Glendining Kelly A, Liu Sam C, Nguyen Marvin, Dharmaratne Nuwan, Nagarajah Rajini, Iglesias Miguel A, Sawatari Atomu, Leamey Catherine A
Discipline of Physiology, School of Medical Sciences and Bosch Institute, F13, University of Sydney, Sydney, NSW, 2006, Australia.
BMC Neurosci. 2017 Dec 6;18(1):78. doi: 10.1186/s12868-017-0397-5.
The formation of visuotopically-aligned projections in the brain is required for the generation of functional binocular circuits. The mechanisms which underlie this process are unknown. Ten-m3 is expressed in a broad high-ventral to low-dorsal gradient across the retina and in topographically-corresponding gradients in primary visual centres. Deletion of Ten-m3 causes profound disruption of binocular visual alignment and function. Surprisingly, one of the most apparent neuroanatomical changes-dramatic mismapping of ipsilateral, but not contralateral, retinal axons along the representation of the nasotemporal retinal axis-does not correlate well with Ten-m3's expression pattern, raising questions regarding mechanism. The aim of this study was to further our understanding of the molecular interactions which enable the formation of functional binocular visual circuits.
Anterograde tracing, gene expression studies and protein pull-down experiments were performed. Statistical significance was tested using a Kolmogorov-Smirnov test, pairwise-fixed random reallocation tests and univariate ANOVAs.
We show that the ipsilateral retinal axons in Ten-m3 knockout mice are mismapped as a consequence of early axonal guidance defects. The aberrant invasion of the ventral-most region of the dorsal lateral geniculate nucleus by ipsilateral retinal axons in Ten-m3 knockouts suggested changes in the expression of other axonal guidance molecules, particularly members of the EphA-ephrinA family. We identified a consistent down-regulation of EphA7, but none of the other EphA-ephrinA genes tested, as well as an up-regulation of ipsilateral-determinants Zic2 and EphB1 in visual structures. We also found that Zic2 binds specifically to the intracellular domain of Ten-m3 in vitro.
Our findings suggest that Zic2, EphB1 and EphA7 molecules may work as effectors of Ten-m3 signalling, acting together to enable the wiring of functional binocular visual circuits.
大脑中视拓扑对齐投射的形成是功能性双眼视觉回路产生所必需的。这一过程背后的机制尚不清楚。Ten-m3在视网膜上从高腹侧到低背侧呈广泛梯度表达，在初级视觉中枢也呈拓扑对应梯度表达。Ten-m3的缺失会导致双眼视觉对齐和功能的严重破坏。令人惊讶的是，最明显的神经解剖学变化之一——同侧而非对侧视网膜轴突沿鼻颞视网膜轴代表区的显著错配——与Ten-m3的表达模式相关性不佳，这引发了关于机制的问题。本研究的目的是进一步了解促成功能性双眼视觉回路形成的分子相互作用。
进行了顺行示踪、基因表达研究和蛋白质下拉实验。使用Kolmogorov-Smirnov检验、成对固定随机重新分配检验和单因素方差分析来检验统计学显著性。
我们发现，Ten-m3基因敲除小鼠的同侧视网膜轴突因早期轴突导向缺陷而发生错配。Ten-m3基因敲除小鼠中同侧视网膜轴突对背侧外侧膝状核最腹侧区域的异常侵入表明其他轴突导向分子的表达发生了变化，特别是EphA-ephrinA家族的成员。我们发现EphA7持续下调，但其他测试的EphA-ephrinA基因均未下调，同时视觉结构中同侧决定因子Zic2和EphB1上调。我们还发现Zic2在体外能特异性结合Ten-m3的细胞内结构域。
我们的研究结果表明，Zic2、EphB1和EphA7分子可能作为Ten-m3信号的效应器共同发挥作用，促成功能性双眼视觉回路的布线。
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