Ovarian follicle development during vitellogenesis in the house cricket Acheta domesticus

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Abstract
To determine the morphological correlates of vitellogenin uptake and distribution, vitellogenic ovarian follicles of Acheta domesticus were examined by light and transmission electron microscopy. Yolk deposition was usually restricted to the terminal follicle of each panoistic ovariole, but if the terminal follicle had completed vitellogenesis and had not yet been ovulated, the penultimate follicle was often vitellogenic. Vitellogenesis occurred only in the ovaries of adults, with follicles representing all stages of vitellogenic development occurring simultaneously within a single ovary. Vitellogenic follicles were 0.75 to >2.0 mm long. The single irregularly shaped nucleus of each follicle cell contained two to three nucleoli. During vitellogenesis the epithelium of individual follicles progressed from columnar to cuboidal to squamous. The distribution of cytoplasmic organelles within individual follicle cells was polarized during early and middle stages of vitellogenesis. Near the end of vitellogenesis, polarity disappeared, the follicular epithelium became squamous, and the frequency of vesicular and multivesicular bodies in the follicle cell cytoplasm increased. A well-developed capability for follicle cell protein synthesis and secretion throughout vitellogenesis was indicated by abundant rough endoplasmic reticulum and Golgi bodies. Receptor-mediated endocytotic activity by the follicle cells during all stages of vitellogenesis was suggested by omnipresent coated pits on all surfaces. Septate junctions, gap-like junctions, and desmosomes all occurred in the lateral membranes, while gap-like junctions predominated at the oocyte–follicle cell interface. In follicles longer than 1 mm, adjacent follicle cells were separated by intercellular channels that widened to as much as 10 m̈m by the completion of vitellogenesis. The channels contained a flocculent material, and a similar-appearing material filled the space between the oolemma and follicle cell apical membranes. The oolemma contained a profusion of coated pits throughout vitellogenesis.

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