Oogenesis in Fundulus heteroclitus. V. The relationship of yolk vesicles and cortical alveoli

Yolk vesicles, which first appear in small oocytes, are morphologically indistinguishable from cortical alveoli, which are present in eggs. Both types of membrane‐limited vesicles show identical staining properties with both classical dyes for acidic glycoproteins and with fluorescein‐labeled lectins for specific carbohydrate moieties. Lectin ( Dolichos biflorus agglutinin)‐affinity chromatography was used to isolate from yolk vesicle‐stage follicles a > 200‐kilodalton (kDa) glycoconjugate that had been shown previously to be synthesized within the oocyte and to reside within yolk vesicles. Antiserum was prepared against the > 200‐kDa glycoconjugate and was used on immunoblots to demonstrate the presence of a substance both in yolk vesicle‐stage follicles and eggs that was immunoreactive. Indirect immunolabeling of plastic sections of various size follicles and eggs demonstrated that the antibody reacted with a substance found only in yolk vesicles and cortical alveoli. Thus, a combination of approaches (morphological, biochemical, and immunological) have been used to confirm the earlier cytological observations that suggested that yolk vesicles of small oocytes give rise to cortical alveoli of eggs. We suggest, therefore, that the term “yolk vesicle” is a misnomer since these structures, when mature, ultimately release their contents into the perivitelline space at fertilization, rather than serve as a source of nutrients for the embryo.