Lactobacillus plantarum gives Drosophila the grow signal

Abstract

Human gut bacteria are implicated in normal metabolism, as well as diseases including diabetes and obesity. Storelli et al report that a single Drosophila gut species, Lactobacillus plantarum, can promote larval growth by modulating TOR and hormonal growth signaling pathways, thereby providing an ideal duo for study of host-microbe interactions.

Figure 1. Overview of data and model for Lactobacillus plantarum (L.p.) stimulation of larval growth

Components shown by Storelli et al to regulate (or correlate with) the growth-promoting effects of L.p. are indicated in blue. Increased larval growth rate and altered InR and E74B gene expression indicate increased systemic signaling by the growth-promoting hormones insulin-like peptides and ecdysone, respectively. Over-expression of the TOR inhibitors TSC1,2 in either fat-body or prothoracic gland (PG) blocked the growth-promoting effect of L.p., indicating a requirement for the TOR nutrient sensing pathway in each of these tissues. The model involves significant inter-tissue signaling: L.p. and dietary protein in the gut lumen signal through the intestinal epithelium to the internal tissues, most likely by increasing circulating titers of amino acids. The Slimfast amino acid transporter transduces this signal to increase TOR signaling in the fat body. The fat-body releases an as-yet-unclear signal (indicated by question mark) that causes specialized brain cells to release insulin-like peptides. The PG receives an unknown signal (perhaps increased circulating amino acid titers?) that stimulates TOR signaling and the secretion of ecdysone. Because L.p. increased larval growth rate without affecting the size of the resultant flies, it suggests that the increased rate of larval growth produced by the fat-body and systemic insulin-like signaling is balanced by an increased rate of transition through developmental stages stimulated by the PG and ecdysone. These results underscore the importance of inter-tissue signaling in coordinating growth and metabolism in response to diet and microbiota.