Institut de Biologia Integrativa de Sistemes, Parc Cientific, Universitat de València, C/ Catedràtic Agustín Escardino Benlloch, 9, 46980, Paterna, València, Spain.
Université de Bordeaux, INCIA CNRS UMR, 5287, Talence, France.
Insect Biochem Mol Biol. 2021 Sep;136:103623. doi: 10.1016/j.ibmb.2021.103623. Epub 2021 Jul 9.
Aphids were the first animals described as photoperiodic due to their seasonal switch from viviparous parthenogenesis to sexual reproduction (cyclical parthenogenesis) caused by the shortening of the photoperiod in autumn. This switch produces a single sexual generation of oviparous females and males that mate and lay diapausing cold-resistant eggs that can overcome the unfavourable environmental conditions typical of winter in temperate regions. Previous studies have hinted at a possible implication of two insulin-like peptides (ILP1 and ILP4) in the aphid seasonal response, changing their expression levels between different photoperiodic conditions. Moreover, in situ localization of their transcripts in particular neurosecretory cells (NSCs) in the aphid brain supported the idea that these neuropeptides could correspond to the formerly called virginoparin, an uncharacterized factor originally proposed to be transported directly to the aphid embryos to promote their development as parthenogenetic individuals. To further investigate the fate of these ILPs, we raised a specific antiserum against one of them (ILP4) and mapped this neuropeptide by immunohistochemistry (IHC) in Acyrthosiphon pisum and Megoura viciae aphids. Coincident with in situ localization, our results show that ILP4 is synthesized in two groups (one in each brain hemisphere) of four neurosecretory cells in the pars intercerebralis (NSC group I) and then it is transported outside the brain to the corpora cardiaca. From there, three nerves (two laterals and one medial) transport it to the abdomen. Although no precise site of release has been found, the terminations of these nerves near the germaria would be compatible with the proposal of a direct connection between group I of NSCs and the reproductive system by localized release. In addition, we detected some collateral arborizations originating from the eight NSCs going to the pars lateralis, where clock neurons and some photoreceptors have been previously localized, suggesting a possible communication between the circadian and photoperiodic systems.
蚜虫是第一批被描述为光周期的动物，因为它们在秋季由于光周期缩短，从胎生孤雌生殖转变为有性生殖（周期性孤雌生殖）。这种转变产生了一个单一的有性世代的产卵雌虫和雄虫，它们交配并产下抗寒的休眠卵，这些卵可以克服温带地区冬季典型的不利环境条件。先前的研究表明，两种胰岛素样肽（ILP1 和 ILP4）可能在蚜虫的季节性反应中起作用，它们在不同的光周期条件下改变表达水平。此外，它们的转录本在蚜虫大脑中特定神经分泌细胞（NSC）中的原位定位支持了这样一种观点，即这些神经肽可能对应于以前称为 virginoparin 的物质，这是一种未被表征的因子，最初被提议直接输送到蚜虫胚胎中，以促进它们作为孤雌生殖个体的发育。为了进一步研究这些 ILPs 的命运，我们针对其中一种（ILP4）产生了特异性抗血清，并通过免疫组织化学（IHC）在豌豆蚜和麦长管蚜中对这种神经肽进行了定位。与原位定位一致，我们的结果表明，ILP4 在脑间部的四个神经分泌细胞（NSC 组 I）中的两组（每侧脑半球一组）中合成，然后被运送到脑外的心脏。从那里，三条神经（两条侧神经和一条中神经）将其运送到腹部。虽然尚未找到确切的释放部位，但这些神经在生殖腺附近的末端与 NSCs 组 I 与生殖系统之间通过局部释放建立直接联系的观点是一致的。此外，我们检测到一些起源于 8 个 NSCs 的侧枝，这些 NSCs 分布到侧脑，以前在那里定位了生物钟神经元和一些光感受器，这表明昼夜节律和光周期系统之间可能存在通讯。
