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首页> 外文期刊>Cell and Tissue Research >Intra-epithelial spicules in a homosclerophorid sponge
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Intra-epithelial spicules in a homosclerophorid sponge

机译：同卵海绵中的上皮内针刺

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Attempts to understand the intricacies of biosilicification in sponges are hampered by difficulties in isolating and culturing their sclerocytes, which are specialized cells that wander at low density within the sponge body, and which are considered as being solely responsible for the secretion of siliceous skeletal structures (spicules). By investigating the homosclerophorid Corticium candelabrum, traditionally included in the class Demospongiae, we show that two abundant cell types of the epithelia (pinacocytes), in addition to sclerocytes, contain spicules intracellularly. The small size of these intracellular spicules, together with the ultrastructure of their silica layers, indicates that their silicification is unfinished and supports the idea that they are produced “in situ” by the epithelial cells rather than being incorporated from the intercellular mesohyl. The origin of small spicules that also occur (though rarely) within the nucleus of sclerocytes and the cytoplasm of choanocytes is more uncertain. Not only the location, but also the structure of spicules are unconventional in this sponge. Cross-sectioned spicules show a subcircular axial filament externally enveloped by a silica layer, followed by two concentric extra-axial organic layers, each being in turn surrounded by a silica ring. We interpret this structural pattern as the result of a distinctive three-step process, consisting of an initial (axial) silicification wave around the axial filament and two subsequent (extra-axial) silicification waves. These findings indicate that the cellular mechanisms of spicule production vary across sponges and reveal the need for a careful re-examination of the hitherto monophyletic state attributed to biosilicification within the phylum Porifera.
机译：难以理解和解释海绵中生物硅化的复杂性的原因是难以分离和培养其巩膜细胞，巩膜细胞是在海绵体内以低密度游荡的特化细胞，被认为是硅质骨骼结构分泌的唯一原因（针头）。通过调查传统上包括在类Demo皮中的同硬皮大叶皮质类固醇，我们显示了除了巩膜细胞外，两种丰富的上皮细胞类型（pinacocytes）（胞内）还包含针状细胞。这些细胞内针状体的小尺寸以及其二氧化硅层的超微结构，表明它们的硅化作用尚未完成，并支持了它们是由上皮细胞“原位”产生而不是从细胞间中磺酰基掺入的想法。还在巩膜细胞核和软骨细胞的细胞质内出现（尽管很少）的小刺的起源更加不确定。在这种海绵中，不仅位置而且针状结构都是不常规的。针头的横截面显示出一个亚圆形的轴向细丝，外部被二氧化硅层包裹，随后是两个同心的轴向外有机层，每个有机层依次被二氧化硅环包围。我们将这种结构模式解释为一个独特的三步过程的结果，该过程由围绕轴向细丝的初始（轴向）硅化波和随后的两个（轴向外）硅化波组成。这些发现表明针刺产生的细胞机制在海绵之间是不同的，并且表明需要仔细重新检查归因于孔菌属内生物硅化的迄今为止的单系统状态。

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