Ultrastructure of developing ovarian follicles and ovulation in the lizard Anolis carolinensis (Reptilia)

Autor: Paul C. Schroeder, Laura J. Laughran, John H. Larsen
Rok vydání: 1981
Předmět:
Zdroj: Zoomorphology. 98:191-208
ISSN: 1432-234X
0720-213X
DOI: 10.1007/bf00312049
Popis: The ultrastructure of Anolis carolinensis ovarian follicles has been studied from early development (follicle 0.3 mm in diamter) through ovulation (∼8 mm in diamter). Cells of the surface epithelium, which change from cuboidal to squamous as the oocyte grows, contain filaments (7–9 nm in diameter) organized into bundles and oriented parallel to the long axis of the cell. The filaments are often associated with basal densities (∼50 nm thick and as much as 4.7 μm in length). In the fibroblasts of the thecal layer, two filament classes (4.5 nm and 9.0 nm) form networks in the cytoplasm. These filamentous bundles are often associated with densities adjacent to the basal plasmalemma; intermediate junctions may connect apposing cells. During previtellogenesis, the granulosa (follicle) cell layer includes three types of cells: 1) small, 2) intermediate, and 3) pyriform cells. The latter are joined to the oocyte by intercellular bridges that apparently provide an avenue for the transfer of ribosomes and other materials to the oocyte. Prior to vitellogenesis the small apical cells degenerate; the pyriform cells accumulate lipid-like droplets and whorls of filaments ∼12 nm thick, and then they also disappear. The contents of the latter cells are apparently transferred to the oocyte via intercellular bridges and/or by pyriform cell blebbing followed by oocyte endocytosis. At the start of vitellogenesis, the membrana granulosa consists of only a single layer of small cells whose pleomorphic macrovilli are attached to the oocyte by adhering zonules. During ovulation the granulosa cell macrovilli lose their connections with the oocyte surface and withdraw while the oocyte microvilli remain extended into the zona pellucida. After ovulation, the surface epithelial and thecal cells are cuboidal in shape and their nuclei are crenulated, suggesting cell contraction. The zona pellucida (fertilization coat), separated into two distinct layers and raised above the oocyte microvilli, encapsulates the ovulated egg.
Databáze: OpenAIRE
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