Wheeler D A, Hamblen-Coyle M J, Dushay M S, Hall J C
Department of Biology, Brandeis University, Waltham, Massachusetts 02254.
J Biol Rhythms. 1993 Spring;8(1):67-94. doi: 10.1177/074873049300800106.
Certain of the rhythm mutations in Drosophila melanogaster lead to arrhythmic locomotor activity (and aperiodic eclosion) in constant conditions. In light-dark (LD) cycles, however, such mutants exhibit clear fluctuations between high levels of activity when the lights are on and much lower ones when they are off. Our data, in contrast to some previous conclusions, strongly suggest that period0 (per0) adults are, in LD conditions, merely being "forced" into exhibiting periodic behavior. These experiments involved application of 8-, 12-, 16-, and 24-hr LD cycles, in which the arrhythmic mutant could have any of these periodicities imposed upon it, whereas wild-type flies tended to exhibit periods of about 24 hr in cycling conditions whose T values were > 8 hr different from 24. In phase-shift experiments, it was found that Drosophila expressing genotypes associated with rhythmicity achieved a 5-hr advance over a 2-day period following an advanced lights-on; per0 adults altered the phase of their locomotor peaks more rapidly. Against a background of the fact that eyeless or blind flies exhibit normal entrainment, it was hypothesized that double-mutant flies--carrying such visual mutations and per0 as well--should not synchronize to LD cycles, if the forced rhythms seen in the latter single-mutant type are mediated solely by light input through the external photoreceptors. Since an appreciable proportion of the double mutants did synchronize (to LD 12:12), it is thus suggested that the visual cues involved in forcing rhythmicity could be input through the same extraocular photoreceptors that, in general, subserve the fly's rhythm system.
黑腹果蝇中的某些节律突变在恒定条件下会导致无节律的运动活动（以及非周期性羽化）。然而，在明暗（LD）循环中，此类突变体在光照时表现出高水平的活动，而在黑暗时则表现出低得多的活动，呈现出明显的波动。与之前的一些结论相反，我们的数据强烈表明，在LD条件下，period0（per0）成虫仅仅是被“强迫”表现出周期性行为。这些实验涉及应用8小时、12小时、16小时和24小时的LD循环，在此条件下，无节律的突变体可能会被强加这些周期性中的任何一种，而野生型果蝇在T值与24小时相差>8小时的循环条件下往往表现出约24小时的周期。在相移实验中发现，表达与节律性相关基因型的果蝇在提前开灯后的两天内提前了5小时；per0成虫更快地改变了其运动高峰的相位。鉴于无眼或失明的果蝇表现出正常的同步这一事实，有人推测，如果在后者单突变类型中看到的强迫节律仅由通过外部光感受器的光输入介导，那么携带此类视觉突变和per0的双突变果蝇不应与LD循环同步。由于相当一部分双突变体确实同步了（到LD 12:12），因此表明，参与强迫节律性的视觉线索可能通过通常为果蝇节律系统服务的相同眼外光感受器输入。
