Vieira Simón, de Pérez Gloria Romero, Ramírez-Pinilla Martha Patricia
Departamento de Biología, Universidad Nacional de Colombia, Bogotá, Colombia.
J Morphol. 2010 Jun;271(6):738-49. doi: 10.1002/jmor.10830.
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.
我们研究了胎生营养型的美洲石龙子属安第斯蜥蜴卵巢卵泡的超微结构组织。初级卵泡的卵母细胞被单层卵泡细胞包围。在前卵黄发生阶段，这些细胞分层并分化为三种细胞类型：小的、中等的和大的球状、非梨形细胞。在前卵黄发生后期的卵泡中，卵泡细胞之间出现充满液体的间隙，这是细胞裂解的证据。在卵黄发生卵泡中，卵泡细胞构成具有大腔隙的单层颗粒层；它们细胞质的内容物释放到形成透明带的卵周间隙中。较年轻卵母细胞的卵膜呈现出初期的短突起；随着卵母细胞生长，这些突起组织成微绒毛表面。在卵黄发生过程中，微绒毛基部形成小管，通过内吞作用内化物质。在前卵黄发生早期卵泡的近核卵质中，巴尔比亚尼卵黄体作为细胞器和脂滴的聚集体被发现；在卵母细胞生长过程中，这种细胞器复合体分散在卵质中。在前卵黄发生后期，膜性细胞器在外周卵质中特别丰富，而在髓质卵质中则有丰富的囊泡和颗粒物质。卵黄发生卵泡的卵质显示出由丰富的膜性细胞器和许多囊泡体组成的外周带，其中一些囊泡体有小的脂蛋白核心。未观察到像卵黄营养型爬行动物那样有组织的卵黄小板。朝向髓质卵质，电子透明囊泡尺寸变大，含有正在溶解的细胞质物质残余。本研究结果表明该物种的卵泡与其他有鳞目动物之间存在结构相似性；然而，美洲石龙子成熟卵母细胞的卵质在形态上与有袋类动物成熟卵母细胞的卵质相似，这表明与胎生营养和微卵黄卵的进化相关的有趣进化趋同现象。
