Ultrastructure of the oocytes of the Egyptian sping mouse (Acomys cahirinus)

The oocytes of types 2, 3, 4 and 5 follicles from the normal spiny mouse were examined withe the electron microsome. Multiple juxtanuclear Golgi bodies, mitochondria associated with flattened granular endoplasmic reticulum, and large nucleus are the main features of the type 2 follicle oocyte. The numbers of mitochondria and Golgi apparati increase significantly at later stages. Small mitochondrial aggregates lacking "intermitochondrial cement" are seen in the ooplasm of types 3, 4 and 5 follicles. "Lamellar complexes" comprising two to six elongate flattened rough ER cisternae and intercisternal filaments begin to appear in the occyte of the type 3 follicle. The intercisternal filaments may be observed as punctate-, dashed-, and solid-lines in cross sections. In tangential sections the filaments display a paracrystalline structure. In the type 4 follicle oocytes, the "lamellar complex" becomes more extensive; polysomes and ribosomal fibrils are juxtaposed to the "lamellar complexes." Bundles of ribosomal fibrils are abundant in the ooplasm of the type 5 follicle. The origin of ribosomal filaments and the functional significance of "lamellar complexes" are discussed.