Histological structure and histochemical characterization of the previtellogenic ovarian follicles in the Saudi Schmidt’s fringe-toed lizard Acanthodactylus schmidti (Squamata, Lacertidae) during breeding season

The ovarian structure and previtellogenic follicular development were studied in the lacertid lizard Acanthodactylus schmidti ( A. schmidti ) during the breeding season. The histochemical profiles of glycogen, acid mucopolysaccharides, proteins, lipids, and the alkaline phosphatase (ALP) activity in the growing ovarian follicles were also characterized. A single germinal bed per ovary was identified containing clusters of oogonia, naked oocytes, and primordial follicles. The ovary harbors numerous follicles of various sizes set inside its central lumen at different stages of development. During the transitional previtellogenic stage, the oocytes (120 to less than 1000 μm in diameter) appear surrounded by the granulosa, which is multilayered and polymorphic (up to 40 ± 2.5 μm in thickness). The granulosa layer comprises three distinguishable cells, small, intermediate, and pyriform cells. The theca is formed during this stage around the developing follicles as a thin layer of theca cells (4 ± 0.52 to 14 ± 1.3 μm). During the late previtellogenic stage, the size of oocytes is significantly increased ranging from 1000 to about 2000 μm. The multilayered granulosa layer significantly decreases in thickness (9 ± 0.8 μm) by the end of this stage and eventually reverts to one or two layers of regressing granulosa cells. In contrast, the thecal layer increases significantly in thickness (up to 16 ± 1.5 μm; P < 0.05) with advanced previtellogenesis. Small yolk granules begin to appear at the periphery of the ooplasm of oocytes of ∼ 2000 μm in diameter. The early vitellogenic stage became established in oocytes of ∼ 2500 μm in diameter, where the yolk granules were seen almost distributed throughout the whole ooplasm. The results also demonstrated changes in the amount and patterns of distribution of carbohydrates, lipids, and proteins, as well as ALP activity in the follicles, which are dependent on the stage of previtellogenic development. Such changes reflect the dynamic functional capacity of follicular cells in follicular development and oocyte growth. The functional implications of the present findings are discussed.