Yale School of Public Health, Yale University, New Haven, CT 06520, USA.
Insect Biochem Mol Biol. 2012 May;42(5):360-70. doi: 10.1016/j.ibmb.2012.01.007.
Female tsetse flies undergo viviparous reproduction, generating one larva each gonotrophic cycle. Larval nourishment is provided by the mother in the form of milk secretions. The milk consists mostly of lipids during early larval development and shifts to a balanced combination of protein and lipids in the late larval instars. Provisioning of adequate lipids to the accessory gland is an indispensable process for tsetse fecundity. This work investigates the roles of Brummer lipase (Bmm) and the adipokinetic hormone (AKH)/adipokinetic hormone receptor (AKHR) systems on lipid metabolism and mobilization during lactation in tsetse. The contributions of each system were investigated by a knockdown approach utilizing siRNA injections. Starvation experiments revealed that silencing of either system results in prolonged female lifespan. Simultaneous suppression of bmm and akhr prolonged survival further than either individual knockdown. Knockdown of akhr and bmm transcript levels resulted in high levels of whole body lipids at death, indicating an inability to utilize lipid reserves during starvation. Silencing of bmm resulted in delayed oocyte development. Respective reductions in fecundity of 20 and 50% were observed upon knockdown of akhr and bmm, while simultaneous knockdown of both genes resulted in 80% reduction of larval production. Omission of one bloodmeal during larvigenesis (nutritional stress) after simultaneous knockdown led to almost complete suppression of larval production. This phenotype likely results from tsetse's inability to utilize lipid reserves as loss of both lipolysis systems leads to accumulation and retention of stored lipids during pregnancy. This shows that both Bmm lipolysis and AKH/AKHR signaling are critical for lipolysis required for milk production during tsetse pregnancy, and identifies the underlying mechanisms of lipid metabolism critical to tsetse lactation. The similarities in the lipid metabolic pathways and other aspects of milk production between tsetse and mammals indicate that this fly could be used as a novel model for lactation research.
雌性采采蝇通过胎生繁殖，每个生殖周期产生一只幼虫。幼虫的营养由母亲以乳汁分泌的形式提供。在幼虫早期发育阶段，乳汁主要由脂质组成，而在后期幼虫龄期则转变为蛋白质和脂质的平衡组合。为附腺提供足够的脂质是采采蝇繁殖力所必需的过程。这项工作研究了 Brummer 脂肪酶 (Bmm) 和促肾上腺皮质激素 (AKH)/促肾上腺皮质激素受体 (AKHR) 系统在采采蝇泌乳期间对脂质代谢和动员的作用。通过利用 siRNA 注射进行敲低方法研究了每个系统的贡献。饥饿实验表明，敲低任一系统都会延长雌性寿命。同时抑制 bmm 和 akhr 的生存时间进一步超过了任何一个单独的敲低。敲低 bmm 和 akhr 的转录水平导致死亡时全身脂质水平升高，表明在饥饿期间无法利用脂质储备。沉默 bmm 导致卵母细胞发育延迟。在敲低 akhr 和 bmm 时，观察到生育力分别降低 20%和 50%，而同时敲低这两个基因导致幼虫产量降低 80%。在同时敲低后幼虫发生期间（营养胁迫）省略一次血餐导致幼虫产量几乎完全抑制。这种表型可能是由于采采蝇无法利用脂质储备，因为两个脂肪分解系统的丧失导致在怀孕期间储存的脂质积累和保留。这表明 Bmm 脂肪分解和 AKH/AKHR 信号传导对于采采蝇怀孕期间乳汁产生所需的脂肪分解都是至关重要的，并确定了与采采蝇泌乳至关重要的脂质代谢的潜在机制。采采蝇和哺乳动物之间在脂质代谢途径和其他乳汁生产方面的相似性表明，这种苍蝇可以用作泌乳研究的新型模型。
