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首页> 外文期刊>Development >Drosophila N-cadherin functions in the first stage of the two-stage layer-selection process of R7 photoreceptor afferents.
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Drosophila N-cadherin functions in the first stage of the two-stage layer-selection process of R7 photoreceptor afferents.

机译：果蝇N-钙黏着蛋白在R7感光受体的两阶段层选择过程的第一阶段起作用。

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摘要

Visual information received from the three types of photoreceptor neurons (R1-R6, R7 and R8) in the fly compound eyes converges to the external part of the medulla neuropil (M1-M6 layers) in a layer-specific fashion: R7 and R8 axons terminate at the M6 and M3 layers, respectively, whereas lamina neurons (L1-L5) relay R1-R6 to multiple medulla layers (M1-M5). Here, we show that during development, R7 and R8 neurons establish layer-specific projections in two separate stages: during the first stage, R7 and R8 axons sequentially target to the R7- and R8-temporary layers, respectively; and at the second stage, R7 and R8 growth cones progress synchronously to their destined layers. Using a set of mutations that delete different afferent subsets or alter R7 connectivity, we defined the mechanism of layer selection. We observed that R8, R7 and L1-L5 afferents target to their temporary layers independently, suggesting that afferent-target, but not afferent-afferent, interactions dictate the targeting specificity. N-cadherin is required in the first stage for R7 growth cones to reach and remain in the R7-temporary layer. The Ncad gene contains three pairs of alternatively spliced exons and encodes 12 isoforms. However, expressing a single Ncad isoform in Ncad mutant R7s is sufficient to rescue mistargeting phenotypes. Furthermore, Ncad isoforms mediate promiscuous heterophilic interactions in an in vitro cell-aggregation assay. We propose that Ncad isoforms do not form an adhesion code; rather, they provide permissive adhesion between R7 growth cones and their temporary targets.
机译：在复眼中从三种类型的感光神经元（R1-R6，R7和R8）接收到的视觉信息以特定于层的方式会聚到髓质神经丛（M1-M6层）的外部：R7和R8轴突。分别在M6和M3层终止，而层神经元（L1-L5）将R1-R6中继到多个延髓层（M1-M5）。在这里，我们显示了在发育过程中，R7和R8神经元在两个单独的阶段建立了特定于层的投影：在第一阶段，R7和R8轴突分别依次靶向R7和R8临时层;在第二阶段，R7和R8生长锥同步到达其预定层。使用一组删除不同传入子集或更改R7连接性的突变，我们定义了层选择的机制。我们观察到R8，R7和L1-L5传入分子独立地靶向其临时层，这表明传入靶标而不是传入传入相互作用决定了靶向特异性。在第一阶段，需要N-钙粘着蛋白才能使R7生长锥到达并保留在R7临时层中。 Ncad基因包含三对交替剪接的外显子，并编码12个同工型。但是，在Ncad突变体R7s中表达单个Ncad异构体足以挽救错误定位的表型。此外，在体外细胞聚集试验中，Ncad同工型介导混杂的异种相互作用。我们建议Ncad同工型不形成粘附代码。相反，它们在R7生长锥与其临时目标之间提供了允许的附着力。

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