Ultrastructure of the ovarian follicles in the placentotrophic Andean lizard of the genus Mabuya (Squamata: Scincidae)

Abstract

We studied the ultrastructural organization of the ovarian follicles in a placentotrophic Andean lizard of the genus Mabuya. The oocyte of the primary follicle is surrounded by a single layer of follicle cells. During the previtellogenic stages, these cells become stratified and differentiated in three cell types: small, intermediate, and large globoid, non pyriform cells. Fluid-filled spaces arise among follicular cells in late previtellogenic follicles and provide evidence of cell lysis. In vitellogenic follicles, the follicular cells constitute a monolayered granulosa with large lacunar spaces; the content of their cytoplasm is released to the perivitelline space where the zona pellucida is formed. The oolemma of younger oocytes presents incipient short projections; as the oocyte grows, these projections become organized in a microvillar surface. During vitellogenesis, cannaliculi develop from the base of the microvilli and internalize materials by endocytosis. In the juxtanuclear ooplasm of early previtellogenic follicles, the Balbiani's vitelline body is found as an aggregate of organelles and lipid droplets; this complex of organelles disperses in the ooplasm during oocyte growth. In late previtellogenesis, membranous organelles are especially abundant in the peripheral ooplasm, whereas abundant vesicles and granular material occur in the medullar ooplasm. The ooplasm of vitellogenic follicles shows a peripheral band constituted by abundant membranous organelles and numerous vesicular bodies, some of them with a small lipoprotein core. No organized yolk platelets, like in lecithotrophic reptiles, were observed. Toward the medullary ooplasm, electron-lucent vesicles become larger in size containing remains of cytoplasmic material in dissolution. The results of this study demonstrate structural similarities between the follicles of this species and other Squamata; however, the ooplasm of the mature oocyte of Mabuya is morphologically similar to the ooplasm of mature oocytes of marsupials, suggesting an interesting evolutionary convergence related to the evolution of placentotrophy and of microlecithal eggs.

Histological and immunohistochemical study of the ovaries and oviducts of the juvenile female of Caiman latirostris (Crocodilia: Alligatoridae)

“…Previtellogenesis is a stage of development that involves emergence of a variety of follicles, ranging from primordial follicles that have recently migrated out of the germinal bed to large follicles immediately prior to vitellogenesis (VIEIRA et al 2010). The previtellogenic follicles of C. latirostris are abundant and contain a nucleus, ooplasm and a layer of follicular or granulosa cells.…”

Gonadal Differentiation in Reptiles Exhibiting Environmental Sex Determination

“…Initially, follicles possess a single granulosa layer, but during previtellogenic development, the follicular layer differentiates into 3 cell types: small, intermediate and pyriform cells [Uribe et al, 1996;Gómez and Ramírez-Pinilla, 2004]. Most notable in the polymorphic stage of squamate follicular cells is the consistent development of large clear pyriform cells; however, the morphology of these pyriform cells varies between species [Vieira et al, 2010]. These cells possess distinctive cytoplasmic projections that cross the notched zona pellucida and directly connect the pyriform cells with the oocyte cytoplasm.…”

Ultrastructural and histochemical study of previtellogenic oogenesis in the desert lizard Scincus mitranus (Squamata, Sauropsida)

“…The structure of the granulosa in reptilian sauropsids varies between groups: Testudines (turtles), Sphenodontida, Squamata (lizards and snakes), and crocodiles (Arrieta, Sandova, & Alvarez, ; Hernandez‐Franyutti, Uribe‐Aranzabal, & Guillette, ; Machado‐Santos, Santana, Vargas, Abidu‐Figueiredo, & de Brito‐Gitirana, ; Vieira, Perez, & Ramırez‐Pinilla, ). In crocodiles, sphenodon, and turtles, the granulosa layer remains as a single layer of small cells throughout follicle development (Narbaitz, 1973; Hubert, ).…”

“…The ultrastructure of oogenesis of lizards has been described in few species, including Zootoca vivipara (Hubert, ), Lacerta sicula (Filosa & Taddei, ), Acanthodactylus scutellatus (Bou‐Resli, ), and Elgaria coerulea (Klosterman, ). Notably, relatively few species of squamates have been studied (Vieira et al, ), including the family Scincidae, the largest family of lizards. The presence of both oviparous and ovoviviparous species in this family indicates the presence of corresponding diversity of the granulosa and oocyte structures.…”