Neurogenesis in the trunk and brain of the milkweed bug Oncopeltus fasciatus: insights beyond holometabolan models

Current research on insect neurogenesis is focused on Holometabola, which undergo a derived developmental mode that includes metamorphosis, leading to a partial representation of the range of neurogenesis patterns in the embryonic insect nervous system. In this paper, we investigate neurogenesis in the hemimetabolous insect Oncopeltus fasciatus, focusing on both the trunk and brain regions. Our findings reveal early neuroblast formation in the brain, followed by a second phase in the whole embryo. Notably, we did not find gene expression patterns consistent with pro-neural clusters in Oncopeltus, and the brain exhibits characteristics that do not exist in the trunk. We also highlight similarities between segmentation and neurogenesis, proposing that spatial cues play a key role in this differentiation, as both the head and the thorax segment simultaneously. Our analysis suggests that brain development follows a separate trajectory from trunk neurogenesis in at least one neuroblast population that develops earlier than their counterparts. These findings diverge from the commonly presented view of insect neurogenesis and offer new insights into the ancestral roles of key genes involved in neural development.