Shin Sae Kyung, O'Brien Keely M Bumsted
Optometry and Vision Science, The University of Auckland, Auckland, NZ.
BMC Dev Biol. 2009 Nov 25;9:57. doi: 10.1186/1471-213X-9-57.
Nervous system development is dependent on early regional specification to create functionally distinct tissues within an initially undifferentiated zone. Within the retina, photoreceptors are topographically organized with rod free area centrales faithfully generated at the centre of gaze. How does the developing eye regulate this placement? Conventional wisdom indicates that the distal tip of the growing optic vesicle (OV) gives rise to the area centralis/fovea. Ectopic expression and ablation studies do not fully support this view, creating a controversy as to the origin of this region. In this study, the lineage of cells in the chicken OV was traced using DiI. The location of labelled cells was mapped onto the retina in relation to the rod-free zone at embryonic (E) 7 and E17.5. The ability to regenerate a rod free area after OV ablation was determined in conjunction with lineage tracing.
Anterior OV gave rise to cells in nasal retina and posterior OV became temporal retina. The OV distal tip gave rise to cells above the optic nerve head. A dorsal and anterior region of the OV correlated with cells in the developing rod free area centralis. Only ablations including the dorsal anterior region gave rise to a retina lacking a rod free zone. DiI application after ablation indicated that cells movements were greater along the anterior/posterior axis compared with the dorsal/ventral axis.
Our data support the idea that the chicken rod free area centralis originates from cells located near, but not at the distal tip of the developing OV. Therefore, the hypothesis that the area centralis is derived from cells at the distal tip of the OV is not supported; rather, a region anterior and dorsal to the distal tip gives rise to the rod free region. When compared with other studies of retinal development, our results are supported on molecular, morphological and functional levels. Our data will lead to a better understanding of the mechanisms underlying the topographic organization of the retina, the origin of the rod free zone, and the general issue of compartmentalization of neural tissue before any indication of morphological differentiation.
神经系统的发育依赖于早期区域特化，以便在最初未分化的区域内形成功能不同的组织。在视网膜中，光感受器呈拓扑排列，无杆区中央在注视中心忠实地形成。发育中的眼睛如何调节这种位置？传统观点认为，不断生长的视泡（OV）的远端尖端产生中央区/中央凹。异位表达和消融研究并不完全支持这一观点，引发了关于该区域起源的争议。在本研究中，使用DiI追踪鸡OV中细胞的谱系。将标记细胞的位置相对于胚胎（E）7和E17.5时的无杆区映射到视网膜上。结合谱系追踪确定OV消融后再生无杆区的能力。
前OV产生鼻侧视网膜中的细胞，后OV变成颞侧视网膜。OV远端尖端产生视神经乳头上方的细胞。OV的背侧和前部区域与发育中的无杆区中央的细胞相关。只有包括背侧前部区域的消融导致缺乏无杆区的视网膜。消融后应用DiI表明，细胞沿前后轴的移动比背腹轴更大。
我们的数据支持这样的观点，即鸡的无杆区中央起源于发育中的OV附近但不是远端尖端的细胞。因此，中央区源自OV远端尖端细胞的假设不成立；相反，远端尖端前方和背侧的区域产生无杆区。与其他视网膜发育研究相比，我们的结果在分子、形态和功能水平上得到了支持。我们的数据将有助于更好地理解视网膜拓扑组织、无杆区起源以及神经组织在出现任何形态分化迹象之前的分隔化这一普遍问题的潜在机制。
