TcFur1 , a furin 1 ortholog in Tribolium castaneum , regulates reproduction and carbohydrate metabolism without affecting lipid homeostasis

Proprotein convertases of the subtilase family process protein precursors and regulate essential biological processes, including development, metabolism and reproduction. The role of furin 1 (Fur1) in insects remains poorly understood, especially in Tribolium castaneum, a major pest of stored grains. This study describes the TcFur1 ortholog and investigates its effects on development, reproduction and energy metabolism. Phylogenetic analyses establish that TcFur1 is a 1:1 ortholog of type 1 furins from other insects. Quantitative PCR (qPCR) expression profiling indicates that TcFur1 is most highly expressed during the pupal stage, denoting a role in metamorphosis. RNA interference (RNAi)-mediated gene knockdown does not affect viability or development but markedly decreases oviposition in adult females. Triacylglycerol levels and total lipase activity remain unchanged, indicating that TcFur1 is not essential for lipid homeostasis under these conditions. In contrast, TcFur1 knockdown increases circulating trehalose and reduces transcript levels of insulin-like peptides (TcILP1 and TcILP2) and the adipokinetic hormone receptor (TcAKHR), as determined by qPCR. While the corresponding protein levels were not measured due to the lack of specific antibodies, these transcriptional changes are consistent with a role for TcFur1 in the endocrine regulation of carbohydrate metabolism. These results show that TcFur1 is involved in carbohydrate homeostasis and reproduction in T. castaneum, likely through insulin and AKH signalling, without directly affecting lipid metabolism. This data expands the current understanding of proprotein convertase functions in insects and suggests that TcFur1 may serve as a target for RNAi-based population control.