Structure of the insect oocyte nucleus with special reference to interchromatin granule clusters and cajal bodies

The nuclear structure of insect oocyte is described with reference to interchromatin granule clusters and Cajal bodies. It is suggested that the intranuclear structure is determined by the ovary organization and reflects the sources of oocyte RNA. Inactivated oocyte chromosomes in meroistic ovaries form a karyosphere, and their features are discussed. In insects with panoistic ovaries, the organization and molecular composition of complicated oocyte Cajal bodies are discussed, and the homology between a structure located inside Cajal bodies and interchromatin granule clusters is proved. Along with revealing some essential Cajal body components and factors involved in RNA polymerase II transcription, we analyze the absence of RNAP II itself from oocyte Cajal bodies of Acheta. In insects with meroistic ovaries, Cajal bodies of Drosophila and homology of Panorpa nuclear bodies to Cajal bodies and their peculiarities are described, because the nuclear bodies may share some features of both Cajal bodies and interchromatin granule clusters to represent a single nuclear domain.