Institut de Biologia Integrativa de Sistemes, Parc Cientific Universitat de València, C/ Catedrático José Beltrán nº 2, 46980, Paterna, València, Spain.
Institut de Biologia Integrativa de Sistemes, Parc Cientific Universitat de València, C/ Catedrático José Beltrán nº 2, 46980, Paterna, València, Spain.
Insect Biochem Mol Biol. 2019 Sep;112:103185. doi: 10.1016/j.ibmb.2019.103185. Epub 2019 Jul 7.
Aphids were the first animals reported as photoperiodic as their life cycles are strongly determined by the photoperiod. During the favourable seasons (characterised by long days) aphid populations consist exclusively of viviparous parthenogenetic females (known as virginoparae). Shortening of the photoperiod in autumn is perceived by aphids as the signal that anticipates the harsh season, leading to a switch in the reproductive mode giving place to the sexual morphs (oviparae females and males) that mate and lay winter-resistant (diapause-like) eggs. The molecular and cellular basis governing the switch between the two reproductive modes are far from being understood. Classical experiments identified a group of neurosecretory cells in the pars intercerebralis of the aphid brain (the so called group I of neurosecretory cells) that were essential for the development of embryos as parthenogenetic females and were thus proposed to synthesise a parthenogenesis promoting substance that was termed "virginoparin". Since insulin-like peptides (ILPs) have been implicated in the control of diapause in other insects, we investigated their involvement in aphid photoperiodism. We compared the expression of two ILPs (ILP1 and ILP4) and an Insulin receptor coding genes in A. pisum aphids reared under long- and short-day conditions. The three genes showed higher expression in long-day reared aphids. In addition, we localised the site of expression of the two ILP genes in the aphid brain. Both genes were found to be expressed in the group I of neurosecretory cells. Altogether, our results suggest that ILP1 and ILP4 play an important role in the control of the aphid life-cycle by promoting the parthenogenetic development during long-day seasons while their repression by short days would activate the sexual development. Thus we propose these ILPs correspond to the so called "virginoparin" by early bibliography. A possible connection with the circadian system is also discussed.
蚜虫是最早被报道具有光周期现象的动物，因为它们的生命周期受光周期强烈影响。在有利季节（以长日为特征），蚜虫种群仅由胎生孤雌生殖的雌性（称为处女蚜）组成。秋天天短被蚜虫感知为预示着严酷季节到来的信号，导致生殖模式发生转变，出现有性形态（产卵雌虫和雄虫），它们交配并产下抗寒（似休眠）的卵。控制两种生殖模式之间转变的分子和细胞基础远未被理解。经典实验在蚜虫大脑的脑间部分（所谓的第一组神经分泌细胞）鉴定出一组神经分泌细胞，它们对胚胎发育为孤雌生殖雌性至关重要，因此被提议合成一种促进孤雌生殖的物质，称为“处女蚜素”。由于胰岛素样肽（ILPs）在其他昆虫的休眠控制中被牵涉，我们研究了它们在蚜虫光周期现象中的参与情况。我们比较了在长日和短日条件下饲养的豌豆蚜 A. pisum 中两种 ILP（ILP1 和 ILP4）和一个胰岛素受体编码基因的表达。这三个基因在长日饲养的蚜虫中表达更高。此外，我们在蚜虫脑中定位了这两个 ILP 基因的表达部位。发现这两个基因都在第一组神经分泌细胞中表达。总的来说，我们的结果表明，ILP1 和 ILP4 在控制蚜虫生命周期中发挥重要作用，通过在长日季节促进孤雌生殖发育，而短日的抑制会激活有性发育。因此，我们提出这些 ILPs 对应早期文献中的所谓“处女蚜素”。还讨论了与生物钟系统的可能联系。
