Intracellular calcium compartmentation in the mineral forming organisms Porcellio scaber (Crustacea), Magellania venosa (Brachiopoda) and Emiliania huxleyi (Haptophyta).

生物碳酸盐的形成是生物圈中最重要的过程之一。它导致了大量石灰岩沉积物的形成，这些沉积物是大气中二氧化碳的重要汇。壳形成的细胞机制涉及钙通过细胞运输到矿化部位。这种转运既可以以离子的形式发生，也可以作为细胞内形成的无定形矿物前体相发生。在这两种情况下，运输都必须在细胞器内进行，以避免细胞质中毒性高的钙离子浓度。然而，我们对生物矿化过程中细胞内钙区隔的了解是零碎的。特别是，囊泡结构和内质网被认为有助于钙的运输。此外，所涉及的细胞器类型可以根据生物体和矿化组织而变化。因此，我们计划研究钙在生物矿化细胞内的亚细胞分布，目的是确定有助于钙运输的细胞器。为了解释生物体和组织之间可能存在的差异，计划研究五种不同的细胞系统。他们三个从陆地甲壳纲动物Porcellio痂:1)前胸骨上皮,在运输期间利率特别是高钙碳酸钙的形成和吸收座大型水库,2)的真皮部分incisivae下颚,磷酸氢钙形成的作为一个例子,和3)的肝胰腺上皮细胞,动物摄入后其蜕皮,传输的矿物CaCO3-containing蜕皮血淋巴。在这里，特别有趣的是，一种细胞类型在溶酶体颗粒中积累重金属，提高了这些细胞也参与钙运输的可能性。此外，4)拟对腕足动物麦哲伦（Magellania venosa）和海洋球囊藻埃米利亚（Emiliania huxleyi）的套上皮进行研究。腕足类动物早在寒武世就存在，分布在世界各地。在那里，化石壳代表了一个巨大的同位素特征档案，这对重建古气候因素很重要，但也可能受到细胞机制的影响。赫胥黎菌占海洋CaCO3产量的三分之一，是胞内细胞器内方解石形成的一个例子。对于样品制备，将使用高压冷冻和超低温切片。结构方面和钙的分布将通过冷冻扫描电子显微镜，电子探针显微分析和能量过滤透射电子显微镜进行分析。本研究的目的是获得生物矿化过程中细胞钙转运机制及其在进化过程中的功能多样性和保护的新见解。

Formation of biogenic carbonates is one of the most important processes in the biosphere. It has led to the formation of vast limestone deposits representing an important sink for atmospheric CO2. The cellular mechanisms of shell formation involve the transport of calcium through cells to the site of mineralisation. This transport may occur either in the form of ions or as an amorphous mineral precursor phase formed within the cells. In both cases, transport has to take place within cell organelles to avoid high toxic calcium-ion concentrations in the cytosol. However, our knowledge on intracellular calcium compartmentation during biomineralisation is fragmentary. In particular, vesicular structures and the endoplasmatic reticulum have been suggested to contribute to the calcium transport. In addition, the type of organelles involved can vary, depending on the organism and mineralized tissue. Therefore, we plan to investigate the subcellular distribution of calcium within biomineralising cells, with the aim to identify the organelles contributing to calcium transport. To account for possible differences between organisms and tissues, it is planned to investigate five different cell systems. Three of them from the terrestrial crustacean Porcellio scaber: 1) the anterior sternal epithelium, in which calcium transport rates are notably high during formation and resorption of large calcium carbonate reservoirs, 2) the hypodermis of the partes incisivae of the mandibles, as an example of calcium phosphate formation, and 3) the epithelium of the hepatopancreas that, after the animal has ingested its exuviae, transports mineral from the CaCO3-containing exuviae to the hemolymph. Here, it is of particular interest that one cell type accumulates heavy metals within lysosomal granules, raising the possibility that these are also involved in calcium transport. Furthermore, 4) it is planned to investigate the mantle epithelium of the brachiopod Magellania venosa, and 5) the marine coccolithophorid alga Emiliania huxleyi. Brachiopods exist from the early Cambrium with world wide geographic distribution. There fossil shells represent an immense archive for isotope signatures, that are important for reconstruction of paleo-climatic factors and that, however, can be influenced by cellular mechanisms. Emiliania huxleyi is responsible for one third of the marine CaCO3 production, and is an example of calcite formation within an intracellular organelle.For sample preparation high pressure freezing and cryo-ultramicrotomy will be used. Structural aspects and the distribution of calcium will be analysed by cryo-scanning electron microscopy, electron probe microanalysis and energy filtered transmission electron microscopy. The aim of the proposed investigations is to attain new insights in the mechanisms of cellular calcium transport in biomineralisation and its functional diversity and conservation during evolution.