Laboratory of Cell Recognition and Pattern Formation, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, Japan.
Neural Dev. 2009 Oct 2;4:37. doi: 10.1186/1749-8104-4-37.
For the establishment of functional neural circuits that support a wide range of animal behaviors, initial circuits formed in early development have to be reorganized. One way to achieve this is local remodeling of the circuitry hardwiring. To genetically investigate the underlying mechanisms of this remodeling, one model system employs a major group of Drosophila multidendritic sensory neurons - the dendritic arborization (da) neurons - which exhibit dramatic dendritic pruning and subsequent growth during metamorphosis. The 15 da neurons are identified in each larval abdominal hemisegment and are classified into four categories - classes I to IV - in order of increasing size of their receptive fields and/or arbor complexity at the mature larval stage. Our knowledge regarding the anatomy and developmental basis of adult da neurons is still fragmentary.
We identified multidendritic neurons in the adult Drosophila abdomen, visualized the dendritic arbors of the individual neurons, and traced the origins of those cells back to the larval stage. There were six da neurons in abdominal hemisegment 3 or 4 (A3/4) of the pharate adult and the adult just after eclosion, five of which were persistent larval da neurons. We quantitatively analyzed dendritic arbors of three of the six adult neurons and examined expression in the pharate adult of key transcription factors that result in the larval class-selective dendritic morphologies. The 'baseline design' of A3/4 in the adult was further modified in a segment-dependent and age-dependent manner. One of our notable findings is that a larval class I neuron, ddaE, completed dendritic remodeling in A2 to A4 and then underwent caspase-dependent cell death within 1 week after eclosion, while homologous neurons in A5 and in more posterior segments degenerated at pupal stages. Another finding is that the dendritic arbor of a class IV neuron, v'ada, was immediately reshaped during post-eclosion growth. It exhibited prominent radial-to-lattice transformation in 1-day-old adults, and the resultant lattice-shaped arbor persisted throughout adult life.
Our study provides the basis on which we can investigate the genetic programs controlling dendritic remodeling and programmed cell death of adult neurons, and the life-long maintenance of dendritic arbors.
为了建立支持广泛动物行为的功能性神经回路，最初在早期发育中形成的回路必须进行重组。实现这一目标的一种方法是对电路的硬连线进行局部重塑。为了从遗传学上研究这种重塑的潜在机制，一个模型系统采用了果蝇多树突状感觉神经元的一个主要群体 - 树突分枝（da）神经元 - 在变态期间表现出明显的树突修剪和随后的生长。在每个幼虫腹部半节段中鉴定出 15 个 da 神经元，并按其感受野的大小和/或成熟幼虫阶段树突复杂性的顺序分为四类 - I 到 IV 类。我们对成年 da 神经元的解剖结构和发育基础的了解仍然很零碎。
我们在成年果蝇腹部鉴定出多树突神经元，可视化了单个神经元的树突分支，并追溯到这些细胞的起源回到幼虫阶段。在成虫刚羽化后的幼虫 3 或 4 个半节段（A3/4）或成虫中存在 6 个 da 神经元，其中 5 个是持续存在的幼虫 da 神经元。我们对 6 个成年神经元中的 3 个进行了定量分析，并检查了关键转录因子在成虫中表达的情况，这些转录因子导致了幼虫的类选择性树突形态。成虫 A3/4 的“基线设计”以节段依赖性和年龄依赖性的方式进一步修改。我们的一个显著发现是，一个幼虫 I 类神经元，ddaE，在 A2 到 A4 完成了树突重塑，然后在羽化后 1 周内经历了 Caspase 依赖性细胞死亡，而 A5 中的同源神经元和更后段的神经元在蛹期退化。另一个发现是，IV 类神经元 v'ada 的树突分支在羽化后生长过程中立即重塑。它在 1 日龄成虫中表现出明显的从放射状到格子状的转变，并且所得的格子状树突在成虫的整个生命周期中都保持不变。
我们的研究为我们研究控制成年神经元树突重塑和程序性细胞死亡的遗传程序以及树突分支的终生维持提供了基础。
