A storage form of ribosomes in mouse oocytes

By utilizing the technique of whole mount electron microscopy, large numbers of very highly ordered lattice-like structures have been observed in mouse oocyte preparations, and thin-section studies have shown that these structures are of cytoplasmic origin. In some preparations, there appeared to be a breakdown of the lattice with the release of particles having the dimensions of ribosomes (225 Å). This evidence, together with the results of enzyme digestion studies which show that the lattices are composed of RNA and protein, leads to the conclusion that these structures are highly ordered aggregates of ribosomes. The ribosomes are strung together to form chains which are capable of regular cross-linking with adjacent chains to form the characteristic lattice. It is suggested that the ribosomes are held together by basic proteins and are stored in an inactive form within the lattice until after fertilization, when they will be released and used in protein synthesis during early cleavage, until the embryo makes its own functional ribosomes. This premise is discussed in relation to the appearance and disappearance of the lattice, the synthesis of ribosomal RNA, the existence of ribosome inactivating proteins, and the possible formation of inactive maternal ribosome-mRNA complexes during oocyte maturation.