The Toll Signaling Pathway Targets the Insulin-like Peptide Dilp6 to Inhibit Growth in Drosophila

Abstract

Chronic enteropathogen infection in early childhood reduces circulating insulin-like growth factor 1 (IGF1) levels and restricts growth. Pathogen-derived molecules activate host Toll-like receptors to initiate the immune response, but whether this pathway contributes to growth inhibition is unclear. In Drosophila, activation of Toll receptors in larval fat body suppresses whole-animal growth. Here, using a transcriptomic approach, we identify Drosophila insulin-like peptide 6 (Dilp6), a fat-body-derived IGF1 ortholog, as a selective target of Toll signaling induced by infection or genetic activation of the pathway. Using a tagged allele that we generated to measure endogenous Dilp6, we find a marked reduction in circulating hormone levels. Restoring Dilp6 expression in fat body rescues growth in animals with active Toll signaling. Our results establish that Toll signaling reduces growth by inducing hormone insufficiency, implying a mechanistic link between innate immune signaling and endocrine regulation of growth.

Keywords: Dilp6; Drosophila; Toll; chronic infection; chronic inflammation; enteropathogen; fat body; growth; innate immunity; insulin signaling.