A study of the fine structure of the rabbit primary oocyte

Abstract

Primary oocytes in various stages of growth within the ovaries of sexually mature rabbits were observed with the electron microscope. The structural relationship between the oocyte and the follicle cells in primary and secondary follicles is briefly presented. The large nucleus of the primary oocyte has a dense granular nucleolus which assumes a reticular pattern. Pores are present in the nuclear membrane. The cytoplasm of the oocytes contains many Golgi complexes, inclusion bodies and RNP particles, numerous mitochondria, and only a few elements of endoplasmic reticulum. Modifications of mitochondrial fine structure occur as growth proceeds. The cristae arrangement elucidated in this study is unique to oocytes. Evidence for mitochondrial division is presented since dumbbell-shaped mitochondria are present. The significance of the abundance of mitochondria, and their configuration at certain stages in oocyte growth, is discussed. The Golgi complex is similar to that found in other cell types. Accumulations of numerous small vesicles in close association with the Golgi complexes are present in all stages of primary oocytes studied. Numerous, highly irregular lipid inclusions are present in the cytoplasm in close association with the mitochondria. Dilated vacuoles are a frequent component of the cytoplasm.