NUTRITIONAL MECHANISMS IN RAT EMBRYO AND FETUS

广泛的长期目标是发现更多关于细胞和 大鼠胚胎和胎儿营养供应的分子机制 妊娠中期和晚期，最终目的是确定营养 特别容易受到干扰的补给路线 先天缺陷和/或宫内发育迟缓。焦点 应用的关键是氨基酸和铁的输送，以及 具体目标是：1)确定氨基酸的细胞机制 植入后发育阶段对大鼠胚胎的补充 但在其被内脏卵黄囊包裹之前；2)测定 蛋白质和游离氨基酸在氨基酸供应中的相对重要性 酸对中、晚期妊娠大鼠胚胎的影响；3)测定 胎盘和内脏卵黄囊在胚胎发育中的作用 为妊娠中晚期的大鼠胎儿补充氨基酸；4) 大鼠内脏卵黄囊对转铁蛋白内吞作用的研究 在调节铁向胚胎输送中的作用，以及 胞饮作用的抑制剂对胚胎铁供应的影响。它有 此前有研究表明，9.5-至11.5-的氨基酸营养 日龄大鼠胚胎不是来自于游离氨基酸含量 母体血浆，但由于体内吞饮细胞蛋白的降解 内脏卵黄囊的细胞。还有几种诱导剂 先天缺陷在这个阶段给母亲用药 发育抑制胞饮作用或溶酶体内蛋白分解，以及 从而中断对胚胎的氨基酸供应。建议进行的实验 在本申请中，寻求确定(A)胞饮增多症和 母体蛋白的溶酶体分解代谢在数量上是重要的 早期和晚期胚胎/胎儿的氨基酸来源 与之前调查的结果相比，(B)是否有其他 重要的营养物质(如铁)通过这种途径提供。这个 将使用的技术包括胚胎培养，用于早期阶段， 以及后期的活体方法。各种放射性同位素 技术将部署在整个过程中，生化和 卵黄囊处理的研究将采用细胞化学方法。 转铁蛋白。建议的研究与人类有直接关系。 医药。在妊娠早期，卵黄囊是一个突出的 人类概念中的结构，以及在这方面可用的微不足道的数据 组织表明，它的细胞在形态上与 大鼠的卵黄囊因此可能起到类似的作用。尽管 人类卵黄囊在怀孕10到11周时退化，这些问题 我们试图回答关于血浆蛋白可能的贡献 与中近期胎儿的氨基酸营养有关 对人类来说。长期以来，人们一直认为母体游离氨基酸是 是胎儿唯一重要的氨基酸来源。测试这一点 假设早该发生了。

The broad long-term objective is to discover more about the cellular and molecular mechanisms of nutrient supply to the rat embryo and fetus in mid- and late-gestation with the ultimate aim of identifying nutrient supply routes that are particularly vulnerable to perturbations leading to congenital defects and/or intra-uterine growth retardation. The focus of the Application is the delivery of amino acids and iron, and the Specific Aims are: 1) To determine the cellular mechanisms of amino acid supply to the rat embryo at the stage of development after implantation but before its envelopment by the visceral yolk sac; 2) To determine the relative importance of proteins and free amino acids in supplying amino acids to the mid- to late-gestation rat fetus; 3) To determine the respective contributions of the placenta and visceral yolk sac in supplying amino acids to the mid- to late-gestation rat fetus; 4) To study the endocytosis of transferrin by the rat visceral yolk sac, its role in mediating the delivery of iron to the embryo, and the effect of inhibitors of pinocytosis on iron supply to the embryo. It has previously been shown that the amino acid nutrition of the 9.5- to 11.5- day rat embryo does not derive from the free amino acid content of the maternal plasma, but from the degradation of pinocytosed protein in the cells of the visceral yolk sac. Also that several agents that induce congenital defects when administered to the mother at this stage of development inhibit either pinocytosis or intralysosomal proteolysis, and thus interrupt amino acid supply to the embryo. The experiments proposed in this Application seek to determine (a) whether pinocytosis and lysosomal catabolism of maternal protein is a quantitatively important source of amino acids for the embryo/fetus at earlier and later stages of gestation than that previously investigated, and (b) whether other important nutrients (such as iron) are supplied by this route. The techniques to be used will include embryo culture, for the early stages, and in vivo methods for later stages. A variety of radioisotope techniques will be deployed throughout, and both biochemical and cytochemical methods will be used for the studies on yolk-sac handling of transferrin. The studies proposed are of direct relevance to human medicine. At the early stages of gestation the yolk sac is a prominent structure in the human conceptus, and the meager data available on this tissue indicate that its cells are morphologically similar to those of the rat yolk sac and may therefore play a similar role. Although the human yolk sac regresses at 10 to 11 weeks of gestation, the questions we seek to answer concerning the possible contribution of plasma protein to the amino acid nutrition of the mid- to near-term fetus are pertinent to the human. It has long been assumed that maternal free amino acid is the only significant source of amino acids for the fetus. Testing this assumption is overdue.