Pisam M, Jammet C, Laurent D
Département de Biologie Joliot Curie, CEA Saclay, 91191 Gif-sur-Yvette CEDEX, France.
Cell Tissue Res. 2002 Nov;310(2):163-8. doi: 10.1007/s00441-002-0622-z. Epub 2002 Sep 7.
The first steps of otolith formation were studied by electron microscopy in zebrafish embryos at different postfertilization (PF) time intervals. Between 19 and 22 h PF, the otic cavity contains glycogen particles derived by an apocrine process from the apical portions of the epithelial cells of the inner ear. The particles are arranged in parallel arrays, then in pseudocrystalloid structures, and finally in concentric arrays to form dense clusters referred to as "spherules". At 23 h PF, a group of "globules", consisting of modified aggregated "spherules" surrounded by several free "spherules", forms the nascent otolith. At 30 h PF, fused globules form a roughly spherical otolith. Spherules undergoing their process of modification and aggregation, are located in its central part, and constitute the so-called "nucleus". At 50 h PF, the otolith is a flattened hemisphere. It is made up of fused globules surrounded by two concentric layers whose organization is similar to that observed in the otolith of the adult fish. At this stage, calcium may be detected in the otolith except in its nucleus. We suggest that glycogen molecules found in the nascent otolith might allow the insertion of molecules such as glycoproteins (collagens) which are known to fix calcium. As a result, glycogen might play a key role in initiating the formation of otoliths and possibly that of other calcified tissues.
通过电子显微镜对不同受精后（PF）时间间隔的斑马鱼胚胎耳石形成的最初步骤进行了研究。在受精后19至22小时之间，耳腔中含有通过顶浆分泌过程从内耳上皮细胞顶端部分衍生而来的糖原颗粒。这些颗粒先排列成平行阵列，然后形成假晶体结构，最后形成同心阵列以形成称为“小球体”的致密簇。在受精后23小时，一组“小球”形成了新生耳石，它由被几个游离“小球体”包围的经过修饰的聚集“小球体”组成。在受精后30小时，融合的小球形成一个大致球形的耳石。正在经历修饰和聚集过程的小球体位于其中心部分，构成所谓的“核”。在受精后50小时，耳石是一个扁平的半球体。它由融合的小球组成，周围有两层同心层，其组织结构与成年鱼耳石中观察到的相似。在这个阶段，除了耳石的核之外，可以在耳石中检测到钙。我们认为，在新生耳石中发现的糖原分子可能允许诸如已知能固定钙的糖蛋白（胶原蛋白）等分子的插入。因此，糖原可能在启动耳石以及可能其他钙化组织的形成中起关键作用。
