title: The origin of protein and fatty yolk in Rana pipiens. IV. Secondary vesicular yolk formation in frog oocytes.
abstract: Secondary yolk precursor complexes are differentiated from primary yolk precursor complexes in that little or no background matrix or small vesicles are present and that electron-dark, amorphous yolk protein fills the precursor at a very early stage of growth. Secondary precursors are formed in two ways; from multivesicular bodies or from the fusion of smooth-surfaced endocytotic vesicles. Ultimately, fusion of secondary precursors with multivesicular bodies makes them indistinguishable from primary precursors. Precursors are called yolk platelets when they are mainly crystalline with only a small amount of amorphous yolk protein present. The structure of the crystal is particulate with a spacing of 70--85 A. At high resolution, the particles are seen to measure approximately 20 X 60 A. The chemical composition and interpretations of studies of the crystal structure are discussed.
mesh_terms: D000818:Animals; D001001:Anura; D003460:Crystallization; D004527:Egg Proteins / Q000032:analysis*; D004530:Egg Yolk; D004705:Endocytosis; D005260:Female; D009865:Oocytes / Q000032:analysis / Q000648:ultrastructure*; D009940:Organoids / Q000502:physiology / Q000648:ultrastructure; D010063:Ovum / Q000648:ultrastructure*; D011894:Rana pipiens
chemical_list: D004527:Egg Proteins