Oogenesis in Fundulus heteroclitus IV. Yolk‐vesicle formation

Yolk vesicles first appear within the oocyte of Fundulus heteroclitus in association with elaborate smooth endoplasmic reticulum and Golgi elements. Cytochemistry indicates the yolk vesicles contain an acidic glycoconjugate. [3H]Glucose is used to examine the synthesis and accumulation of yolk vesicles in studies performed both in vivo and in vitro, since it is selectively incorporated into nascent yolk vesicles. The endogenous synthesis of yolk‐vesicle glycoconjugate is documented by autoradiography, gel electrophoresis, and fluorography. A large (> 200 kDa) glycoconjugate has been identified, which is thought to reside in yolk vesicles. Incorporation studies done in vitro substantiate that this putative yolk‐vesicle material is synthesized by the oocyte itself and that synthesis occurs not only during the so‐called yolk‐vesicle stage, but also throughout vitellogenesis and early maturation. The view is thus adopted that various synthetic and physiological events are sequentially initiated and subsequently remain active throughout oocyte growth.