VITELLOGENESIS IN DECAPOD CEPHALOPODS - EVOLUTION OF OOCYTES AND FOLLICULAR CELLS DURING GENITAL MATURATION

  • 1 January 1976
    • journal article
    • research article
    • Vol. 65  (3) , 183-208
Abstract
During previtellogenesis in Sepia officinalis and Loligo vulgaris, the follicle cells (FC), originally arranged at the periphery of the oocyte form strands, through the axis of which runs a blood vessel. The follicle strands then move down into the ooplasm. They end up by occupying the greater part of the volume of the oocyte. At this stage, despite their increase in size, the FC do not undergo conspicuous cytological transformations. In the ooplasm, excepting a few specialized structures (annulate lamellae), there is no marked differentiation. The onset of vitellogenesis is characterized by the appearance in the ooplasm of paracrystalline elements. A zona pellucida appears between the oocyte and the FC, and yolk of a permanent type begins to accumulate at this point. Concurrently, the FC undergo characteristic reorganization: hypertrophy of the nucleolar mass, multiplication of granular reticulum cisternae, and increase in number and size of Golgi complexes. The saccules of the Golgi complex process a material rich in carbohydrate and protein bearing the same cytochemical characteristics as the yolk. In the basal zone of the FC, deep invaginations of the blood vessel walls scallop the cytoplasm. Immunofluorescence indicates a lack of immunological identity between blood and yolk proteins. Chorion formation is accompanied by a fresh transformation of FC.: the granular endoplasmic reticulum breaks up into rounded cisternae containing a dense material; the morphology of the Golgi complex is modified. The earliest chorion elements accumulate, first in the form of isolated lobules within the zona pellucida, later fusing to form a continuous layer bounding the FC microvilli. These cells eventually enter a degenerative phase and disappear, while the oocyte is set free by dehiscence into the coelom.

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