Fulwiler C, Schmitt E A, Kim J M, Dowling J E
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
J Comp Neurol. 1997 May 19;381(4):449-60.
Determination of cell fate in the vertebrate retina has been shown to be largely independent of lineage. After cell fates are determined, retinal neurons become organized in a precise laminar pattern. The mechanisms for this patterning could involve morphogens distributed in gradients or, alternatively, direct cell-cell interactions. In the zebrafish mutant cyclops (Cyc(b16)), most embryos have two partial retinas joined in the ventral midline. This presents developing retinal cells near the midline with abnormal cellular environments, whereas laterally the pattern of developing cells is normal. We examined the consequences of this for patterning in the mutant's retina. We found that the retinas are joined in the midline at the apical surfaces of the photoreceptor layers. A laminar pattern emerges in the midline that preserves normal positional relationships between retinal cell types locally but is abnormal with respect to patterning over the entire retina. Lateral to the midline, retinal patterning appears normal. Metabolic labeling experiments showed that late rounds of DNA synthesis precede the emergence of the novel pattern in this midline region. We conclude that these observations in the cyclops mutant are compatible with mechanisms of pattern formation in the retina involving local cell interactions.
脊椎动物视网膜中细胞命运的确定在很大程度上被证明与细胞谱系无关。细胞命运确定后，视网膜神经元会以精确的分层模式进行组织。这种模式形成的机制可能涉及以梯度分布的形态发生素，或者直接的细胞间相互作用。在斑马鱼突变体独眼（Cyc(b16)）中，大多数胚胎有两个在腹侧中线相连的部分视网膜。这使得中线附近发育中的视网膜细胞处于异常的细胞环境中，而外侧发育中细胞的模式是正常的。我们研究了这种情况对突变体视网膜模式形成的影响。我们发现视网膜在光感受器层的顶端表面在中线处相连。在中线处出现了一种分层模式，该模式在局部保留了视网膜细胞类型之间的正常位置关系，但在整个视网膜的模式形成方面是异常的。在中线外侧，视网膜模式看起来正常。代谢标记实验表明，在这个中线区域，新一轮的DNA合成发生在新模式出现之前。我们得出结论，在独眼突变体中的这些观察结果与涉及局部细胞相互作用的视网膜模式形成机制是相符的。
