Sequential Retraction Segregates SGN Processes during Target Selection in the Cochlea
Sequential Retraction Segregates SGN Processes during Target Selection in the Cochlea
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DOI：
10.1523/jneurosci.2236-15.2015
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发表时间：
2015-12-09
影响因子：
5.3
通讯作者：
Goodrich, Lisa V.
中科院分区：
文献类型：
--
作者：
Druckenbrod, Noah R.;Goodrich, Lisa V.
神经系统的一个标志是不同类型的神经元之间存在精确的连接模式。许多机制可以用来建立特异性，包括嗜同性粘附和突触细化，但在整个神经系统中使用的策略范围仍然不清楚。为了拓宽神经元如何找到它们的目标的理解，我们研究了发育中的小鼠耳蜗，其中两类螺旋神经节神经元（SGN），I型和II型，一起导航到感觉上皮，然后分别分开接触内毛细胞（IHC）或外毛细胞（OHC）。具有I型和II型形态的神经元在出生前就很明显，这表明目标选择可能通过从OHC区域排除I型过程来完成。然而，由于I型过程似乎过冲进入II型领土出生后，特异性也可能取决于消除不适当的突触。为了解决这些差异，我们分析了单个纤维及其分支与潜在伙伴相互作用时的形态和动态行为。我们发现，SGN过程继续隔离解剖出生后的耳蜗。虽然I型样纤维在局部分支，但很少有分支接触外毛细胞，这与突触消除有关。相反，时间推移成像研究表明，一个突出的作用，收回，首先定位过程中的适当区域，然后在随后的一段时期内，旺盛的增长和完善的分支。因此，收缩的连续阶段可以帮助实现目标特异性，增加可用于塑造神经回路的机制列表。
A hallmark of the nervous system is the presence of precise patterns of connections between different types of neurons. Many mechanisms can be used to establish specificity, including homophilic adhesion and synaptic refinement, but the range of strategies used across the nervous system remains unclear. To broaden the understanding of how neurons find their targets, we studied the developing murine cochlea, where two classes of spiral ganglion neurons (SGNs), type I and type II, navigate together to the sensory epithelium and then diverge to contact inner hair cells (IHCs) or outer hair cells (OHCs), respectively. Neurons with type I and type II morphologies are apparent before birth, suggesting that target selection might be accomplished by excluding type I processes from the OHC region. However, because type I processes appear to overshoot into type II territory postnatally, specificity may also depend on elimination of inappropriate synapses. To resolve these differences, we analyzed the morphology and dynamic behaviors of individual fibers and their branches as they interact with potential partners. We found that SGN processes continue to be segregated anatomically in the postnatal cochlea. Although type I-like fibers branched locally, few branches contacted OHCs, arguing against synaptic elimination. Instead, time-lapse imaging studies suggest a prominent role for retraction, first positioning processes to the appropriate region and then corralling branches during a subsequent period of exuberant growth and refinement. Thus, sequential stages of retraction can help to achieve target specificity, adding to the list of mechanisms available for sculpting neural circuits.