Fachbereich Biowissenschaften der J.W. Goethe-Universität Frankfurt, Frankfurt am Main, Germany.
PLoS One. 2011;6(5):e20091. doi: 10.1371/journal.pone.0020091. Epub 2011 May 25.
The Radical-Pair-Model postulates that the reception of magnetic compass directions in birds is based on spin-chemical reactions in specialized photopigments in the eye, with cryptochromes discussed as candidate molecules. But so far, the exact subcellular characterization of these molecules in the retina remained unknown.
METHODOLOGY/PRINCIPAL FINDINGS: We here describe the localization of cryptochrome 1a (Cry1a) in the retina of European robins, Erithacus rubecula, and domestic chickens, Gallus gallus, two species that have been shown to use the magnetic field for compass orientation. In both species, Cry1a is present exclusively in the ultraviolet/violet (UV/V) cones that are distributed across the entire retina. Electron microscopy shows Cry1a in ordered bands along the membrane discs of the outer segment, and cell fractionation reveals Cry1a in the membrane fraction, suggesting the possibility that Cry1a is anchored along membranes.
CONCLUSIONS/SIGNIFICANCE: We provide first structural evidence that Cry1a occurs within a sensory structure arranged in a way that fulfils essential requirements of the Radical-Pair-Model. Our findings, identifying the UV/V-cones as probable magnetoreceptors, support the assumption that Cry1a is indeed the receptor molecule mediating information on magnetic directions, and thus provide the Radical-Pair-Model with a profound histological background.
自由基对模型假定鸟类对磁场方向的感知是基于眼睛中专门的光色素中的自旋化学反应，而隐花色素被认为是候选分子。但到目前为止，这些分子在视网膜中的确切亚细胞特征仍然未知。
方法/主要发现：我们在这里描述了欧洲知更鸟（Erithacus rubecula）和家鸡（Gallus gallus）视网膜中隐花色素 1a（Cry1a）的定位，这两种物种都被证明可以利用磁场进行罗盘定位。在这两个物种中，Cry1a 仅存在于分布在整个视网膜上的紫外线/紫光（UV/V）锥体中。电子显微镜显示 Cry1a 沿外节膜盘排列成有序的带，细胞分级分离显示 Cry1a 存在于膜部分，这表明 Cry1a 可能沿着膜锚定。
结论/意义：我们提供了第一个结构证据，证明 Cry1a 存在于一种以满足自由基对模型基本要求的方式排列的感觉结构中。我们的发现将 UV/V-锥体确定为可能的磁感受器，支持了 Cry1a 确实是介导磁场方向信息的受体分子的假设，从而为自由基对模型提供了深刻的组织学背景。
