Progress in the characterization of insulin-like peptides in aphids: Immunohistochemical mapping of ILP4
Insect Biochemistry and Molecular Biology. 2021-09-01; 136: 103623
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Cuti P(1), Barberà M(1), Veenstra JA(2), Martínez-Torres D(3).
(1)Institut de Biologia Integrativa de Sistemes, Parc Cientific, Universitat de València, C/ Catedràtic Agustín Escardino Benlloch, 9, 46980, Paterna, València, Spain.
(2)Université de Bordeaux, INCIA CNRS UMR, 5287, Talence, France.
(3)Institut de Biologia Integrativa de Sistemes, Parc Cientific, Universitat de València, C/ Catedràtic Agustín Escardino Benlloch, 9, 46980, Paterna, València, Spain. Electronic address: .
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.
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