Ultrastructure of oocytes of the shrimp, Penaeus vannamei: Cortical specialization formation

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Ovaries of the South American white shrimp, Penaeus vannamei, undergo pronounced ultrastructural changes during development. In pre-vitellogenic oocytes, the cytoplasm is relatively devoid of structure except for abundant ribosomes. In oocytes about midway through development, three types of cytoplasmic vesicles become abundant, and cortical specializations appear to lie outside the highly invaginated oolemma. Late in oocyte development, the cytoplasmic matrix becomes quite dense and several types of vesicles become prominent in the cortex. The cortical specializations appear to complete maturation outside the oolemma. Follicle cells that surround the oocytes at mid to late development have prominent nuclei, nucleoli, and stacks of rough endoplasmic reticulum. Use of a monospecific antibody to a cortical specialization polypeptide demonstrated that the dilated endoplasmic reticulum as well as the growing cortical specializations of mid-cycle oocytes were immunoreactive, suggesting that this polypeptide is synthesized within the oocytes. In nearly mature oocytes, immunoreactivity appears to be restricted to the cortical specializations. Use of antibodies to a yolk polypeptide indicated presence of this polypeptide in the moderately dense (yolk) cytoplasmic vesicles, the cortical specializations, and the perivitelline space.