Hogan D, Williams R W
Department of Anatomy and Neurobiology, School of Medicine, University of Tennessee, Memphis 38163.
J Comp Neurol. 1995 Feb 13;352(3):367-80. doi: 10.1002/cne.903520305.
An autosomal recessive mutation carried in a family of black Belgian sheepdogs eliminates the optic chiasm--all retinal ganglion cell axons extend directly into the ipsilateral optic tract. One key issue we are trying to resolve is whether the retina or the chiasm is the principal site of mutant gene action. In this study, we have examined retinas of mutants to discover any associated changes in retinal structure. Retinas of mutant animals are relatively normal. Inner and outer nuclear layers are qualitatively indistinguishable from those of normal dogs. The principal difference is that the area centralis of mutants is smaller and had a lower peak ganglion cell density than that of normal dogs (8,100 vs 10,500/mm2, P < 0.05). This mutant phenotype is similar to that seen in retinas of Siamese cats and albino ferrets. Beyond area centralis, the central-to-peripheral gradient in ganglion cell density is normal in mutants. The size of the optic nerves, density of axons, and total number of axons do not differ between mutant and normal dogs. One of three mutant dogs had a small abnormal optic chiasm. Retrograde labeling of ganglion cells demonstrated that the residual crossed projection originated from cells in a widespread region in nasal retina and not solely from the peripheral nasal region, as might be expected of an anti-albino. Although our analysis does not rule out the retina as a site of mutant gene action, the modest differences between mutant and normal retinas suggest that the mutation either acts outside the retina or exerts a highly specific effect on ganglion cell trajectories alone.
在一个黑色比利时牧羊犬家族中携带的常染色体隐性突变导致视交叉缺失——所有视网膜神经节细胞轴突直接延伸至同侧视束。我们试图解决的一个关键问题是，突变基因作用的主要位点是视网膜还是视交叉。在本研究中，我们检查了突变体的视网膜，以发现视网膜结构中的任何相关变化。突变动物的视网膜相对正常。内核层和外核层在质量上与正常犬的无法区分。主要区别在于，突变体的中央凹面积较小，神经节细胞密度峰值低于正常犬（8100个/mm² 对10500个/mm²，P < 0.05）。这种突变表型与暹罗猫和白化雪貂视网膜中的表型相似。在中央凹之外，突变体神经节细胞密度的中央到周边梯度是正常的。突变犬和正常犬的视神经大小、轴突密度和轴突总数没有差异。三只突变犬中有一只的视交叉有小的异常。神经节细胞的逆行标记表明，残余的交叉投射起源于鼻侧视网膜广泛区域的细胞，而不仅仅是预期的抗白化病动物的周边鼻侧区域。虽然我们的分析不排除视网膜是突变基因作用的位点，但突变体和正常视网膜之间的适度差异表明，该突变要么在视网膜外起作用，要么仅对神经节细胞轨迹产生高度特异性影响。
