Evolution of Placental Calcium Transport in Reptiles

陆栖脊椎动物有两种基本的生殖方式：胎生，即活仔的出生;卵生，即胚胎在雌性体外发育的产卵。所有的哺乳动物，除了单孔目动物，都是胎生的。海龟、鳄鱼和鸟类都是卵生动物。相比之下，有鳞爬行动物（蛇和蜥蜴）显示出多样性的生殖模式，大约20%是胎生的，至少有三个物种是繁殖双峰。有鳞动物的胎生已经独立进化了100多次，胎生的进化与胚胎营养模式从强化鸡蛋中的能量储存到胎盘营养交换的转变有关。所有的脊椎动物胚胎都需要钙才能成功发育。卵生物种胚胎钙供应的来源和模式与胎生物种不同。卵生物种的胚胎从蛋黄和蛋壳中获得钙，这些钙来源于卵黄发生和产卵前的脱壳过程中。胎生胚胎从卵黄中获得一些钙，但在发育后期也依赖胎盘转移。 钙转运到胚胎的时间、来源和机制是否会影响导致胎生的进化创新的潜力？本项目将探讨在陆生脊椎动物中生殖模式多样性最高的一个谱系（有鳞爬行动物）中，胚胎钙供应模式与生殖模式（产卵或活产）之间的关系。 将比较所选卵生和胎生有鳞动物胚胎钙供应的模式和机制，以建立胎盘钙转运演变的模型。 该项目将比较子宫钙分泌的时间和机制以及胚胎钙动员的时间和机制：1）两个最近进化胎生的物种，2）胎盘钙运输很少的胎生物种，3）严重依赖胎盘钙的胎生物种。 将研究密切相关的产卵物种以进行比较。 原子吸收光谱法将用于确定胚胎钙吸收的模式。 通过免疫印迹和免疫组织化学方法确定钙转运蛋白calbindin-D28 K、Ca 2 +-ATPase的发育表达，研究子宫和胚胎膜中钙转运的时间和机制。 这项研究将有助于通过研究高度保守的向胚胎输送营养物质的机制，更好地了解陆生脊椎动物的胚胎发育。 该项目将整合研究和教育，为来自主要本科部门的本科生提供在博士研究环境中的机会。授予部门。 来自社会弱势群体的本科生将通过与罗纳德E.麦克奈尔学者计划在校园里。 这些努力将针对任何机构的任何合格的本科生。 这些学生将接受培训，旨在提高他们在研究生课程未来成功的潜力。

Terrestrial vertebrates exhibit two basic modes of reproduction; viviparity, or the birth of live young, and oviparity, or the laying of eggs in which embryonic development occurs outside the body of the female. All mammals, with the exception of monotremes, are viviparous. Turtles, crocodilians and birds are exclusively oviparous. In contrast, squamate reptiles (snakes and lizards) show a diversity of reproductive patterns with approximately 20% being viviparous and at least three species being reproductively bimodal. Viviparity in squamates has evolved independently more than 100 times and the evolution of viviparity is associated with a transition in the pattern of embryonic nutrition from fortification of energy stores in the egg to placental nutrient exchange. All vertebrate embryos require calcium for successful development. The source and pattern of calcium provision to embryos of oviparous species differs from that of viviparous species. Embryos of oviparous species derive calcium from yolk and eggshell, sources laid down during vitellogenesis and shelling prior to egglaying. Viviparous embryos derive some calcium from yolk but depend also on placental transfer late in development. Does the timing, source and mechanism of calcium transport to embryos influence the potential for evolutionary innovations leading to viviparity? This project will explore the relationship between the pattern of embryonic calcium provision and reproductive mode (egg-laying or live-bearing) in a lineage (squamate reptiles) that exhibits the highest diversity of reproductive patterns among terrestrial vertebrates. The pattern and mechanism of calcium provision to embryos of selected oviparous and viviparous squamates will be compared to develop a model for the evolution of placental calcium transport. The project will compare the timing and mechanism of calcium secretion by the uterus and the timing and mechanism of calcium mobilization by embryos of: 1) two species that have recently evolved viviparity, 2) a viviparous species with little placental calcium transport, and 3) a viviparous species that is heavily dependent on placental calcium. Egg-laying species that are closely related will be studied for comparison. Atomic absorption spectroscopy will be used to define the pattern of calcium uptake by embryos. The timing and mechanism of calcium transport in the uterus and embryonic membranes will be studied by defining the developmental expression of the calcium transporting proteins, calbindin-D28K, Ca2+-ATPase, using immunoblotting and immunohistochemistry. This research will contribute a greater understanding of embryonic development of terrestrial vertebrates through study of a highly conserved mechanism for delivery of nutrients to embryos. The project will integrate research and education by providing opportunities for undergraduate students from predominantly undergraduate departments in the research environment of a Ph.D. granting department. Undergraduate students from underrepresented segments of society will be actively recruited through collaboration with administrators of the Ronald E. McNair Scholars Program on campus. These efforts will target any eligible undergraduate from any institution. These students will receive training with an aim to increase their potential for future success in graduate programs.