The role of Tc-foxQ2 in insect neural development analyzed by novel genetic tools (2025)

Abstract

The insect brain serves as a powerful model for deciphering the principles of complex neural architecture. This dissertation investigates the genetic and cellular mechanisms underlying brain development and function in the red flour beetle, Tribolium castaneum, with a specific focus on the highly conserved transcription factor Tc-foxQ2. Our results reveal that Tc-foxQ2 functions as a developmental stage-specific regulator. During embryogenesis, it acts as a fundamental patterning factor essential for gross brain formation and neuronal survival. In contrast, during metamorphosis, its role shifts toward a more refined regulatory function; while its knockdown does not alter the gross brain structure, it causes minor defects in neuronal positioning. By integrating 3D reconstruction with advanced imaging, I characterized the cellular landscape of Tc-foxQ2 in the adult brain, identifying nine distinct neuronal clusters. Remarkably, Tc-foxQ2 marks 71.2% of all dopaminergic neurons. I discovered a unique Tc-foxQ2-positive cluster that connects the mushroom body (MB) and the central complex (CX), providing the first evidence of a transcription factor labeling neurons that bridge these two higher-order centers. Functional analyses through RNAi-mediated knockdown demonstrate that Tc-foxQ2 is essential for the development of these dopaminergic neurons and the regulation of locomotor activity, as its depletion leads to hyperactivity and specific cell loss. Furthermore, to facilitate high-resolution neural imaging, I joined an effort led by another lab to develop and validate a cross-species toolkit of membrane-localizing tags. Tested across ten species from seven phyla, this toolkit provides a robust methodology for labeling cell boundaries. Within Tribolium, the KRas and KRas6R tags were identified as superior tools for precisely localizing fluorescent proteins to the plasma membrane. Collectively, this work identified functional roles for Tc-foxQ2 in regulating motor activity and details of neural circuit formation. These findings provide novel insights into the molecular mechanisms governing insect brain development.

Keywords

Tribolium castaneum; brain development; RNAi; brainbow; 3D reconstruction; behavioral assay; dopaminergic neurons; membrane-localising tags