated with the cortical cytoskeleton. Destruction of the actin filaments in the developing oocytes by cytochalasin D randomizes the distribution of mRNA and causes the displacement of RNA polymerase II from the cortex. Rhodamine-conjugated phalloidin and a monoclonal antibody against cytoskeletal actin were used in combination with laser scanning confocal microscopy to examine the details of actin distribution in the oocytes. RNA polymerase II was located in developing oocytes using both anti- Drosophila RNA polymerase II antibody and fluorescein-conjugated amanitin.