Dahm Ralf, Schonthaler Helia B, Soehn Anne S, van Marle Jan, Vrensen Gijs F J M
Max-Planck-Institute for Developmental Biology, Spemannstrasse 35, D-72076 Tübingen, Germany.
Exp Eye Res. 2007 Jul;85(1):74-89. doi: 10.1016/j.exer.2007.02.015. Epub 2007 Mar 19.
The zebrafish has become an important vertebrate model organism to study the development of the visual system. Mutagenesis projects have resulted in the identification of hundreds of eye mutants. Analysis of the phenotypes of these mutants relies on in depth knowledge of the embryogenesis in wild-type animals. While the morphological events leading to the formation of the retina and its connections to the central nervous system have been described in great detail, the characterization of the development of the eye lens is still incomplete. In the present study, we provide a morphological description of embryonic and larval lens development as well as adult lens morphology in the zebrafish. Our analyses show that, in contrast to other vertebrate species, the zebrafish lens delaminates from the surface ectoderm as a solid cluster of cells. Detachment of the prospective lens from the surface ectoderm is facilitated by apoptosis. Primary fibre cell elongation occurs in a circular fashion resulting in an embryonic lens nucleus with concentric shells of fibres. After formation of a monolayer of lens epithelial cells, differentiation and elongation of secondary lens fibres result in a final lens morphology similar to that of other vertebrate species. As in other vertebrates, secondary fibre cell differentiation includes the programmed degradation of nuclei, the interconnection of adjacent fibres via protrusions at the fibre cells' edges and the establishment of gap junctions between lens fibre cells. The very close spacing of the nuclei of the differentiating secondary fibres in a narrow zone close to the equatorial epithelium, however, suggests that secondary fibre cell differentiation deviates from that described for mammalian or avian lenses. In summary, while there are similarities in the development and final morphology of the zebrafish lens with mammalian and avian lenses, there are also significant differences, suggesting caution when extrapolating findings on the zebrafish to, for example, human lens development or function.
斑马鱼已成为研究视觉系统发育的重要脊椎动物模式生物。诱变项目已鉴定出数百种眼睛突变体。对这些突变体表型的分析依赖于对野生型动物胚胎发生的深入了解。虽然导致视网膜形成及其与中枢神经系统连接的形态学事件已被详细描述，但晶状体发育的特征仍不完整。在本研究中，我们提供了斑马鱼胚胎和幼体晶状体发育以及成体晶状体形态的形态学描述。我们的分析表明，与其他脊椎动物物种不同，斑马鱼晶状体作为一个实心细胞簇从表面外胚层分层。凋亡促进了预期晶状体与表面外胚层的分离。初级纤维细胞以圆形方式伸长，形成一个具有同心纤维壳的胚胎晶状体核。在形成单层晶状体上皮细胞后，次级晶状体纤维的分化和伸长导致最终的晶状体形态与其他脊椎动物物种相似。与其他脊椎动物一样，次级纤维细胞分化包括细胞核的程序性降解、相邻纤维通过纤维细胞边缘的突起相互连接以及晶状体纤维细胞之间间隙连接的建立。然而，在靠近赤道上皮的狭窄区域中，分化的次级纤维细胞核的紧密间距表明次级纤维细胞分化与哺乳动物或鸟类晶状体的情况有所不同。总之，虽然斑马鱼晶状体的发育和最终形态与哺乳动物和鸟类晶状体有相似之处，但也存在显著差异，这表明在将斑马鱼的研究结果外推至例如人类晶状体发育或功能时应谨慎。
