Data from: Flightin maintains myofilament lattice organization required for optimal flight power and courtship song quality in Drosophila

The indirect flight muscles (IFMs) of Drosophila and other insects with asynchronous flight muscles are characterized by a crystalline myofilament lattice structure. The high-order lattice regularity is considered an adaptation for enhanced power output, but supporting evidence for this claim is lacking. We show that IFMs from transgenic flies expressing flightin with a deletion of its poorly conserved N-terminal domain (flnΔN62) have reduced inter-thick filament spacing and a less regular lattice. This resulted in a decrease in flight ability by 33% and in skinned fibre oscillatory power output by 57%, but had no effect on wingbeat frequency or frequency of maximum power output, suggesting that the underlying actomyosin kinetics is not affected and that the flight impairment arises from deficits in force transmission. Moreover, we show that flnΔN62 males produced an abnormal courtship song characterized by a higher sine song frequency and a pulse song with longer pulses and longer inter-pulse intervals (IPIs), the latter implicated in male reproductive success. When presented with a choice, wild-type females chose control males over mutant males in 92% of the competition events. These results demonstrate that flightin N-terminal domain is required for optimal myofilament lattice regularity and IFM activity, enabling powered flight and courtship song production. As the courtship song is subject to female choice, we propose that the low amino acid sequence conservation of the N-terminal domain reflects its role in fine-tuning species-specific courtship songs.

果蝇及其他拥有异步飞行肌的昆虫的间接飞行肌（indirect flight muscles, IFMs）以结晶状肌丝晶格结构为典型特征。学界普遍认为，这种高阶晶格规整性是提升功率输出的适应性演化特征，但目前仍缺乏支持该观点的实验证据。本研究发现，表达缺失保守性较弱的N端结构域的flightin（飞行蛋白）的转基因果蝇，其间接飞行肌的粗丝间距显著缩小，晶格规整性亦有所下降。该变化使得果蝇飞行能力降低33%，剥离表皮的肌纤维振荡功率输出下降57%，但对振翅频率或最大功率输出频率无显著影响，这提示肌动球蛋白动力学过程未受干扰，飞行能力受损源于力传递功能缺陷。此外，本研究还发现，携带flnΔN62突变的雄性果蝇会产生异常的求偶鸣曲：其正弦鸣曲频率更高，脉冲鸣曲的脉冲时长与脉冲间隔（inter-pulse intervals, IPIs）均更长——而脉冲间隔已被证实与雄性繁殖成功率密切相关。在择偶选择实验中，野生型（wild-type）雌性果蝇在92%的竞争选择事件中更倾向于选择野生型对照雄性，而非突变体雄性。上述实验结果证实，flightin的N端结构域是维持最优肌丝晶格规整性与间接飞行肌功能的必需元件，保障了动力飞行与求偶鸣曲的正常进行。鉴于求偶鸣曲受雌性择偶选择的调控，我们推测flightin N端结构域较低的氨基酸序列保守性，与其在微调物种特异性求偶鸣曲中的功能息息相关。