Weber Paweł, Kula-Eversole Elzbieta, Pyza Elzbieta
Department of Cytology and Histology, Institute of Zoology, Jagiellonian University, Kraków, Poland.
PLoS One. 2009;4(1):e4290. doi: 10.1371/journal.pone.0004290. Epub 2009 Jan 28.
In the first optic neuropil (lamina) of the fly's visual system, monopolar cells L1 and L2 and glia show circadian rhythms in morphological plasticity. They change their size and shape during the day and night. The most pronounced changes have been detected in circadian size of the L2 axons. Looking for a functional significance of the circadian plasticity observed in axons, we examined the morphological plasticity of the L2 dendrites. They extend from axons and harbor postsynaptic sites of tetrad synaptic contacts from the photoreceptor terminals.
METHODOLOGY/PRINCIPAL FINDINGS: The plasticity of L2 dendrites was evaluated by measuring an outline of the L2 dendritic trees. These were from confocal images of cross sections of L2 cells labeled with GFP. They were in wild-type and clock mutant flies held under different light conditions and sacrified at different time points. We found that the L2 dendrites are longest at the beginning of the day in both males and females. This rhythm observed under a day/night regime (LD) was maintained in constant darkness (DD) but not in continuous light (LL). This rhythm was not present in the arrhythmic per(01) mutant in LD or in DD. In the clock photoreceptor cry(b) mutant the rhythm was maintained but its pattern was different than that observed in wild-type flies.
CONCLUSIONS/SIGNIFICANCE: The results obtained showed that the L2 dendrites exhibit circadian structural plasticity. Their morphology is controlled by the per gene-dependent circadian clock. The L2 dendrites are longest at the beginning of the day when the daytime tetrad presynaptic sites are most numerous and L2 axons are swollen. The presence of the rhythm, but with a different pattern in cry(b) mutants in LD and DD indicates a new role of cry in the visual system. The new role is in maintaining the circadian pattern of changes of the L2 dendrite length and shape.
在果蝇视觉系统的第一个视神经纤维层（神经层）中，单极细胞L1和L2以及神经胶质细胞在形态可塑性方面表现出昼夜节律。它们在白天和夜晚会改变大小和形状。在L2轴突的昼夜大小变化中检测到最明显的改变。为了探寻轴突中观察到的昼夜可塑性的功能意义，我们研究了L2树突的形态可塑性。L2树突从轴突延伸出来，并含有来自光感受器终端的四联突触接触的突触后位点。
方法/主要发现：通过测量L2树突树的轮廓来评估L2树突的可塑性。这些轮廓来自用绿色荧光蛋白（GFP）标记的L2细胞横截面的共聚焦图像。实验对象是野生型和生物钟突变型果蝇，它们处于不同光照条件下，并在不同时间点处死。我们发现，无论雄性还是雌性，L2树突在一天开始时最长。在昼夜交替（LD）条件下观察到的这种节律在持续黑暗（DD）中得以维持，但在持续光照（LL）中则不然。在LD或DD条件下，无节律的per(01)突变体中不存在这种节律。在生物钟光感受器cry(b)突变体中，该节律得以维持，但其模式与野生型果蝇中观察到的不同。
结论/意义：所得结果表明，L2树突表现出昼夜结构可塑性。它们的形态受per基因依赖的生物钟控制。当白天的四联突触前位点最多且L2轴突肿胀时，L2树突在一天开始时最长。在LD和DD条件下，cry(b)突变体中存在该节律，但模式不同，这表明cry在视觉系统中有新作用。新作用是维持L2树突长度和形状变化的昼夜模式。
