Wilt Fred H, Killian Christopher E, Hamilton Patricia, Croker Lindsay
Department of Molecular and Cell Biology, University of California, 142 Life Sciences Addition, Berkeley, CA 94720-3200, USA.
Exp Cell Res. 2008 May 1;314(8):1744-52. doi: 10.1016/j.yexcr.2008.01.036. Epub 2008 Mar 10.
Skeleton formation involves secretion of massive amounts of mineral precursor, usually a calcium salt, and matrix proteins, many of which are deposited on, or even occluded within, the mineral. The cell biological underpinnings of this secretion and subsequent assembly of the biomineralized skeletal element is not well understood. We ask here what is the relationship of the trafficking and secretion of the mineral and matrix within the primary mesenchyme cells of the sea urchin embryo, cells that deposit the endoskeletal spicule. Fluorescent labeling of intracellular calcium deposits show mineral precursors are present in granules visible by light microscopy, from whence they are deposited in the endoskeletal spicule, especially at its tip. In contrast, two different matrix proteins tagged with GFP are present in smaller post-Golgi vesicles only seen by electron microscopy, and the secreted protein are only incorporated into the spicule in the vicinity of the cell of origin. The matrix protein, SpSM30B, is post-translationally modified during secretion, and this processing continues after its incorporation into the spicule. Our findings also indicate that the mineral precursor and two well characterized matrix proteins are trafficked by different cellular routes.
骨骼形成涉及大量矿物质前体（通常是钙盐）和基质蛋白的分泌，其中许多基质蛋白沉积在矿物质上，甚至被包裹在矿物质内部。这种分泌以及随后生物矿化骨骼元素组装的细胞生物学基础尚未得到充分理解。我们在此探讨海胆胚胎初级间充质细胞（即沉积内骨骼骨针的细胞）内矿物质和基质的运输与分泌之间的关系。细胞内钙沉积物的荧光标记显示，矿物质前体存在于光镜可见的颗粒中，它们从这些颗粒中沉积到内骨骼骨针中，尤其是在骨针的尖端。相比之下，两种用绿色荧光蛋白标记的不同基质蛋白仅存在于电子显微镜下才能看到的较小的高尔基体后囊泡中，并且分泌的蛋白仅在起源细胞附近被整合到骨针中。基质蛋白SpSM30B在分泌过程中进行翻译后修饰，并且在其整合到骨针后这种加工仍在继续。我们的研究结果还表明，矿物质前体和两种特征明确的基质蛋白通过不同的细胞途径进行运输。
