POLYPEPTIDE HORMONE BIOSYNTHESIS--AMPHIBIAN MODELS

低分子量多肽激素的生物合成依赖于 一系列复杂的翻译后加工过程。 的 调节这些事件的加工酶被发现在不同的细胞中， ER/高尔基体/分泌颗粒网络的亚室。 理解 这些加工的表达、调节和细胞内途径 细胞器内的酶是建立一个清晰的理解的核心 关于分泌细胞的细胞生物学。 非哺乳动物内分泌研究 组织揭示了一系列的策略，这些策略已经进化到介导 多肽激素的生物合成。 将使用两栖模型系统 分析了阿黑皮素原（POMC）生物合成的两个方面， 与多肽生物合成途径相关的途径： 细胞内处理事件的分离，以及发育过程中的 加工酶的调节。 海洋蟾蜍为研究N- POMC产物α-MSH和β-内啡肽的乙酰化。 在 在哺乳动物中，这些反应在分泌颗粒中平行进行。 在无尾两栖类的中间脑垂体中，这些反应是 在时间和空间上都是分离的。 一系列的研究， 脉冲/追踪模式，免疫电镜，亚细胞分级 动力学分析将试图解释这种两栖动物 成功地分离了这些POMC终产物的N-乙酰化。 这些项目将提供深入了解的战略路线， 调节囊泡内的加工酶。 虎纹鱼幼鱼和幼鱼垂体前叶的研究 墨西哥钝口螈将研究 促肾上腺皮质激素的蛋白水解裂解。 促肾上腺皮质激素加工的发育转变 在两栖动物身上观察到的这一现象似乎是四足动物的共同特征 促皮质激素个体发育 两栖类脑垂体的研究为 模型研究促肾上腺皮质激素翻译后机制，并规避许多 胎鼠垂体模型系统的局限性。 ACTH- 由幼虫促皮质激素产生的相关裂解产物将 特征，以及这些产品对类固醇合成的影响， 将测定幼虫肾上腺细胞。

The biosynthesis of low molecular weight polypeptide hormones is dependent upon a complex sequence of posttranslational processing events. The processing enzymes that mediate these events are found within distinct subcompartments of the ER/golgi/secretory granule network. Understanding the expression, regulation and intracellular routing of these processing enzymes within organelles is central to establishing a clear understanding of the cell biology of secretory cells. Studies on non-mammalian endocrine tissues reveal the array of strategies that have evolved to mediate the biosynthesis of polypeptide hormones. Amphibian model systems will be used to analyzed two aspects of the Proopiomelanocortin (POMC) biosynthetic pathway that are relevant to polypeptide biosynthetic pathways in general: the segregation of processing events within cells, and the developmental regulation of processing enzymes. The toad, Bufo marinus, provides a unique model system to study the N- acetylation of the POMC products, alpha-MSH and beta-endorphin. In mammals, these reactions are performed in parallel in secretory granules. In the intermediate pituitary of anuran amphibians, these reactions are separated both temporally and spatially. A series of studies involving pulse/chase paradigms, immunoelectron microscopy, subcellular fractionation and kinetics analyses will attempt to explain how this amphibian has succeeded in segregating the N-acetylation of these POMC end products. These projects will provide insights into the strategies for routing and regulating processing enzymes within vesicles. Studies on the anterior pituitary of larval Ambystoma tigrinum and neotenic Ambystoma mexicanum will investigate developmental changes in the proteolytic cleavage of ACTH. The developmental shift in ACTH processing observed in amphibian appears to be a common feature of tetrapod corticotrope ontogeny. The amphibian pituitary studies provide convenient models for studying ACTH posttranslational mechanisms, and circumvent many of the limitations of the fetal rat pituitary model system. The ACTH- related cleavage products generated by larval corticotropes will be characterized, and the effects of these products on steroid synthesis by larval adrenal cells will be determined.