Blackburn Daniel G, Gavelis Gregory S, Anderson Kristie E, Johnson Amy R, Dunlap Kent D
Department of Biology and Electron Microscopy Facility, Trinity College, Hartford, Connecticut 06106, USA.
J Morphol. 2010 Oct;271(10):1153-75. doi: 10.1002/jmor.10860.
The lizard Sceloporus jarrovi (Phrynosomatidae) is one of the most widely studied viviparous reptiles of North America. Past research has assumed that placentation in this species is relatively simple and functions mainly in gas exchange. Our examination of the late stage placenta via transmission electron microscopy reveals that S. jarrovi has a unique combination of placental characteristics, with unusual specializations for secretion and absorption. In the chorioallantoic placenta, chorionic and uterine tissues are directly apposed through eggshell loss, and their epithelia are greatly attenuated, enhancing gas exchange; this placenta shows evidence of both nutrient transfer and endocrine function. Contrary to past inferences, a yolk sac placenta forms from the avascular omphalopleure and persists through the end of gestation. The uterine epithelium is enlarged and secretory, and the fetal omphalopleure shows branching absorptive channels and other specializations for uptake. Elsewhere, the omphalopleure develops elongated folds that protrude into a coagulum of degenerating shell membrane and other organic material. Uterine tissue in this region shows specializations for absorption. Placental features in S. jarrovi have unexpected functional implications, and challenge assumptions that specializations for nutrient transfer are confined to matrotrophic species.
蜥蜴斯氏强棱蜥（角蜥科）是北美地区研究最为广泛的胎生爬行动物之一。过去的研究认为，该物种的胎盘相对简单，主要功能是气体交换。我们通过透射电子显微镜对晚期胎盘进行检查后发现，斯氏强棱蜥具有独特的胎盘特征组合，在分泌和吸收方面有不同寻常的特化。在绒毛膜尿囊胎盘里，绒毛膜和子宫组织通过蛋壳消失而直接贴合，它们的上皮细胞大幅变薄，增强了气体交换；这个胎盘显示出营养物质转移和内分泌功能的证据。与过去的推断相反，卵黄囊胎盘由无血管的卵黄膜形成，并持续到妊娠期结束。子宫上皮细胞增大且具有分泌功能，胎儿的卵黄膜显示出分支状的吸收通道以及其他用于摄取的特化结构。在其他地方，卵黄膜形成细长的褶皱，伸入退化的壳膜和其他有机物质的凝块中。该区域的子宫组织显示出吸收特化结构。斯氏强棱蜥的胎盘特征具有意想不到的功能意义，并对营养物质转移特化仅限于母性营养物种的假设提出了挑战。
