Stubbs J, Palmer A, Vidovic M, Marotte L R
Developmental Neurobiology and Endocrinology Group, Research School of Biological Sciences, Australian National University, Canberra, ACT 0200, Australia.
Eur J Neurosci. 2000 Oct;12(10):3626-36. doi: 10.1046/j.1460-9568.2000.00251.x.
We describe the expression of EphA3 and EphA7 receptors and ephrin-A2 ligand in the retina and the superior colliculus during the development of the retinocollicular projection in the marsupial wallaby (Macropus eugenii), using immunoblotting and immunohistochemistry. EphA3 in the retina was in a striking, low central to high peripheral gradient, superimposed on which was a high temporal to low nasal level of expression. This distribution was evident from postnatal day 30, when axons are growing into the colliculus and forming a coarsely organized topographic projection, to postnatal day 65, when axons have arborized in their correct retinotopic positions. EphA7 showed a shallow centroperipheral gradient with no nasotemporal differences in expression. In the superior colliculus no rostrocaudal differences in distribution were detected for either of these receptors. Ephrin-A2 was distributed in a gradient increasing from the rostral to the caudal pole in the superficial layers of the superior colliculus only up to postnatal day 30. Ephrin-A2 was evenly distributed in the retina throughout development of the projection. Expression of EphA3 in the retina increased, while the expression of ephrin-A2 in the colliculus was downregulated over time. The graded expression of EphA3 and ephrin-A2 early in the development of the projection suggests that they play a role in establishment of coarse topography of retinal axons along the rostrocaudal axis of the superior colliculus. However, the gradients were not complementary, meaning that EphA3 alone cannot mediate the repulsive interactions with ephrin-A2 that have been postulated to underlie formation of the topographic map.
我们运用免疫印迹法和免疫组织化学法，描述了有袋类动物沙袋鼠（袋獾）视网膜-上丘投射发育过程中EphA3和EphA7受体以及ephrin-A2配体在视网膜和上丘中的表达情况。视网膜中的EphA3呈现出显著的从中央低水平到周边高水平的梯度分布，在此基础上叠加了从颞侧高水平到鼻侧低水平的表达。这种分布在出生后第30天就很明显，此时轴突正长入上丘并形成粗略组织的地形图，到出生后第65天，轴突已在其正确的视网膜定位位置分支。EphA7显示出从中央到周边的浅梯度，在表达上没有鼻颞差异。在上丘中，未检测到这两种受体在前后分布上的差异。Ephrin-A2仅在出生后第30天之前，在上丘表层从吻端到尾端呈现出梯度增加的分布。在投射的整个发育过程中，Ephrin-A2在视网膜中均匀分布。随着时间的推移，视网膜中EphA3的表达增加，而上丘中ephrin-A2的表达下调。投射发育早期EphA3和ephrin-A2的梯度表达表明它们在沿着上丘前后轴建立视网膜轴突的粗略地形图中发挥作用。然而，这些梯度并不互补，这意味着仅EphA3不能介导与ephrin-A2的排斥性相互作用，而这种相互作用被认为是地形图形成的基础。
