Cytodifferentiation in the Rana pipiens oocyte : I. Association between mitochondria and nucleolus-like bodies in young oocytes

Abstract

Small oocytes (approximately 125 μ in diameter) in adult Rana pipiens contain a number of cytoplasmic bodies which resemble nucleoli in size, shape, and staining reactions. These cytoplasmic nucleolus-like bodies are, however, more finely granular than nucleoli. The nucleolus-like bodies are surrounded by “satellite” bodies, “cytoplasmic cyclinders”, both “empty” and “yolk-containing” vesicles, and numerous mitochondria. Some of the mitochondria associated with the nucleolus-like bodies have small deposits of intracristal, crystalline yolk protein. The nucleolus-like bodies appear to contain thin filaments as well as small granules (40–80 A) as are also apparent in some of the associated mitochondria. Filaments are also present between the inner and outer mitochondrial membranes at a point where the mitochondria abut upon the nucleolus-like bodies; this condition may reflect an exchange mechanism. Structural variations in the nucleoli of young oocytes are also described. The possible significance of the observations in terms of informational exchange between the nucleus and cytoplasm and mitochondrial function in the frog oocyte is discussed.