Integrative Proteomics and Metabolomics Analysis of Insect Larva Brain: Novel Insights into the Molecular Mechanism of Insect Wandering Behavior

Before metamorphosis, most holometabolous
insects, such as the
silkworm studied here, undergo a special phase called the wandering
stage. Insects in this stage often display enhanced locomotor activity
(ELA). ELA is vital because it ensures that the insect finds a safe
and suitable place to live through the pupal stage. The physiological
mechanisms of wandering behavior are still unclear. Here, we integrated
proteomics and metabolomics approaches to analyze the brain of the
lepidopteran insect, silkworm, at the feeding and wandering stages.
Using LC–MS/MS and GC–MS, in all we identified 3004
proteins and 37 metabolites at these two stages. Among them, 465 proteins
and 22 metabolites were changed. Neural signal transduction proteins
and metabolites, such as neurofilament, dopaminergic synapse related
proteins, and glutamic acid, were significantly altered, which suggested
that active neural conduction occurred in the brain at the wandering
stage. We also found decreased dopamine degradation at the wandering
stage. The proposed changes in active neural conduction and increased
dopamine concentration might induce ELA. In addition, proteins involved
in the ubiquitin proteasome system and lysosome pathway were upregulated,
revealing that the brain experiences morphological remodeling during
metamorphosis. These findings yielded novel insights into the molecular
mechanism underlying insect wandering behavior.